toyota electrical and engine control systems manual

GeneralElectricity is a form of energy called electrical energy. It is sometimes called an "unseen" force because the energy itself cannot be seen, heard, touched, or smelled.

However, the effects of electricity can be seen ... a lamp gives off light; a motor turns; a cigarette lighter gets red hot; a buzzer makes noise.

The effects of electricity can also be heard, felt, and smelled. A loud crack of lightning is easily heard, while a fuse "blowing" may sound like a soft "pop" or "snap." With electricity flowing through them, some insulated wires may feel "warm" and bare wires may produce a "tingling" or, worse, quite a "shock." And, of course, the odor of burned wire insulation is easily smelled.

ELECTRICAL FUNDAMENTALS

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Electron TheoryElectron theory helps to explain electricity. The basic building block for matter, anything that has mass and occupies space, is the atom. All matter - solid, liquid, or gas - is made up of molecules, or atoms joined together. These atoms are the smallest particles into which an element or substance can be divided without losing its properties. There are only about 100 different atoms that make up everything in our world. The features that make one atom different from another also determine its electrical properties.

ATOMIC STRUCTUREAn atom is like a tiny solar system. The center is called the nucleus, made up of tiny particles called protons and neutrons. The nucleus is surrounded by clouds of other tiny particles called electrons. The electrons rotate about the nucleus in fixed paths called shells or rings.

Hydrogen has the simplest atom with one proton in the nucleus and one electron rotating around it. Copper is more complex with 29 electrons in four different rings rotating around a nucleus that has 29 protons and 29 neutrons. Other elements have different atomic structures.



ATOMS AND ELECTRICAL CHARGES

Each atomic particle has an electrical charge. Electrons have a negative (-) charge. Protons have a positive charge. Neutrons have no charge; they are neutral.

In a balanced atom, the number of electrons equals the number of protons. The balance of the opposing negative and positive charges holds the atom together. Like charges repel, unlike charges attract. The positive protons hold the electrons in orbit. Centrifugal force prevents the electrons from moving inward. And, the neutrons cancel the repelling force between protons to hold the atom's core together.

POSITIVE AND NEGATIVE IONS

If an atom gains electrons, it becomes a negative ion. If an atom loses electrons, it becomes a positive ion. Positive ions attract electrons from neighboring atoms to become balanced. This causes electron flow.

ELECTRON FLOW

The number of electrons in the outer orbit (valence shell or ring) determines the atom's ability to conduct electricity. Electrons in the inner rings are closer to the core, strongly attracted to the protons, and are called bound electrons. Electrons in the outer ring are further away from the core, less strongly attracted to the protons, and are called free electrons.

Electrons can be freed by forces such as friction, heat, light, pressure, chemical action, or magnetic action. These freed electrons move away from the electromotive force, or EMF ("electron moving force"), from one atom to the next. A stream of free electrons forms an electrical current.



CONDUCTORS, INSULATORS, SEMICONDUCTORS

The electrical properties of various materials are determined by the number of electrons in the outer ring of their atoms.

• CONDUCTORS - Materials with 1 to 3 electrons in the atom's outer ring make good conductors. The electrons are held loosely, there's room for more, and a low EMF will cause a flow of free electrons.

• INSULATORS - Materials with 5 to 8 electrons in the atom's outer ring are insulators. The electrons are held tightly, the ring's fairly full, and a very high EMF is needed to cause any electron flow at all. Such materials include glass, rubber, and certain plastics.

• SEMICONDUCTORS - Materials with exactly 4 electrons in the atom's outer ring are called semiconductors. They are neither good conductors, nor good insulators. Such materials include carbon, germanium, and silicon.

CURRENT FLOW THEORIES

Two theories describe current flow. The conventional theory, commonly used for automotive systems, says current flows from (+) to (-) ... excess electrons flow from an area of high potential to one of low potential (-). The electron theory, commonly used for electronics, says current flows from (-) to (+) ... excess electrons cause an area of negative potential (-) and flow toward an area lacking electrons, an area of positive potential (+), to balance the charges.

While the direction of current flow makes a difference in the operation of some devices, such as diodes, the direction makes no difference to the three measurable units of electricity: voltage, current, and resistance.



Terms Of Electricity

Electricity cannot be weighed on a scale or measured into a container. But, certain electrical "actions" can be measured.

These actions or "terms" are used to describe electricity; voltage, current, resistance, and power.

VOLTAGE

Voltage is electrical pressure, a potential force or difference in electrical charge between two points. It can push electrical current through a wire, but not through its insulation.

Voltage is pressure

Current is flow.

Resistance opposes flow.

Power is the amount of work performed. It depends on the amount of pressure and the volume of flow.

Voltage is measured in volts. One volt can push a certain amount of current, two volts twice as much, and so on. A voltmeter measures the difference in electrical pressure between two points in volts. A voltmeter is used in parallel.



CURRENT

Current is electrical flow moving through a wire. Current flows in a wire pushed by voltage.

Current is measured in amperes, or amps, for short. An ammeter measures current flow in amps. It is inserted into the path of current flow, or in series, in a circuit.



RESISTANCE

Resistance opposes current flow. It is like electrical "friction." This resistance slows the flow of current. Every electrical component or circuit has resistance. And, this resistance changes electrical energy into another form of energy - heat, light, motion.

Resistance is measured in ohms. A special meter, called an ohmmeter, can measure the resistance of a device in ohms when no current is flowing.



Factors Affecting ResistanceFive factors determine the resistance of conductors. These factors are length of the conductor, diameter, temperature, physical condition and conductor material. The filament of a lamp, the windings of a motor or coil, and the bimetal elements in sensors are conductors. So, these factors apply to circuit wiring as well as working devices or loads.

LENGTHElectrons in motion are constantly colliding as voltage pushes them through a conductor. If two wires are the same material and diameter, the longer wire will have more resistance than the shorter wire. Wire resistance is often listed in ohms per foot (e.g., spark plug cables at 5Ω per foot). Length must be considered when replacing wires.

DIAMETERLarge conductors allow more current flow with less voltage. If two wires are the same material and length, the thinner wire will have more resistance than the thicker wire. Wire resistance tables list ohms per foot for wires of various thicknesses (e.g., size or gauge ... 1, 2, 3 are thicker with less resistance and more current capacity; 18, 20, 22 are thinner with more resistance and less current capacity). Replacement wires and splices must be the proper size for the circuit current.

TEMPERATURE In most conductors, resistance increases as the wire temperature increases. Electrons move faster, but not necessarily in the right direction. Most insulators have less resistance at higher temperatures. Semiconductor devices called thermistors have negative temperature coefficients (NTC) resistance decreases as temperature increases. Toyota's EFI coolant temperature sensor has an NTC thermistor. Other devices use PTC thermistors.

PHYSICAL CONDITIONPartially cut or nicked wire will act like smaller wire with high resistance in the damaged area. A kink in the wire, poor splices, and loose or corroded connections also increase resistance. Take care not to damage wires during testing or stripping insulation.

MATERIALMaterials with many free electrons are good conductors with low resistance to current flow. Materials with many bound electrons are poor conductors (insulators) with high resistance to current flow. Copper, aluminum, gold, and silver have low resistance; rubber, glass, paper, ceramics, plastics, and air have high resistance.



Voltage, Current, AndResistance In Circuits

A simple relationship exists between voltage, current, and resistance in electrical circuits. Understanding this relationship is important for fast, accurate electrical problem diagnosis and repair.

OHM'S LAW

Ohm's Law says: The current in a circuit is directly proportional to the applied voltage and inversely proportional to the amount of resistance.

This means that if the voltage goes up, the current flow will go up, and vice versa. Also, as the resistance goes up, the current goes down, and vice versa.

Ohm's Law can be put to good use in electrical troubleshooting. But, calculating precise values for

voltage, current, and resistance is not always practical ... nor, really needed. A more practical, less time-consuming use of Ohm's Law would be to simply apply the concepts involved:

SOURCE VOLTAGE is not affected by either current or resistance. It is either too low, normal, or too high. If it is too low, current will be low. If it is normal, current will be high if resistance is low or current will be low if resistance is high. If voltage is too high, current will be high.

CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low.

RESISTANCE is not affected by either voltage or current. It is either too low, okay, or too high. If resistance is too low, current will be high at any voltage. If resistance is too high, current will be low if voltage is okay.



ELECTRIC POWER AND WORK

Voltage and current are not measurements of electric power and work. Power, in watts, is a measure of electrical energy ... power (P) equals current in amps (1) times voltage in volts (E), P = I x E. Work, in wattseconds or watt-hours, is a measure of the energy used in a period of time ... work equals power in wafts (W) times time in seconds (s) or hours (h), W = P x time. Electrical energy performs work when it is changed into thermal (heat) energy, radiant (light) energy, audio (sound) energy, mechanical (motive) energy, and chemical energy. It can be measured with a waft-hour meter.



Actions Of Current

Current flow has the following effects; motion, light or heat generation, chemical reaction, and electromagnetism.

HEAT GENERATIONWhen current flows through a lamp filament, defroster grid, or cigarette lighter, heat is generated by changing electrical energy to thermal energy. Fuses melt from the heat generated when too much current flows.

CHEMICAL REACTIONIn a simple battery, a chemical reaction between two different metals and a mixture of acid and water causes a potential energy, or voltage. When the battery is connected to an external load, current will flow. The current will continue flowing until the two metals become similar and the mixture becomes mostly water.

When current is sent into the battery by an alternator or a battery charger, however, the

reaction is reversed. This is a chemical reaction caused by current flow. The current causes an electrochemical reaction that restores the metals and the acid-water mixture.

ELECTROMAGNETISMElectricity and magnetism are closely related. Magnetism can be used to produce electricity. And, electricity can be used to produce magnetism.

All conductors carrying current create a magnetic field. The magnetic field strength is changed by changing current ... stronger (more current), weaker (less current).

With a straight conductor, the magnetic field surrounds it as a series of circular lines of force. With a looped (coil) conductor, the lines of force can be concentrated to make a very strong field. The field strength can be increased by increasing the current, the number of coil turns, or both. A strong electromagnet can be made by placing an iron core inside a coil. Electromagnetism is used in many ways.



Types Of Electricity

There are two types of electricity: static and dynamic. Dynamic electricity can be either direct current (DC) or alternating current (AC).

STATIC ELECTRICITYWhen two non conductors - such as a silk cloth and glass rod - are rubbed together, some electrons are freed. Both materials become electrically charged. One is lacking electrons and is positively charged. The other has extra electrons and is negatively charged. These charges remain on the surface of the material and do not move unless the two materials touch or are connected by a conductor. Since there is no electron flow, this is called static electricity.

DYNAMIC ELECTRICITYWhen electrons are freed from their atoms and flow in a material, this is called dynamic electricity. If the free electrons flow in one direction, the electricity is called direct current (DC). This is the type of current produced by the vehicle's battery. If the free electrons change direction from positive to negative and back repeatedly with time, the electricity is called alternating current (AC). This is the type of current produced by the vehicle's alternator. It is changed to DC for powering the vehicle's electrical system and for charging the battery.




ASSIGNMENT NAME:

1. Describe the atomic structure of an atom and name all it’s components.

2. Explain how an ION differs from an atom.

3. Explain the difference between “bound” and “free” electrons.

4 Explain the function of the “Valence ring”

5. Define the following items: Conductors, Insulators, and Semiconductors.

6. Describe the two theories of electron flow.

7. Define in detail “voltage” and how is it measured.

8. Define in detail “current” and how is it measured.

9. Define in detail “resistance” and how is it measured.

10. Explain the relationship between current and resistance.

11. List and describe the various factors that effect resistance.

12. Explain what ohms law is and how it can be used.

13. Describe the effects of “current flow” through a conductor.

14. Describe in detail the two general categories of “electricity”.

15. Describe the two types of “dynamic electricity”.

Electrical Circuits

A complete path, or circuit, is needed before voltage can cause a current flow through resistances to perform work.

There are several types of circuits, but all require the same basic components. A power source (battery or alternator) produces voltage, or electrical potential. Conductors (wires, printed circuit boards) provide a path for current flow. Working devices, or loads (lamps, motors), change the electrical energy into another form of energy to perform work. Control devices (switches, relays) turn the current flow on and off. And, protection devices (fuses, circuit breakers) interrupt the

current path if too much current flows. Too much current is called an overload, which could damage conductors and working devices.A list of five things to look for in any circuit:

1. Source of Voltage

2. Protection Device

3. Load

4. Control

5. Ground

We will be identifying these items when we look at Automotive Circuits a little later in this book.

ELECTRICAL CIRCUITS

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Types Of Circuits

There are three basic types of circuits: series, parallel, and series-parallel. The type of circuit is determined by how the power source, conductors, loads, and control or protective devices are connected.

SERIES CIRCUIT

A series circuit is the simplest circuit. The conductors, control and protection devices, loads, and power source are connected with only one path for current. The resistance of each device can be different. The same amount of current will flow through each. The voltage across each will be different. If the path is broken, no current flows.

PARALLEL CIRCUIT

A parallel circuit has more than one path for current flow. The same voltage is applied across each branch. If the load resistance in each branch is the same, the current in each branch will be the same. If the load resistance in each branch is different, the current in each branch will be different. If one branch is broken, current will continue flowing to the other branches.

SERIES-PARALLEL CIRCUIT

A series-parallel circuit has some components in series and others in parallel. The power source and control or protection devices are usually in series; the loads are usually in parallel. The same current flows in the series portion, different currents in the parallel portion. The same voltage is applied to parallel devices, different voltages to series devices. If the series portion is broken, current stops flowing in the entire circuit. If a parallel branch is broken, current continues flowing in the series portion and the remaining branches.

ELECTRICAL CIRCUITS


SERIES CIRCUITS

In a series circuit, current has only one path. All the circuit components are connected so that the same amount of current flows through each. The circuit must have continuity. If a wire is disconnected or broken, current stops flowing. If one load is open, none of the loads will work.

Use of Ohm's Law

Applying Ohm's Law to series circuits is easy. Simply add up the load resistances and divide the total resistance into the available voltage to find the current. The voltage drops across the load resistances are then found by multiplying the current by each load resistance. For calculation examples, see page 6 in the Ohms law section.Voltage drop is the difference in voltage (pressure) on one side of a load compared to the

voltage on the other side of the load. The drop or loss in voltage is proportional to the amount of resistance. The higher the resistance, the higher the voltage drop.

When troubleshooting, then, you can see that more resistance will reduce current and less resistance will increase current. Low voltage would also reduce current and high voltage would increase current. Reduced current will affect component operation (dim lamps, slow motors). But, increased current will also affect component operation (early failure, blown fuses). And, of course, no current at all would mean that the entire circuit would not operate. There are electrical faults that can cause such problems and knowing the relationship between voltage, current, and resistance will help to identify the cause of the problem.

ELECTRICAL CIRCUITS


PARALLEL CIRCUITS

In a parallel circuit, current can flow through more than one path from and to the power source. The circuit loads are connected in parallel legs, or branches, across a power source. The points where the current paths split and rejoin are called junctions. The separate current paths are called branch circuits or shunt circuits. Each branch operates independent of the others. If one load opens, the others continue operating.

Use of Ohm's Law

Applying Ohm's Law to parallel circuits is a bit more difficult than with series circuits. The reason is that the branch resistances must be combined to find an equivalent resistance. Just remember that the total resistance in a parallel circuit is less than

the smallest load resistance. This makes sense because current can flow through more than one path. Also, remember that the voltage drop across each branch will be the same because the source voltage is applied to each branch. For examples of how to calculate parallel resistance, see page 6.

When troubleshooting a parallel circuit, the loss of one or more legs will reduce current because the number of paths is reduced. The addition of one or more legs will increase current because the number of paths is increased. Current can also be reduced by low source voltage or by resistance in the path before the branches. And, current can be increased by high source voltage or by one or more legs being bypassed. High resistance in one leg would affect component operation only in that leg.

ELECTRICAL CIRCUITS


SERIES-PARALLEL CIRCUITS

In a series-parallel circuit, current flows through the series portion of the circuit and then splits to flow through the parallel branches of the circuit. Some components are wired in series, others in parallel. Most automotive circuits are series-parallel, and the same relationship between voltage, current, and resistance exists.

Use of Ohm's Law

Applying Ohm's Law to series-parallel circuits is a matter of simply combining the rules seen for series circuits and parallel circuits. First, calculate the equivalent resistance of the parallel loads and add it to the resistances of the loads in series.

The total resistance is then divided into the source voltage to find current. Voltage drop across series loads is current times resistance. Current in branches is voltage divided by resistance. For calculation examples, see page 6.

When troubleshooting a series-parallel circuit, problems in the series portion can shut down the entire circuit while a problem in one leg of the parallel portion may or may not affect the entire circuit, depending on the problem. Very high resistance in one leg would reduce total circuit current, but increase current in other legs. Very low resistance in one leg would increase total circuit current and possibly have the effect of bypassing other legs.

ELECTRICAL CIRCUITS


Ohm's Law

Fast, accurate electrical troubleshooting is easy when you know how voltage, current, and resistance are related. Ohm's Law explains the relationship:

• Current (amps) equals voltage (volts) divided by resistance (ohms) ... I = E ÷ R.

• Voltage (volts) equals current (amps) times resistance (ohms) ... E = I X R.

• Resistance (ohms) equals voltage (volts) divided by current (amps) ... R ÷ E = 1.

USING OHM'S LAW

The effects of different voltages and different resistances on current flow can be seen in the

sample circuits. Current found by dividing voltage by resistance. This can be very helpful when diagnosing electrical problems:

• When the resistance stays the same ... current goes up as voltage goes up, and current goes down as voltage goes down. A discharged battery has low voltage which reduces current. Some devices may fail to operate (slow motor speed). An unregulated alternator may produce too much voltage which increases current. Some devices may fail early (burned-out lamps).

• When the voltage stays the same ... current goes up as resistance goes down, and current goes down as resistance goes up. Bypassed devices reduce resistance, causing high current. Loose connections increase resistance, causing low current.

ELECTRICAL CIRCUITS


SAMPLE CALCULATIONS

Here are some basic formulas you will find helpful in solving more complex electrical problems. They provide the knowledge required for confidence and thorough understanding of basic electricity.

The following abbreviations are used in the formulas:

E = VOLTSI = AMPSR = OHMSP = WATTS

• Ohm's Law

Scientifically stated, it says: "The intensity Of the current in amperes in any electrical circuit is equal to the difference in potential in volts across the circuit divided by the resistance in ohms of the circuit." Simply put it means that current is equal to volts divided by ohms, or expressed as a formula, the law becomes:

I = E / R

or it can be written:

E = I X R

This is important because if you know any two of the quantities, the third may be found by applying the equation.

Ohm's law includes these two ideas:

1. In a circuit, if resistance is constant, current varies directly with voltage.

Now what this means is that if you take a component with a fixed resistance, say a light bulb, and double the voltage you double the current flowing through it. Anyone who has hooked a six-volt bulb to a twelve-volt circuit has experienced this. But it wasn't "too many volts" that burned out the bulb, it was too much current. More about that later.

2. In a circuit, if voltage is constant, current varies inversely with resistance.

This second idea states that when resistance goes up, current goes down. That's why corroded connectors cause very dim lights - not enough current.

• Watts

A watt is an electrical measurement of power or work. It directly relates to horsepower. In fact, in the Sl metric standards that most of the world uses, engine power is given in watts or kilowatts.

Electrical power is easily calculated by the formula:

P = E X I

For instance, a halogen high-beam headlight is rated or 5 amps of current. Figuring 12 volts in the system, we could write:

P = E X IP = 12 X 5P = 60 watts

ELECTRICAL CIRCUITS


RESISTANCE

The effect of individual resistors on the total resistance of a circuit depends on whether the circuit is series or parallel.

Series Circuits

In a series circuit, the total resistance is equal to the sum of the individual resistors:

SERIES:

total R = R1 + R2 + R3 +

That is the basis of the concept of voltage drop. For example, if you had a circuit with three loads in series (a bulb, resistor, and corroded ground) you would add the three together to get total resistance. And, of course, the voltage would drop across each load according to its value.

Parallel Circuits

Parallel circuits are a different story. In a parallel circuit, there are three ways to find total resistance. Method A works in all cases. Method B works only if there are two branches, equal or not. Method C works only if the branches are of equal resistance. A. The total resistance is equal to one over the

sum of the reciprocals of the individual resistors. That sounds confusing, but looking at the formula will make it clearer:

PARALLEL:

n example will make it even clearer. Suppose there is a circuit with three resistors in parallel: 4 ohms, 2 ohms, and 1 ohm. The formula would look like this:

That becomes:

Which becomes:

So there is a little more than one-half ohm resistance in the circuit. You can see that the more resistors in parallel, the less the resistance.

In fact, the total resistance is always less than the smallest resistor. This is why a fuse will blow if you add too many circuits to the fuse. There are so many paths for the current to follow that the total resistance of the circuit is very low. That means the current is very high - so high that the fuse can no longer handle the load.

B. For two resistors:

For a 3 ohm and a 5 ohm resistor that would be:

C. For several identical resistors, divide the value of one resistor by the number of resistors, or:

Where R1 is the value of one resistor and n is the number of resistors. So if you had three 4 ohm resistors in parallel it would be:

ELECTRICAL CIRCUITS


ELECTRICAL CIRCUITS


ELECTRICAL CIRCUITS

ASSIGNMENT NAME:

1. Draw and label the parts of a Series Circuit and a Parallel Circuit.

2. Explain the characteristics of “Voltage” and how it differs between a Series Circuit and a Parallel Circuit.

3. Explain the characteristics of “Current” and how it differs between a Series Circuit and a Parallel Circuit.

4. Explain the characteristics of “Resistance” and how it differs between a Series Circuit and a Parallel Circuit.

Power Sources On The Car

Two power sources are used on Toyota vehicles. When the engine is not running or is being started, the battery provides power. When the engine is running, the alternator provides power for the vehicle's loads and for recharging the battery.

THE BATTERY

The battery is the primary "source" of electrical energy on Toyota vehicles when the engine is not running or is being started. It uses an electrochemical reaction to change chemical energy into electrical energy for starting, ignition, charging, lighting, and accessories.

All Toyota vehicles use a 12-volt battery. Batteries have polarity markings ... the larger (thicker)

terminal is marked "plus" or "POS" (+), the other terminal is marked “minus" or "NEG" (-). Correct polarity is important; components can be damaged if the battery is connected backwards.

THE ALTERNATOR

The alternator is the heart of the vehicle's electrical system when the engine is running. It uses electromagnetism to change some of the engine's mechanical energy into electrical energy for powering the vehicle's loads and for charging the battery.

All Toyota alternators are rated by amps of current output ... from 40 to 80 amps.

ELECTRICAL COMPONENTS


Loads

Working devices - or loads - consume electricity. They change electrical energy into another form of energy to do work. This energy may be thermal (heat), radiant (light), mechanical (motive), audio (sound), chemical, or magnetic. The electrical energy is changed by the resistance of the working device. Resistance is put to work in many ways on Toyota vehicles.

PERFORM WORK

Some components use resistance to reduce current flow and change electrical energy (voltage) into heat, light, or motion. Resistance produces heat in electric window defrosters and cigarette lighters. Resistance produces light in lamp filaments. And, resistance produces motion in motors and solenoid coils. All circuit loads use resistance to perform work.

CONTROL CURRENT

Other components and systems use resistance for current control. Ignition primary resistors, also called ballast resistors, maintain and protect the electronic control unit (ECU) from excessive current. The headlamp rheostat adds or subtracts resistance to dim or brighten interior lamps. A carbon pile resistance in the Sun VAT-40 tester "loads" the battery for cranking-voltage and charging system tests. A sliding contact resistance is used on some A/C and heating controls to adjust interior temperature by increasing or decreasing air volume and fan speed. A wire-wound resistor is used on some fuel pumps to reduce pump speed.

REDUCE ARCING AND "RFI"

Some ignition components use resistance to reduce arcing and radio frequency interference (RFI). Condensers use the high resistance of a dielectric (insulating) material to separate conductive plates that soak up electrostatic charges and current surges that cause RFI and point arcing. Spark plug cables, also called carbon resistance wires, reduce current flow but transmit high voltage to the spark plugs. This causes an extremely hot spark without RFI or rapid burning of the plug electrodes. Spark plugs, themselves, have a carbon core to achieve the same results.

SENSE OPERATING CONDITIONS

Other components use resistance in sensing and monitoring operating conditions. The resistance added to or subtracted from a sensing circuit changes the current flow which is used for input to a control device, gauge, or actuator. The coolant temperature sensor uses a device that changes resistance with temperature. The fuel-level sensor uses a type of potentiometer, or sliding-contactresistance. The automatic headlamp control uses aphotoresistor. The manifold vacuum sensor uses a crystal which changes resistance with pressure. And, with the use of electronic control systems growing rapidly, many more sensors and actuators are using the variation of resistance to operate.



Types Of Resistors

Three basic types of resistors are use a m automotive electrical systems ... fixed value, stepped or tapped, and variable. Different symbols are used for the different types of resistors.

FIXED-VALUE RESISTORS

Two types of fixed-value resistors are used: wire-wound and carbon.

Wire-wound resistors are made with coils of resistance wire. Sometimes called power

resistors, they are very accurate and heat stable. The resistance value is marked.

Carbon resistors are common in Toyota electronic systems. Carbon is mixed with binder; the more carbon, the lower the resistance. Some have the resistance value stamped on, others are rated by wafts of power; most have color-code bands to show the resistance value. Four bands are used ... the first two bands give the resistance digits, the next band is the number of zeros, and the last band gives the "tolerance."

A resistor with four bands - red, green, black, and brown from left to right - would be sized as follows:

• The first two bands set the digits ... red (2), green (5).

• The next band is the number of zeros. Black is "0" zeros. So the resistor has a base value of 25Ω.

• And, the last band is the tolerance ... brown (1 %). So, the resistance value is "25 ohms plus or minus .25 ohms" (24.75Ω to 25.25Ω ).



STEPPED OR TAPPED RESISTORSStepped or tapped resistors have two or more fixed resistance values. The different resistances (carbon or wire) are connected to different terminals in a switch. As the switch is moved, different resistance values are placed in the circuit. A typical Toyota application is in the heater motor's blower-fan switch.

VARIABLE RESISTORSThree types of variable resistors are used: rheostats, potentiometers, and thermistors.• RHEOSTAT - Toyota uses a rheostat on the

headlamp switch to dim or brighten dash panel lighting. Rheostats have two connections ... one to the fixed end of a resistor, one to a sliding contact on the resistor. Turning the control moves the sliding contact away from or toward the fixed end, increasing or decreasing the resistance.

• POTENTIOMETER - Toyota uses a potentiometer in the EFI airflow meter. Potentiometers have three connections ... one at each end of a resistor and one on a sliding contact. Turning the control places more or less resistance in the circuit.

• THERMISTOR - Toyota uses NTC (negative temperature coefficient) thermistors in

temperature sensors and PTC (positive temperature coefficient) thermistors in the electric assist choke. Both types of thermistors change resistance with increasing temperature (NTC, resistance goes down as temperature goes up; PTC, resistance goes up as temperature go up.)



Controls

Control devices used in electrical circuits on Toyota vehicles include a variety of switches, relays, and solenoids. Electronic control devices include capacitors, diodes, and transistors. Controls are needed to start, stop, or redirect current flow. Most switches require physical movement for operation, relays and solenoids are operated with electromagnetism, electronic controls are operated electrically.

SWITCHES

Switches are the most common circuit control device. They usually have two or more sets of contacts. Opening the contacts is called "opening" or "breaking the circuit," while closing the contacts is called "closing" or "making" the circuit. "Poles" refer to the number of input circuit terminals. "Throws" refer to the number of output circuits. Such switches are referred to as SPST (single-pole, single-throw), SPDT (single-pole, double-throw), and MPMT (multiple-pole, multiple-throw).

The various types of switches include:

• Hinged pawl - a simple SPST switch to make or break a circuit.

• Momentary contact - another SPST switch, normally open or closed, which makes or breaks the circuit when pressed ... typically used for the

horn switch.

• SPDT - one wire in, two wires out ... commonly used in high-beam / low-beam headlamp circuits.

• MPMT - movable contacts are linked to sets of output terminals ... may be used for the

transmission neutral start switch.

• Mercury switch - liquid mercury flows between contacts to make circuit ... commonly used to turn

engine compartment and trunk lamps on and off.

• Temperature-sensitive switch - a bimetal element bends when heated to make contact completing a circuit or to break contact opening a circuit. The same principle is also used in time-delay switches and flashers.



RELAYSA relay is simply a remote-control switch, which uses a small amount of current to control a large amount of current. A typical relay has a control circuit and a power circuit. The control circuit is fed current by the power source, and the current flows through a switch and an electromagnetic coil to ground. The power circuit is also fed current from the power source, and the current flows to an armature which can be attracted by the magnetic force on the coil.

In operation, when the control circuit switch is open, no current flows to the relay. The coil is not energized, the contacts are open, and no power goes to the load. When the control circuit switch is closed, however, current flows to the relay and energizes the coil. The resulting magnetic field pulls the armature down, closing the contacts and allowing power to the load.

Many relays are used on Toyotas for controlling high current in one circuit with low current in another circuit. The relay control circuit can be switched from the power supply side or, more common in Toyotas, from the ground side.

SOLENOIDSSolenoids are electromagnetic switches with a movable core that converts current flow into mechanical movement.

In a "pulling" type solenoid, the magnetic field pulls a core into a coil. These solenoids are called magnetic switches on Toyota starters. A pull-in coil "pulls" the core into the coil, and a hold-in coil "holds" the core in place.

In a "push-pull" type solenoid, a permanent magnet is used for the core. By changing the direction of current flow, the core is "pulled in" or "pushed out." A typical use is on electric door locks.



CAPACITORS

Capacitors use an electrostatic field to "soak up" or store an electrical charge. In a circuit, a capacitor will build up a charge on its negative plate. Current flows until the capacitor charge is the same as that of the power source. It will hold this charge until it is discharged through another circuit (such as ground). Always handle capacitors with care; once charged, they can be quite shocking long after the power is removed.

• TYPES

A capacitor has two conducting plates separated by an insulating material or dielectric. Three types are used: ceramic for electronic circuits, paper and foil for noise suppression in charging and ignition systems, and electrolytic for turn-signal flashers. Different symbols are used for ordinary and electrolytic capacitors.

• RATINGS

Automotive capacitors are rated in microfarads, and the rating is usually stamped on the case. Always choose a capacitor rated for the maximum expected voltage.

• DIAGNOSIS / TESTING

Capacitors can be tested for short circuits using an ohmmeter. Connect one test lead to the capacitor mounting clip and the other test lead to the capacitor pigtail connector. The meter needle will first show some continuity as the meter's battery charges the capacitor, then will swing to infinite resistance (∞). If only continuity is seen, the capacitor is most likely shorted.



Electronics"Electronic" devices and systems provide today's vehicles with added comfort, convenience, safety, and performance.

These devices and systems, like their "electrical" counterparts, control electricity to do work. The current flows through a semiconductor - rather than through wires. The movement usually produces an electrical signal - rather than heat, light, or motion. And, this signal may be transmitted, amplified, or used in special circuits to perform logical decision-making functions.

Since there are seldom any moving (electromechanical) parts, these devices and systems are often called solid-state electronics.

SEMICONDUCTORSSemiconductors can act like conductors or insulators. They have a resistance higher than that of conductors like copper or iron, but lower than that of insulators like glass or rubber. They have special electrical properties:• Conductivity can be increased by mixing in certain substances;• Resistance can be changed by light, temperature, or mechanical pressure; and,• Light can be produced by passing current through them.

DIODESDiodes are semiconductor devices which act as one way electrical check valves. Diodes will allow current flow in one direction (anode to cathode), but block it in the reverse direction (cathode to anode).

• TYPES / USESThere are several types of diodes. Rectifying diodes change low-current AC to DC in the charging system. Power rectifiers can handle larger currents in electronic power supplies. Zener diodes can function as voltage sensitive switches. They turn "on" to allow current flow once a certain voltage is reached. They are often used in voltage regulation applications. Light-emitting diodes (LEDs) are used for indicator lights and digital displays. And, photodiodes detect light for sensors.

• SYMBOLSSymbols for various diodes are shown. The arrow points in the "forward" direction of current flow (anode to cathode). Zener diodes have a "Z" shaped bar on the cathode side. LEDs and photodiodes are enclosed in a circle with incoming or outgoing light indicated.



TransistorsTransistors are semiconductor devices for controlling current flow. A "transistor" (transformer + resistor) transfers signals across the resistance of two semiconductor materials.

• TYPES / USESThere are many types of transistors. Ordinary or bipolar transistors are most common for switching and amplifying. Power transistors are a variation for larger currents; exposed metal carries away heat. Phototransistors are another variation, used as light-sensitive switches in speedometer and headlamp systems.

Field-effect transistors (FETs) are quite different. They are used as switches, amplifiers, and voltage controlled resistors.

• SYMBOLSBipolar transistors are shown with a line and arrow for the emitter, a heavy T-shaped line for the base, and a line without an arrow for the collector. The emitter arrow points to the circuit's negative side. Phototransistors have incoming light arrows added. And, FETs have an arrow showing negative (N) or positive (P) voltage.

• OPERATIONIn bipolar transistors, a small base current (I b) between the emitter-base "turns on" the transistor and causes a larger current (I c) to flow between the emitter-collector. In phototransistors, light striking the base "turns on" the transistor. This switches on a second transistor which amplifies the signal.

ELECTRONIC CIRCUITS AND SYSTEMSIndividual semiconductor devices are called discrete devices, a number of them may be used in a circuit. Such devices are common in charging, ignition, and headlamp circuits that handle large amounts of power.

The more sophisticated electronic control systems now being used on the vehicle, however, make use of integrated circuits and microprocessors or onboard computers.

• INTEGRATED CIRCUITSAn integrated circuit (IC) has hundreds, even thousands, of discrete devices on a single silicon chip. These include diodes, transistors, resistors, and capacitors. The IC is usually packaged in ceramic or plastic and each tiny device inside is connected to one or more leads that plug into a larger on-vehicle circuit. One type can process analog signals - those that change continuously with time. Another type can process digital signals - those that change intermittently "on" or "off" with time.

• MICROPROCESSORSMicroprocessors, or on-board computers, are used on various electronic control systems. Such systems have three basic parts: 1) sensors tell what is happening; 2) the microprocessor computes the data and decides what to do; and 3) the actuators or controls respond to change or display the condition. The ECS and ABS are examples of such systems.



Protective Devices

Electrical circuits are protected from too much current by fuses, fusible links, and circuit breakers. Such devices will interrupt a circuit to prevent high current from melting conductors and damaging loads. Each of these circuit protection devices is sensitive to current, not voltage, and is rated by current-carrying capacity. They are usually located at, or near, the power source for the circuit being protected. As such, they are usually a good starting point during electrical problem troubleshooting. Remember, though, these devices "blow" or open a circuit because of a problem. Always locate and correct the problem before replacing a fuse or fusible link or resetting a circuit breaker.

FUSES

Fuses are the most common circuit protection device. Fuses have a fusible element, or low-

melting-point metal strip, in a glass tube or plug-in plastic cartridge. These fuses are located in a fuse block under the dash or behind a kick panel. Most circuits - other than the headlamp, starter, and ignition systems - receive power through the fuse block. Battery voltage is supplied to a buss bar in the block. One end of each fuse is connected to this bar, the other end to the circuit it protects.

Fuse ratings range from 0.5 to 35 amps, but 7.5 -amp to 20-amp fuses are most common.



FUSIBLE LINKS

Some circuits use fusible links, or fuse links, for overload protection. Toyotas can have as many as six fusible links protecting circuits for charging, starting, ignition, and certain accessories. Check the "Power Source" page in the Electrical Wiring Diagram manual for the specific vehicle.

A fusible link is a short length of smaller gauge wire installed in a circuit with larger conductors. High current will melt the link before it melts the circuit wiring. Such fuse links have special insulation that blisters or bubbles when the link melts. A melted link must be replaced with one of the same size after the cause of the overload has been identified and the problem corrected.

CIRCUIT BREAKERS

Circuit breakers are used for protecting circuits temporary overloads may occur and where power must be quickly restored. A bimetal strip is used, similar to that in a temperature-sensitive switch. When heated, the two metals expand differently and cause the strip to bend. The "breaker" is normally closed and it opens when the bimetal element bends. Some circuit breakers are self-resetting, others must be manually reset.

Circuit breakers are used on Toyota vehicles to protect circuits for the defogger, heater, air conditioner, power windows, power door locks, and sun roof.




ASSIGNMENT NAME:

1. Describe two power sources used in a vehicle.

2. Explain the term “load” and how it is used in a circuit.

3. Describe the two types of resistors and how each is used.

4. Explain the color code of a resistor that is: “Brown, Orange, Red, Silver.

5. Describe a “stepped resistor “ and how it differs from a “fixed resister”.

6. List and describe three types of “variable resistors”.

7. Explain how a “NTC” thermistor differs from a “PTC” thermistor.

8. List six types of switches used in automobiles.

9. Describe the two circuits used in a relay.

10 Explain how a “relay” differs from a “solenoid”.

11. Explain how current flows into a “capacitor”.

12. Explain the term “semiconductor”.

13. Draw, label, and describe the basic function of a “diode”.

14. Draw, label, and describe the basic function of a “bi-polar transistor”.

15. Explain the term “Integrated Circuit”.

16. List three types of “circuit protective devices”.

17. Describe the basic construction of a “fuse” or “fuse element”.

18. Explain how a “fuse element” differs from a “fusible link”.

19. Describe the basic construction of a “circuit breaker”.

ANALOG VS. DIGITAL METERS

Ultimately, your diagnosis of vehicleelectrical system problems will comedown to using a voltmeter, ammeter, orohmmeter to pinpoint the exact location ofthe problem. There are two types of eachmeter—analog and digital.

Analog meters use a needle andcalibrated scale to indicate values.

Digital meters display those values on adigital display.

This chapter will help you understandhow these meters work as well as theadvantages and disadvantages of each.

Before using a meter, read themanufacturer's operating instructions.Reading analog meters usually requiressimple mental calculations. For example,a meter might have three voltage ranges:4.0 V, 20 V and 40 V, but only two scales:4.0 V and 20 V. In order to use the 40 Vrange, you need to multiply the needlereading on the 4.0 V scale by 10 (or forthat matter, the 20 V scale by 2).

Digital meters are usually simpler toread and many will adjust to the properrange required for the circuit or devicethey are

connected to. These meters are known asauto-ranging meters. Other digitalmeters require the operator to select theproper range. In any case it is importantto learn the symbols used in a digitalreadout so you can interpret the reading.The electrical units of measure symbolsare:

M for mega or million K for kilo or thousand m for milli or one-thousandth u for micro or one-millionth

The three types of meters—voltmeters,ammeters and ohmmeters—connect tothe circuits or devices in different ways.This is necessary to get accuratemeasurements and to prevent damage tothe meters.

VOLTMETERS— ANALOG AND DIGITAL

Voltmeters measure voltage or voltagedrop in a circuit. Voltage drop can beused to locate excessive resistance in thecircuit which could cause poorperformance or improper operation. Lackof voltage at a given point may indicate anopen circuit or ground. On the otherhand, low voltage or high voltage drop,may indicate a high resistance problemlike a poor connection.

Voltmeters must be connected in parallelwith the device or circuit so that themeter can tap off a small amount ofcurrent. That is, the positive or red lead isconnected to the circuit closest to thepositive side of the battery. The negativeor black lead is connected to ground or thenegative side of the circuit. If a voltmeteris connected in series, its high resistancewould reduce circuit current and cause afalse reading.

ANALOG AND DIGITAL METERS


Because voltmeters are always hooked toa circuit in parallel, they become part ofthe circuit and reduce the total resistanceof the circuit. If a voltmeter has aresistance that is too low in comparison tothe circuit, it will give a falsemeasurement. The false reading is due tothe meter changing the circuit bylowering the resistance, which increases

the current flow in the circuit. The effecta voltmeter has on the circuit to which itis attached is sometimes referred to as"loading effect" of the meter. The loadingeffect a voltmeter has on a circuit isdetermined by the total resistance of thecircuit in relation to the impedance of thevoltmeter.

Every voltmeter has an impedance,which is the meter's internal resistance.The impedance of a conventional analogvoltmeter is expressed in "ohms per volt."The amount of resistance an analogvoltmeter represents to the circuitchanges in relation to the scale on whichit is placed. Digital voltmeters, on theother hand, have a fixed impedancewhich does not change from scale to scaleand is usually 10 M ohms or more.

Impedance is the biggest differencebetween analog and digital voltmeters.Since most digital voltmeters have 50times more impedance than analogvoltmeters, digital meters are moreaccurate when measuring voltage inhigh resistance circuits.

For example, if you are using a lowimpedance (20,000 ohms per volt) analogmeter on the 20 volt scale (the voltmeterrepresents 400,000 ohms resistance to thecircuit) to measure voltage drop across a1,000,000 ohm component in a circuit, twoand a half times as much current isflowing through the meter than throughthe component. You are no longermeasuring just that component, but thecomponent plus your meter, giving you afalse reading of the actual voltage dropacross the component. This situationmight lead you to believe the voltage at thecomponent is low or that there is highresistance somewhere in the circuit orthat the component is defective when it isjust the meter you are using.

If you use a digital meter with 10 millionohms of impedance to test the samecomponent, only 1/10 of the current willflow through the meter, which means ithas very little effect on the circuit beingmeasured.



AMMETERS— ANALOG AND DIGITAL

Ammeters measure amperage, orcurrent flow, in a circuit, and provideinformation on current draw as well ascircuit continuity. High current flowindicates a short circuit, unintentionalground or a defective component. Sometype of defect has lowered the circuitresistance. Low current flow mayindicate high resistance or a poorconnection in the circuit or a dischargedbattery. No current indicates an opencircuit or loss of power.

Ammeters must always be connected inseries with the circuit, never in parallel.That is, all the circuit current must flowthrough the meter. It is connected byattaching the positive lead to the positiveor battery side of the circuit, and thenegative lead to negative or ground side ofthe circuit, as shown. CAUTION: These meters have extremely lowinternal resistance. If connected in parallel, thecurrent running through the parallel branchcreated by the meter might be high enough todamage the meter along with the circuit the meteris connected to. Also, since all the current willflow through the ammeter when it is connected besure that the circuit current will not exceed themaximum rating of the meter.

There is not a great difference betweenanalog and digital ammeters. Digitalmeters are often capable of measuringsmaller currents, all the way down tomicroamps. They are easier to usebecause they give a specific value,eliminating the need to interpret theanalog meter's needle on its scale.Generally speaking, most digitalammeters are combined with a voltmeter.

OHMMETERS— ANALOG AND DIGITAL

An ohmmeter is powered by an internalbattery that applies a small voltage to acircuit or component and measures howmuch current flows through the circuitor component. It then displays the resultas resistance. Ohmmeters are used for

checking continuity and for measuringthe resistance of components. Zeroresistance indicates a short while infiniteresistance indicates an open in a circuitor device. A reading higher than thespecification indicates a faulty componentor a high resistance problem such asburnt contacts, corroded terminals orloose connections.



Ohmmeters, because they are self-powered, must never be connected to apowered circuit as this may blow a fuse inthe meter and damage its battery. Unlessthe circuit being measured contains adiode, polarity (attaching the leads in aparticular order) is inconsequential.

An analog ohmmeter should becalibrated regularly by connecting the twoleads together and zeroing the meter withthe adjust knob. This compensates forchanges in the state of charge of theinternal battery.

CAUTION: Analog ohmmeters may apply ahigher voltage to a circuit than a digitalohmmeter, causing damage to solid statecomponents. Use analog ohmmeters with care. Digital meters,on the other hand, apply less voltage to a circuit, sodamage is less likely.

Analog meters can also bias, or turn on,semi-conductors and change the circuitby allowing current to flow to otherportions of the circuit.

Most digital meters have a low voltagesetting which will not bias semi-conductors and a higher voltage settingfor testing semiconductors. Theinformation displayed on a digital meterin the diode test function differs from onemeter brand to another. Some digitalmeters will display a value whichrepresents the perceived resistance of the diode in forward bias. Other meterswill display the forward bias voltage dropof the diode.

Digital ohmmeters do have onelimitation. Due to the small amount ofcurrent they pass through the devicebeing tested, they cannot check somesemiconductors in circuits, such as aclamping diode on a relay coil.

Many analog ohmmeters will, whenswitched to the ohm function, reverse thepolarity of the test leads. In other words,the red lead may become negative and theblack lead may become positive. Themeter will function properly as long asyou are aware of this and reverse theleads. This is especially important whenworking with diodes or transistors whichare polarity sensitive and only allowcurrent to flow from the positive to thenegative end. To check for polarityreversal, set the ohmmeter in ohmfunction and connect its leads to the leadsof a voltmeter (red to red, black to black).If the voltmeter shows a negative value,that particular ohmmeter reversespolarity in ohm function. Most digitalmeters do not reverse polarity.

You should note that ohmmeters do littlegood in low resistance, high current-carrying circuits such as starters. Theycannot find points of high resistancebecause they only use a small amount ofcurrent from their internal batteries. In alarge conductor (such as a battery cable),this current meets little resistance. Avoltage drop test during circuit operationis much more effective at locating pointsof high resistance in this type of circuit.

Taken with permission from the Toyota Advanced Electrical Course#672,




ASSIGNMENT NAME:

1. Explain how reading an Analog meter differs from a Digital meter.

2. Explain the following electrical units of measure symbols ( M, K, m, u ).

3. List three types of meters.

4. Describe how voltmeters are connected to a circuit.

5. Explain how “meter loading” affects the circuit.

6. Describe “meter impedance” and how it effects a circuit?

7. List the fixed impedance value of a digital voltmeter.

8. Explain how the impedance of a digital meter differs from an analog meter.

9. Describe how ammeters are connected to a circuit.

10. Explain how analog ohmmeters differ from digital ohmmeters in setup.

11. Explain what precautions one should take while connecting an ohmmeter to a circuit.

CONDUCTORS

Conductors are needed to complete the path for electrical current to flow from the power source to the working devices and back to the power source.

POWER OR INSULATED CONDUCTORS

Conductors for the power or insulated current path may be solid wire, stranded wire, or printed circuit boards. Solid, thin wire can be used when current is low. Stranded, thick wire is used when current is high. Printed circuitry - copper conductors printed on an insulating material with connectors in place - is used where space is limited, such as behind instrument panels.

Special wiring is needed for battery cables and for ignition cables. Battery cables are usually very thick, stranded wires with thick insulation. Ignition cables usually have a conductive carbon core to reduce radio interference.

GROUND PATHS

Wiring is only half the circuit in Toyota electrical systems. This is called the "power" or insulated side of the circuit. The other half of the path for current flow is the vehicle's engine, frame, and body. This is called the ground side of the circuit. These systems are called single-wire or ground-return systems.

A thick, insulated cable connects the battery's positive ( + ) terminal to the vehicle loads. As insulated cable connects the battery's negative ( - ) cable to the engine or frame. An additional grounding cable may be connected between the engine and body or frame.

Resistance in the insulated side of each circuit will vary depending on the length of wiring and the number and types of loads. Resistance on the ground side of all circuits must be virtually zero. This is especially important: Ground connections must be secure to complete the circuit. Loose or corroded ground connections will add too much resistance for proper circuit operation.

SYSTEM POLARITY

System polarity refers to the connections of the positive and negative terminals of the battery to the insulated and ground sides of the electrical system. On Toyota vehicles, the positive (+) battery terminal is connected to the insulated side of the system. This is called a negative ground system having positive polarity.

Knowing the polarity is extremely important for proper service. Reversed polarity may damage alternator diodes, cause improper operation of the ignition coil and spark plugs, and may damage other devices such as electronic control units, test meters, and instrument panel gauges.

WIRE, TERMINAL AND CONNECTOR REPAIR


HARNESSES

Harnesses are bundles of wires that are grouped together in plastic tubing, wrapped with tape, or molded into a flat strip. The colored insulation of various wires allows circuit tracing. While the harnesses organize and protect wires going to common circuits, don't over look the possibility of a problem inside.

WIRE INSULATION

Conductors must be insulated with a covering or "jacket." This insulation prevents physical damage, and, more important, keeps the current flow in the wire. Various types of insulation are used depending on the type of conductor. Rubber, plastic, paper, ceramics, and glass are good insulators.

CONNECTORS

Various types of connectors, terminals, and junction blocks are used on Toyota vehicles. The wiring diagrams identify each type used in a circuit. Connectors make excellent test points because the circuit can be "opened" without need for wire repairs after testing. However, never assume a connection is good simply because the terminals seem connected. Many electrical problems can be traced to loose, corroded, or improper connections. These problems include a missing or bent connector pin.



CONNECTOR REPAIR

The repair parts now in supply are limited to those connectors having common shapes and terminal cavity numbers. Therefore, when there is no available replacement connector of the same shape or terminal cavity number, please use one of the alternative methods described below. Make sure that the terminals are placed in the original order in the connector cavities, if possible, to aid in future diagnosis.

1 . When a connector with a different number of terminals than the original part is used, select a connector having more terminal cavities than required, and replace both the male and female connector parts.

Example: You need a connector with six terminals, but the only replacement available is a connector with eight terminal cavities. Replace both the male and female connector parts with the eight terminal part, transfering the terminals from the old connectors to the new connector.

2. When several different type terminals are used in one connector, select an appropriate male and female connector part for each terminal type used, and replace both male and female connector parts.

Example: You need to replace a connector that has two different types of terminals in one connector. Replace the original connector with two new connectors, one connector for one type of terminal, another connector for the other type of terminal.

3. When a different shape of connector is used, first select from available parts a connector with the appropriate number of terminal cavities, and one that uses terminals of the same size as, or larger than, the terminal size in the vehicle. The wire lead on the replacement terminal must also be the same size as, or larger than, the nominal size of the wire in the vehicle. ("Nominal" size may be found by looking at the illustrations in the back of this book or by direct measurement across the diameter of the insulation). Replace all existing terminals with the new terminals, then insert the terminals into the new connector.

Example: You need to replace a connector that is round and has six terminal cavities. The only round replacement connector has three terminal cavities. You would select a replacement connector that has six or more terminal cavities and is not round, then select terminals that will fit the new connector. Replace the existing terminals, then insert them into the new connector and join the connector together.



CONDUCTOR REPAIR

Conductor repairs are sometimes needed because of wire damage caused by electrical faults or by physical abuse. Wires may be damaged electrically by short circuits between wires or from wires to ground. Fusible links may melt from current overloads. Wires may be damaged physically by scraped or cut insulation, chemical or heat exposure, or breaks caused during testing or component repairs.

WIRE SIZE

Choosing the proper size of wire when making circuit repairs is critical. While choosing wires too thick for the circuit will only make splicing a bit more difficult, choosing wires too thin may limit current flow to unacceptable levels or even result in melted wires. Two size factors must be considered: wire gauge number and wire length.

• WIRE GAUGE NUMBERWire gauge numbers are determined by the conductor's cross-section area.

In the American Wire Gauge system, "gauge" numbers are assigned to wires of different thicknesses. While the gauge numbers are not directly comparable to wire diameters and cross-section areas, higher numbers (16, 18, 20) are assigned to increasingly thinner wires and lower numbers (1, 0, 2/0) are assigned to increasingly thicker wires. The chart shows AWG gauge numbers for various thicknesses.

Wire cross-section area in the AWG system is measured in circular mils. A mil is a thousandth of an inch (0.001). A circular mil is the area of a circle 1 mil (0.001) in diameter.

In the metric system used worldwide, wire sizes are based on the cross-section area in square millimeters (mm 2 ). These are not the same as AWG sizes in circular mils. The chart shows AWG size equivalents for various metric sizes.

• WIRE LENGTHWire length must be considered when repairing circuits because resistance increases with longer lengths. For instance, a 16-gauge wire can carry an 18-amp load for 10 feet without excessive voltage drop. But, if the section of wiring being replaced is only 3-feet long, an 18-gauge wire can be used. Never use a heavier wire than necessary, but - more important - never use a wire that will be too small for the load.



WIRE REPAIRS

• Cut insulation should be wrapped with tape or covered with heat-shrink tubing. In both cases, overlap the repair about 1/2-inch on either side.

• If damaged wire needs replacement, make sure the same or larger size is used. Also, attempt to use the same color. Wire strippers will remove insulation without breaking or nicking the wire strands.

• When splicing wires, make sure the battery is disconnected. Clean the wire ends. Crimp and solder them using rosin-core, not acid-core, solder.

• SOLDERING

Soldering joins two pieces of metal together with a lead and tin alloy.

In soldering, the wires should be spliced together with a crimp. The less solder separating the wire strands, the stronger the joint.

• SOLDER

Solder is a mixture of lead and tin plus traces of other substances.

Flux core wire solder (wire solderwith a hollow center filled with flux) is recommended for electrical splices.

• SOLDERING FLUX

Soldering heats the wires. In so doing, it accelerates oxidization, leaving a thin film of oxide on the wires that tends to reject solder. Flux removes this oxide and prevents further oxidation during the soldering process.

Rosin or resin-type flux must be used for all electrical work. The residue will not cause corrosion, nor will it conduct electricity.

• SOLDERING IRONS

The soldering iron should be the right size for the job. An iron that is too small will require excessive time to heat the work and may never heat it properly. A low-wattage (25-100 W) iron works best for wiring repairs.

• CLEANING WORK

All traces of paint, rust, grease, and scale must be removed. Good soldering requires clean, tight splices.



• TINNING THE IRON

The soldering iron tip is made of copper. Through the solvent action of solder and prolonged heating, it will pit and corrode. An oxidized or corroded tip will not satisfactorily transfer heat from the iron to the work. It should be cleaned and tinned. Use a file and dress the tip down to the bare copper. File the surfaces smooth and flat.

Then, plug the iron in. When the tip color begins to change to brown and light purple, dip the tip in and out of a can of soldering flux (rosin type). Quickly apply rosin core wire solder to all surfaces.

The iron must be at operating temperature to tin properly. When the iron is at the proper temperature, solder will melt quickly and flow freely. Never try to solder until the iron is properly tinned.

• SOLDERING WIRE SPLICES

Apply the tip flat against the splice. Apply rosin-core wire solder to the flat of the iron where it contacts the splice. As the wire heats, the solder will flow through the splice.

• RULES FOR GOOD SOLDERING

1. Clean wires.

2. Wires should be crimped together.

3. Iron must be the right size and must be hot.

4. Iron tip must be tinned.

5. Apply full surface of soldering tip to the splice.

6. Heat wires until solder flows readily.

7. Use rosin-core solder.

8. Apply enough solder to form a secure splice.

9. Do not move splice until solder sets.

10. Place hot iron in a stand or on a protective pad.

11. Unplug iron as soon as you are finished.



Step 1. Identify the connector and terminal type.

1. Replacing Terminals

a. Identify the connector name, position of the locking clips, the un-locking direction and terminal type from the pictures provided on the charts.

Step 2. Remove the terminal from the connector.

1. Disengage the secondary locking device orterminal retainer.

a. Locking device must be disengaged before the terminal locking clip can be released and the terminal removed from the connector.

b. Use a miniature screwdriver or the terminal pickto unlock the secondary locking device.

2. Determine the primary locking system from the charts.

a. Lock located on terminal

b. Lock located on connector

c. Type of tool needed to unlock

d. Method of entry and operation



3. Remove terminal from connector by releasing the locking clip.

a. Push the terminal gently into the connector and hold it in this position.

b. Insert the terminal pick into the connector in the direction shown in the chart.

c. Move the locking clip to the un-lock position and hold it there.

NOTE: Do not apply excessive force to the terminal. Do not pry on the terminal with the pick.

d. Carefully withdraw the terminal from the connector by pulling the lead toward the rear of the connector.

NOTE: Do not use too much force. If the terminal does not come out easily, repeat steps (a.) through (d.).

4. Measure "nominal" size of the wire lead by placing a measuring device, such as a micrometer or Vernier Caliper, across the diameter of the insulation on the lead and taking a reading.

5. Select the correct replacement terminal, with lead, from the repair kit.



6. Cut the old terminal from the harness.

a. Use the new wire lead as a guide for proper length.

NOTE: If the length of wire removed is not approximately the same length as the new piece, the following problems may develop:

Too short - tension on the terminal, splice, or the connector, causing an open circuit.

Too long - excessive wire near the connector, may get pinched or abraded, causing a short circuit.

NOTE: If the connector is of a waterproof type, the rubber plug may be reused.

7. Strip insulation from wire on the harness and replacement terminal lead.

a. Strip length should be approximately 8 to 10 mm (3/8 in.).

NOTE: Strip carefully to avoid nicking or cutting any of the strands of wire.

NOTE: If heat shrink tube is to be used, it must be installed at this time, sliding it over the end of one wire to be spliced. (See Step 3, 4. B. 1. for instructions on how to use heat shrink tube.)

NOTE: If the connector is a waterproof type, the rubber plug should be installed on the terminal end at this time.



1. Select correct size of splice from the repair kit.

a. Size is based on the nominal size of the wire (three sizes are available).

Part Number Wire Size

Small 00204-34130 16-22 AWG1.0 - 0.2 mm

Medium 00204-34137 14-16 AWG2.0 - 1.0 mm

Large 00204-34138 10 - 12 AWG5.0 - 3.0 mm

2. Crimp the replacement terminal lead to the harness lead.

a. Insert the stripped ends of both the replacement lead and the harness lead into the splice, overlapping the wires inside the splice.

NOTE: Do not place insulation in the splice, only stripped wire.

b. Do not use position marked "INS".

The crimping tool has positions marked for insulated splices (marked "INS") that should not be used, as they will not crimp the splice tightly onto the wires.

c. Use only position marked "NON INS".

1. With the center of the splice correctly placed between the crimping jaws, squeeze the crimping tool together until the contact points of the crimper come together.

NOTE: Make sure the wires and the splice are still in the proper position before closing the crimping tool ends. Use steady pressure in making the crimp.

2. Make certain that the splice is crimped lightly.



3. Solder the completed splice using only rosin core solder.

a. Wires and splices must be clean.

b. A good mechanical joint must exist, because the solder will not hold the joint together.

c. Heat the joint with the soldering iron until the solder melts when pressed onto the joint.

d. Slowly press the solder into the hot splice on one end until it flows into the joint and out the other end of the splice.

NOTE: Do not use more solder than necessary to achieve a good connection. There should not be a "glob" of solder on the splice.

e. When enough solder has been applied, remove the solder from the joint and then remove the soldering iron.

4. Insulate the soldered splice using one of the following methods:

a. Silicon tape (provided in the wire repair kit)

1. Cut a piece of tape from the roll approximately 25 mm (1 in.) long.

2. Remove the clear wrapper from the tape.

NOTE: The tape will not feel "sticky" on either side.

3. Place one end of the tape on the wire and wrap the tape tightly around the wire. You should cover one-half of the previous wrap each time you make a complete turn around the wire. (When stretched, this tape will adhere to itself.)

4. When completed, the splice should be completely covered with the tape and the tape should stay in place. If both of these conditions are not met, remove the tape and repeat steps 1 through 4.

NOTE: If the splice is in the engine compartment or under the floor, or in an area where there might be abrasion on the spliced area, cover the silicon tape with vinyl tape.



b. Heat shrink tube (provided in the wire repair kit)

1. Cut a piece of the heat shrink tube that is slightly longer than the splice, and slightly larger in diameter than the splice.

2. Slide the tube over the end of one wire to be spliced. (THIS STEP MUST BE DONE PRIOR TO JOINING THE WIRES TOGETHER!)

3. Center the tube over the soldered splice.

4. Using a source of heat, such as a heat gun,gently heat the tubing until it has shrunk tightly around the splice.

NOTE: Do not continue heating the tubing after it has shrunk around the splice. It will only shrink a certain amount, and then stop. It will not continue to shrink as long as you hold heat to it, so be careful not to melt the insulation on the adjoining wires by trying to get the tubing to shrink further.

Step 4. Install the terminal into the connector.

1. If reusing a terminal, check that the locking clip is still in good condition and in the proper position.

a. If it is on the terminal and not in the proper position, use the terminal pick to gently bend the locking clip back to the original shape.

b. Check that the other parts of the terminal are in their original shape.



2. Push the terminal into the connector until you hear a "click".

NOTE: Not all terminals will give an audible "click".

a. When properly installed, pulling gently on the wire lead will prove the terminal is locked in the connector.

3. Close terminal retainer or secondary locking device.

a. If the connector is fitted with a terminal retainer, or a secondary locking device, return it to the lock position.

4. Secure the repaired wire to the harness.

a. If the wire is not in the conduit, or secured by other means, wrap vinyl tape around the bundle to keep it together with the other wires.




ASSIGNMENT NAME:

1. Explain which type of wire is used when current flow is high.

2. Explain what is mean by system polarity and how is it used today.

3. Explain how the colors of the wire insulation are used and give an example.

4. Explain how wire is sized, different sizing systems, and provide examples.

5. Name the correct type of solder used for electrical repair repair and why

6. Outline the procedure for “Tinning an Iron”.

7. List the rules for good soldering.

8. Outline in detail the correct procedure for splicing a new wire end on.

9. When and why is a heat gun used?

General

The battery is the primary "source" of electrical energy on Toyota vehicles. It stores chemicals, not electricity. Two different types of lead in an acid mixture react to produce an electrical pressure. This electrochemical reaction changes chemical energy to electrical energy.

Battery Functions

1. ENGINE OFF: Battery energy is used to operate the lighting and accessory systems.

2. ENGINE STARTING: Battery energy is used to operate the starter motor and to provide

current for the ignition system during cranking.

3. ENGINE RUNNING: Battery energy may be needed when the vehicle's electrical load requirements exceed the supply from the charging system.

In addition, the battery also serves as a voltage stabilizer, or large filter, by absorbing abnormal, transient voltages in the vehicle's electrical system. Without this protection, certain electrical or electronic components could be damaged by these high voltages.

Battery Types

1. PRIMARY CELL: The chemical reaction totally destroys one of the metals after a period of time. Small batteries for flashlights and radios are primary cells.

2. SECONDARY CELLS: The metals and acid mixture change as the battery supplies voltage. The metals become similar, the acid strength weakens. This is called discharging. By applying current to the battery in the opposite direction, the battery materials can be restored. This is called charging. Automotive lead-acid batteries are secondary cells.

3. WET-CHARGED: The lead-acid battery is filled with electrolyte and charged when it is built. During storage, a slow chemical reaction will cause self-discharge. Periodic charging is required. For Toyota batteries, this is every 5 to 7 months.

4. DRY-CHARGED: The battery is built, charged, washed and dried, sealed, and shipped without electrolyte. It can be stored for 12 to .18 months. When put into use, it requires adding electrolyte and charging.

5. LOW-MAINTENANCE: Most batteries for Toyota vehicles are considered low-maintenance batteries. Such batteries are built to reduce internal heat and water loss. The addition of water should only be required every 15,000 miles or so.

BATTERIES


Construction

1. CASE: Container which holds and protects all battery components and electrolyte, separates cells, and provides space at the bottom for sediment (active materials washed off plates). Translucent plastic cases allow checking electrolyte level without removing vent caps.

2. COVER: Permanently sealed to the top of the case; provides outlets for terminal posts, vent holes for venting of gases and for battery maintenance (checking electrolyte, adding water).

3. PLATES: Positive and negative plates have a grid framework of antimony and lead alloy. Active material is pasted to the grid ... brown-colored lead dioxide (Pb02) on positive plates, gray-colored sponge lead (Pb) on negative plates. The number and size of the plates determine current capability ... batteries with large plates or many plates produce more current than batteries with small plates or few plates.

4. SEPARATORS: Thin, porous insulators (woven glass or plastic envelopes) are placed between positive and negative plates. They allow passage of electrolyte, yet prevent the plates from touching and shorting out.

5. CELLS: An assembly of connected positive and negative plates with separators in between is called a cell or element. When immersed in electrolyte, a cell produces about 2.1 volts

(regardless of the number or size of plates). Battery cells are connected in series, so the number of cells determines the battery voltage. A "1 2 - volt" battery has six cells.

6. CELL CONNECTORS: Heavy, cast alloy metal straps are welded to the negative terminal of one cell and the positive terminal of the adjoining cell until all six cells are connected in series.

7. CELL PARTITIONS: Part of the case, the partitions separate each cell.

8. TERMINAL POSTS: Positive and negative posts (terminals) on the case top have thick, heavy cables connected to them. These cables connect the battery to the vehicle's electrical system (positive) and to ground (negative).

9. VENT CAPS: Types include individual filler plugs, strip-type, or box-type. They allow controlled release of hydrogen gas during charging (vehicle operation). Removed, they permit checking electrolyte and, if necessary, adding water.

10. ELECTROLYTE: A mixture of sulfuric acid (H2SO4) and water (H2O). It reacts chemically with the active materials in the plates to create an electrical pressure (voltage). And, it conducts the electrical current produced by that pressure from plate to plate. A fully charged battery will have about 36% acid and 64% water.

BATTERIES


CELL THEORYA lead-acid cell works by a simple principle: when two different metals are immersed in an acid solution, a chemical reaction creates an electrical pressure.One metal is brown-colored lead dioxide (Pb02). It has a positive electrical charge. The other metal is gray colored sponge lead (Pb). It has a negative electrical charge. The acid solution is a mixture of sulfuric acid (H2SO4) and water (H20). It is called

electrolyte.If a conductor and a load are connected between the two metals, current will flow. This discharging will continue until the metals become alike and the acid is used up. The action can be reversed by sending current into the cell in the opposite direction. This charging will continue until the cell materials are restored to their original condition.

BATTERIES


ELECTROCHEMICAL REACTIONA lead-acid storage battery can be partially discharged and recharged many times. There are four stages in this discharging/charging cycle.

1. CHARGED: A fully charged battery contains a negative plate of sponge lead (Pb), a positive plate of lead dioxide (Pb02), and electrolyte of sulfuric acid (H2SO4) and water (H20).

2. DISCHARGING: As the battery is discharging, the electrolyte becomes diluted and the plates become sulfated. The electrolyte divides into hydrogen (H2) and sulfate(S04) . The hydrogen (H2) combines with oxygen (0) from the positive plate to form more water (H20). The sulfate combines with the lead (Pb) in both plates to form lead sulfate (PbS04)

3. DISCHARGED: In a fully discharged battery, both plates are covered with lead sulfate (PbSO4) and the electrolyte is diluted to mostly water (H2O).

4. CHARGING: During charging, the chemical action is reversed. Sulfate (S04) leaves the plates and combines with hydrogen (H2) to become sulfuric acid (H2SO4). Free oxygen (02) combines with lead (Pb) on the positive plate to form lead dioxide (Pb02). Gassing occurs as the battery nears full charge, and hydrogen bubbles out at the negative plates, oxygen at the positive.

BATTERIES


Capacity RatingsThe battery must be capable of cranking the engine and providing adequate reserve capacity. Its capacity is the amount of electrical energy the battery can deliver when fully charged. Capacity is determined by the size and number of plates, the number of cells, and the strength and volume of electrolyte.

The most commonly used ratings are:

• Cold Cranking Amperes (CCA)

• Reserve Capacity (RC)

• Amp-Hours (AH)

• Power (Watts)

COLD-CRANKING AMPERES (CCA)The battery's primary function is to provide energy to crank the engine during starting. This requires a large discharge in a short time. The CCA Rating specifies, in amperes, the discharge load a fully charged battery at 0˚F (-1 7.8˚C) can deliver for 30 seconds while maintaining a voltage of at least 1.2 volts per cell (7.2 volts total for a 12-volt battery). Batteries used on various Toyota vehicles have CCA ratings ranging from 350 to 560 amps.

RESERVE CAPACITY (RC)The battery must provide emergency energy for ignition, lights, and accessories if the vehicle's charging system fails. This requires adequate capacity at normal temperatures for a certain amount of time. The RC Rating specifies, in minutes, the length of time a fully charged battery at 80˚F (26.7'C) can be discharged at 25 amps while maintaining a voltage of at least 1.75 volts per cell (10.5 volts total for a 12-volt battery). Batteries used on various Toyota vehicles have RC ratings ranging from 55 to 115 minutes.

AMP-HOURS (AH)The battery must maintain active materials on its plates and adequate lasting power under light-load conditions. This method of rating batteries is also called the 20-hour discharge rating. Original equipment batteries are rated in amp-hours. The ratings of these batteries are listed in the parts microfiche. The Amp-Hour Rating specifies, in amphours, the current the battery can provide for 20 hours at 80˚F (26.7˚C) while maintaining a voltage of at least 1.75 volts per cell (10.5 volts total for a 12-volt battery). For example, a battery that can deliver 4 amps for 20 hours is rated at 80 amp-hours (4 x 20 = 80). Batteries used on various Toyota vehicles have AH ratings ranging from 40 to 80 amp-hours.

POWER (WATTS)The battery's available cranking power may also be measured in watts. The Power Rating, in watts, is determined by multiplying the current available by the battery voltage at 0˚F (-1 7.8˚C). Batteries used on various Toyota vehicles have power ratings ranging from 2000 to 4000 watts.

BATTERIES


FACTORS AFFECTING CHARGINGFive factors affect battery charging by increasing its internal resistance and CEMF (counter-electromotive force produced by the electrochemical reaction):

1. TEMPERATURE: As the temperature decreases the electrolyte resists charging. A cold battery will take more time to charge; a warm battery, less time. Never attempt to charge a frozen battery.

2. STATE-OF-CHARGE: The condition of the battery's active materials will affect charging. A battery that is severely discharged will have hard sulfate crystals on its plates. The vehicle's charging system may charge at too high of a rate to remove such sulfates.

3. PLATE AREA: Small plates are charged faster than large plates. When sulfation covers most of the plate area, the charging system may not be able to restore the battery.

4. IMPURITIES: Dirt and other impurities in the electrolyte increase charging difficulty.

5. GASSING: Hydrogen and oxygen bubbles form at the plates during charging. As these bubble out, they wash away active material, cause water loss, and increase charging difficulty.

BATTERIES


BATTERIES


Diagnosis and Testing

All batteries require routine maintenance to identify and correct problems caused by physical abuse and low electrolyte levels. A visual inspection can identify such physical problems. A state-of-charge test checks the electrolyte strength. And, electrical testing identifies overcharging or undercharging problems. These tests include a capacity, or heavy-load, test.

SAFETY FIRST!

When testing or servicing a battery, safety should be your first consideration. The electrolyte contains sulfuric acid. It can eat your clothes. It can burn your skin. It can blind you if it gets in your eyes. It can also ruin a car's finish or upholstery. If electrolyte is splashed on your skin or in your eyes, wash it away immediately with large amounts of water. If electrolyte is spilled on the car, wash it away with a solution of baking soda and water.

When a battery is being charged, either by the charging system or by a separate charger, gassing will occur. Hydrogen gas is explosive. Any flame or spark can ignite it. If the flame travels into the cells, the battery may explode.

Safety precautions include:

• Wear gloves and safety glasses.

• Remove rings, watches, other jewelry.

• Never use spark-producing tools near a battery.

• Never lay tools on the battery.

• When removing cables, always remove the ground cable first.

• When connecting cables, always connect the ground cable last.

• Do not use the battery ground terminal when checking for ignition spark.

• Be careful not to get electrolyte in your eyes or on your skin, the car finish, or your clothing.

• If you have to mix battery electrolyte, pour the acid into the water - not the water into the acid.

• Always follow the recommended procedures for battery testing and charging and for jump starting an engine.

CARE OF ELECTRONICS

Disconnecting the battery will erase the memory onelectronic devices. Write down trouble codes and

programmed settings before disconnecting the battery.

Also, to prevent damage to electronic components:

• Never disconnect the battery with the ignition ON.

• Never use an electric welder without the battery cables disconnected.

• Never reverse battery polarity.

BATTERIES


VISUAL INSPECTION

Battery service should begin with a thorough visual inspection. This may reveal simple, easily corrected problems, or problems that might require battery replacement.

1 . Check for cracks in the battery case and for broken terminals. Either may allow electrolyte leakage. The battery must be replaced.

2. Check for cracked or broken cables or connections. Replace, as needed.

3. Check for corrosion on terminals and dirt or acid on the case top. Clean the terminals and case top with a mixture of water and baking soda or ammonia. A wire brush is needed for heavy corrosion on the terminals.

4. Check for a loose battery hold-down and loose cable connections. Tighten, as needed.

5. Check the level of electrolyte. The level can be viewed through the translucent plastic case or by removing the vent caps and looking directly into each cell. The proper level is 1/2" above the separators. If necessary, add distilled water to each low cell. Avoid overfilling. When water is added, always charge the battery to make sure the water and acid mix.

6. Check for cloudy or discolored electrolyte caused by overcharging or vibration. This could cause high self discharge. The problem should be corrected and the battery replaced.

7. Check the condition of plates and separators. Plates should alternate dark (+) and light (-). If all are light, severe undercharging is indicated. Cracked separators may allow shorts. The battery should be replaced. An undercharging problem should be corrected.

BATTERIES


8. Check the tension and condition of the alternator drive belt. A loose belt must be tightened. It will prevent proper charging. A belt too tight will reduce alternator life. It should be loosened to specs. A frayed or glazed belt will fail during operation. Replace it.

NOTE: Approved Equipment tension gauge: Nippondenso, BTG-20 (SST) Borroughs BT-33-73F

9. Check for battery drain or parasitic loads using an ammeter. Connect the ammeter in series between the battery negative terminal and ground cable connector. Toyota vehicles typically show less than .020 amp of current to maintain electronic memories ... a reading of more than .035 amp is unacceptable. If the ammeter reads more than .035 amp, locate and correct the cause of excessive battery drain.

10. Check for battery discharge across the top of the battery using a voltmeter. Select the low voltage scale on the meter, connect the negative (black) test lead to the battery's negative post, and connect the positive (red) test lead to the top of the battery case. If the meter reading is more than 0.5 volt, clean the case top using a solution of baking soda and water.

BATTERIES


STATE-OF-CHARGE TESTThe state-of-charge test checks the battery's chemical condition. One method uses a hydrometer to measure the specific gravity of the electrolyte. Another method uses a digital voltmeter to check the battery's open circuit voltage and, for a general indication of the battery's condition, check the indicator eye (if the battery has one) or check the headlamp brightness during starting.

Specific GravitySpecific gravity means exact weight. The hydrometer compares the exact weight of electrolyte with that of water. Strong electrolyte in a charged battery is heavier than weak electrolyte in a discharged battery.

By weight, the electrolyte in a fully charged battery is about 36% acid and 64% water. The specific gravity of water is 1.000. The acid is 1.835 times heavier than water, so its specific gravity is 1.835. The electrolyte mixture of water and acid has a specific gravity of 1.270 is usually stated as "twelve and seventy."By measuring the specific gravity of the electrolyte, you can tell if the battery is fully charged, requires charging, or must be replaced. It can tell you if the battery is charged enough for the capacity, or heavy-load test.

TEST PROCEDURE: The following steps outline a typical procedure for performing a state-of-charge test:1 . Remove vent caps or covers from the battery cells.2. Squeeze the hydrometer bulb and insert the pickup tube into the cell closest to the battery's positive (+) terminal.3. Slowly release the bulb to draw in only enough

electrolyte to cause the float to rise. Do not remove the tube from the cell.

4. Read the specific gravity indicated on the float. Be sure the float is drifting free, not in contact with the sides of top of the barrel. Bend down to read the hydrometer a eye level. Disregard the slight curvature of liquid on the float.

5. Read the temperature of the electrolyte.6. Record your readings and repeat the procedure for the remaining cells.

TEMPERATURE CORRECTION: The specific gravity changes with temperature. Heat thins the liquid, and lowers the specific gravity. Cold thickens the liquid, and raises the specific gravity. Hydrometers are accurate at 80-F (26.7˚C). If the electrolyte is at any other temperature, the hydrometer readings must be adjusted. Most hydrometers have a built-in thermometer and conversion chart. Refer to the temperature correction chart. For each 1 O˚F (5.5˚C) above 80˚F (26.7˚C), ADD 0.004 to your reading.

BATTERIES


TEST RESULTS: Specific gravity readings tell a lot about battery condition.

1. A fully charged battery will have specific gravity readings around 1.265.

2. Specific gravity readings below 1.225 usually mean the battery is run down and must be charged.

3. Readings around 1.190 indicate that sulfation is about to begin. The battery must be charged.

4. Readings of 1.155 indicate severe discharge. Slow charging is required to restore active materials.

5. Readings of 1.120 or less indicate that the battery is completely discharged. It may require replacement, but slow charging may restore some batteries in this condition.

6. A difference of 50 points (0.050) or more between one or more cells indicates a defective battery. It should be replaced.

7. When the specific gravity of all cells is above 1.225 and the variation between cells is less than 50 points, the battery can be tested under load.

Open-Circuit VoltageAn accurate digital voltmeter is used to check the battery's open-circuit voltage:

1 . If the battery has just been charged, turn on the headlamps for one minute to remove any surface charge.

2. Turn headlamps off and connect the voltmeter across the battery terminals.

3. Read the voltmeter. A fully charged battery will have an open-circuit voltage of at least 12.6 volts. A dead battery will have an open-circuit voltage of less than 12.0 volts.

Indicator EyeToyota original-equipment batteries have an indicator eye for electrolyte level and specific gravity. If the eye shows red, the electrolyte level is low or the battery is severely discharged. If some blue is showing, the level is okay and the battery is at least 25% charged.

NOTE: The indicator eye should be used only as a general indication of electrolyte level and strength.

BATTERIES


HEAVY-LOAD TESTWhile an open circuit voltage test determines the battery's state of charge, it does not measure the battery's ability to deliver adequate cranking power. A capacity, or heavy-load, test does. A Sun VAT-40 tester is used. If another type of tester is used, follow the manufacturer's recommended procedure.

The following steps outline a typical procedure for load testing a battery:

1. Test the open circuit voltage. The battery must be at least half charged. If the open circuit voltage is less than 12.4v, charge the battery.

2. Disconnect the battery cables, ground cable first.3. Prepare the tester: • Rotate the Load Increase control to OFF. • Check each meter's mechanical zero. Adjust, if necessary. • Connect the tester Load Leads to the battery

terminals; RED to positive, BLACK to negative. • Set Volt Selector to INT 18V. Tester voltmeter

should indicate battery open-circuit voltage.

NOTE: Battery open-circuit voltage should be at least 12.4 volts (75% charged). If not, the battery requires charging.

• Set Test Selector to #2 CHARGING. • Adjust ammeter to read ZERO using the electrical Zero Adjust control.4. Connect the clamp-on Amps Pickup around either

tester load cable (disregard polarity).5. Set the Test Selector Switch to #1 STARTING.6. Load the battery by turning the Load Increase

control until the ammeter reads 3 times the amp-hour (AH) rating or one-half the cold-cranking ampere (CCA) rating.

7. Maintain the load for no more than 15 seconds and note the voltmeter reading.

8. Immediately turn the Load Increase control OFF.9. If the voltmeter reading was 10.0 volts or more, the

battery is good. If the reading is 9.6 to 9.9 volts, the battery is serviceable, but requires further testing. Charge and re-test. If the reading was below 9.6 volts, the battery is either discharged or defective.

NOTE: Test results will vary with temperature. Low temperatures will reduce the reading. The battery should be at operating temperature.

BATTERIES


Battery ServiceBattery service procedures include charging, cleaning, jump starting, and replacement. Follow the recommended procedures.

CHARGINGA battery in good condition may occasionally fail to crank the engine fast enough to make it start. In such cases, the battery may require charging.

All battery chargers operate on the same principle: an electric current is applied to the battery to reverse the chemical action in the cells. Never connect or disconnect leads with the charger turned ON. Follow the battery charger manufacturer's instructions. And, do not attempt to charge a battery with frozen electrolyte.

When using a battery charger, always disconnect the battery ground cable first. This will minimize the possibility of damage to the alternator or to electronic components. Otherwise, use a charger with polarity protection that prevents reverse charging.

The battery can be considered fully charged when all cells are gassing freely and when there is no change in specific gravity readings for more than one hour.

BATTERIES


Fast ChargingFast charging is used to charge the battery for a short period of time with a high rate of current. Fast charging may shorten battery life. If time allows, slow charging is preferred. Some low maintenance batteries cannot be fast charged.

1. Preparation for charging. • Clean dirt, dust, or corrosion off the battery; if

necessary, clean the terminals. • Check the electrolyte level and add distilled

water if needed. • If the battery is to be charged while on the

vehicle, be sure to disconnect both (-) (+) terminals.

2. Determine the charging current and time for fast charging.

• Some chargers have a test device for determining the charging current and required time.

• If the charger does not have a test device, refer to the chart below to determine current and time.

3. Using the charger: • Make sure that the main switch and timer switch are OFF and the current adjust switch is at the

minimum position. • Connect the positive lead of the charger to the battery positive terminal (+) and the negative

lead of the charger to the battery negative terminal (-).

• Connect the charger's power cable to the electric outlet.

• Set the voltage switch to the correct battery voltage.

• Set the main switch at ON. • Set the timer to the desired time and adjust the

charging current to the predetermined amperage.

4. After the timer is "off," check the charged condition using a voltmeter.

• Correct Voltage: 12.6 volts or higher.

If the voltage does not increase, or if gas is not emitted no matter how long the battery is charged, there may be a problem with the battery, such as an internal short.

5. When the voltage reaches the proper reading: • Set the current adjust switch to minimum. • Turn off the main switch of the charger. • Disconnect the charger cables from the battery terminals. • Wash the battery case to clean off the acid emitted.

Slow ChargingHigh charging rates are not good for completely charging a battery. To completely charge a battery, slow charging with a low current is required.Slow charging procedures are the same as those for fast charging, except for the following:

1. The maximum charging current should be less than 1 1/10th of the battery capacity. For instance, a 40 AH battery should be slow charged at 4 amps or less.

2. Set the charger switch to the slow position (if provided).

3. Readjust the current control switch from time to time while charging.

4. As the battery gets near full charge, hydrogen gas is emitted. When there is no further rise in battery voltage for more than one hour, the battery is completely charged.

• Battery Voltage: 12.6 volts or higher

BATTERIES


CLEANINGCleaning the battery will aid your visual inspection and reduce the possibility of current leakage. The battery case can be cleaned with a brush and diluted ammonia or soda solution. Avoid getting the solution in the cells. The battery terminals and cable connections can be cleaned with the cleaning tool (brush) made for that purpose. Remove all corrosion and oxidation, both common causes of high resistance.

JUMP STARTINGWhen jump starting a dead battery with a booster battery, proper connections prevent sparks. First, connect the two positive terminals. Then, connect one end of the jumper cable to the negative terminal of the booster battery. And, connect the other end to a good ground away from the dead battery. If a spark occurs, it won't be near the battery.

BATTERY REPLACEMENTIf a battery requires replacement: use a cable puller to remove terminal clamps; unfasten the battery hold-down; lift the battery from its carrier with the proper tool; wash and paint corroded parts; replace any damaged parts of the hold-down, support tray, or cables; and select and install a battery of the proper size and capacity rating.

Taken with permission from the Toyota Basic Electrical Course #622,

BATTERIES


SELF TESTThis brief self-test will help you measure your understanding of The Battery. The style is the same as that used for A.S.E. certification tests. The answers to this self test are shown on next page.

1. The amount of current a battery can produce is controlled by the:

A. plate thicknessB. plate surface areaC. strength of acidD. discharge of load

2. How many volts are produced in each cell of a battery?

A. 2.1B. 6. 0C. 9.6D. 12.0

3. The plates of a discharged battery are:

A. two similar metals in the presence of an electrolyte

B. two similar metals in the presence of water C. two dissimilar metals in the presence of an electrolyte D. two dissimilar metals in the presence of

water

4. A battery's reserve capacity is measured in:

A. amperesB. waftsC. amp-HoursD. minutes

5. Severe battery undercharging is indicated if:

A. active materials are washed off the platesB. the terminals are corrodedC. the plates (+ and -) are both very light

coloredD. the electrolyte is cloudy

6. To check for battery drain, you would connect an ammeter between the:

A. battery and alternatorB. battery and (-) terminalsC. battery terminal and ground cableD. battery terminal and ground cable

7. What is the state of charge of a battery that has a specific gravity of 1.190 at 80˚F (26.7'C)?

A. Completely dischargedB. About 1/2 chargedC. About 3/4 chargedD. Fully charged

8. A battery heavy-load test discharges the battery for:

A. 5 secondsB. 10 secondsC. 15 secondsD. 20 seconds

9. When performing a battery capacity test on a 12-volt battery, the voltage should not fall below:

A. 12.0 voltsB. 10.6 voltsC. 9.6 voltsD. 8.6 volts

10. The preferred method of recharging a "dead" battery is:

A. fast chargingB. slow chargingC. cycling the batteryD. with a VAT-40

BATTERIES


SELF-TEST ANSWERS

For the preceding self-test on The Battery, the following best complete the sentence or answer the question. In cases where you may disagree with the choice - or may simply want to reinforce your understanding - please review the appropriate workbook page or pages noted.

1 . "B" - The number and size of the plates determine current capability. (Page 2.)

2. "A" - When immersed in electrolyte, a cell produces about 2.1 volts (regardless of the number of size of plates). (Page 2.)

3. "B" - In a fully discharged battery, both plates are covered with lead sulfate and the electrolyte is diluted to mostly water. (Page 4.)

4. "D" - The Reserve Capacity rating is the length of time, in minutes, a fully charged battery at 80'F (26.70C) can be discharged at 25 amps while maintaining a voltage of at least 1.75 volts per cell. (Page 5.)

5. "C" - Plates should alternate dark (+) and light It all are light, severe undercharging is indicated. (Page 9.)

6. "D" - Check for battery drain using an ammeter between the battery negative terminal and ground cable connector. (Page 10.)

7. "B" - Specific gravity readings around 1.190 indicate that sulfation is about to begin. The battery is about 50% charged, and requires charging. (Page 12.)

8. "C" - In a battery load test, maintain the load for no more than 15 seconds and note the voltmeter reading. (Page 13.)

9. "C" - In a battery capacity or heavy-load test, if the voltmeter reading falls below 9.6 volts, the battery is either discharged or defective. (Page 13.)

10. "B" - Slow charging is preferred. (Page 15.)

BATTERIES


BATTERIES

ASSIGNMENT NAME:

1. Describe the basic construction of a lead-acid battery.

2. Explain what materials are used to make up the: positive plate, negative plate, and electrolyte.

3. Describe the basic chemical operation of a single cell that makes a battery.

4. List the voltage output of both a single battery cell and a six cell automotive battery. Be exact.

5. Explain the four basic battery “capacity ratings” systems.

6. List the gases that are produced during the charging process from both the positive andthe negative plates.

7. Explain why repeated “overcharging” or “cycling” is harmful to a battery.

8. List the three basic battery tests / inspections that can be performed.

9. List ten (10) items inspected while performing a “visual inspection”.

10. Explain the terms “battery drain” and “parasitic loads”.

11. Describe the procedure of checking parasitic drain on a car.

12. List the maximum parasitic drain allowed.

13. Describe why and how baking soda is used on an automotive battery.

14. List two methods of checking a battery’s “state of charge.

15. List the specific gravity readings of a battery that has the following states of charge: 100%, 50%, 0%.

16. Explain the term “specific gravity” and how it is measured.

17. List the open circuit voltages of a battery with the following states of charge 100%, 50%, 0%.

18. Describe the “open circuit voltage” test procedure.

19. What is the minimum charge a battery needs to perform a Heavy Load Test.

20. Explain in detail the “Heavy Load” or “Capacity” test procedure.

21. What is the maximum time a Heavy Load Test should be performed?

22 How much of a load is placed on a battery that has a 500 CCA rating?

23. What action should be taken if battery voltage drops to 8.7 volts during a heavy load test? What if the voltage was 10.3 volts?

General

Starting the engine is possibly the most important function of the vehicle's electrical system. The starting system performs this function by changing electrical energy from the battery to mechanical energy in the starting motor. This motor then transfers the mechanical energy, through gears, to the flywheel on the engine's crankshaft. During cranking, the flywheel rotates and the air-fuel mixture is drawn into the cylinders, compressed, and ignited to start the engine. Most engines require a cranking speed of about 200 rpm.

Toyota Starting SystemsTwo different starting systems are used on Toyota vehicles. Both systems have two separate electrical circuits ... a control circuit and a motor circuit. One has a conventional starting motor.

This system is used on most older-model Toyotas. The other has a gear reduction starting motor. This system is used on most current Toyotas. A heavy-duty magnetic switch, or solenoid, turns the motor on and off. It is part of both the motor circuit and the control circuit.

Both systems are controlled by the ignition switch and protected by a fusible link. On some models, a starter relay is used in the starter control circuit. On models with automatic transmission, a neutral start switch prevents starting with the transmission in gear. On models with manual transmission, a clutch switch prevents starting unless the clutch is fully depressed. On 4WD Truck and 4-Runner models, a safety cancel switch allows starting on hills without the clutch depressed. It does so by establishing an alternate path to ground.

TOYOTA STARTING SYSTEMS


Starting System Operation



Starting Motor Construction

GENERAL

The starter motors used on Toyota vehicles have a magnetic switch that shifts a rotating gear (pinion gear) into and out of mesh with the ring gear on the engine flywheel. Two types of motors are used: conventional and gear reduction. Both are rated by power output in kilowatts (KW) ... the greater the output, the greater the cranking power.

CONVENTIONAL STARTER MOTOR The conventional starter motor contains the components shown. The pinion gear is on the same shaft as the motor armature and rotates

at the same speed. A plunger in the magnetic switch (solenoid) is connected to a shift lever. When activated by the plunger, the shift lever pushes the pinion gear and causes it to mesh with the flywheel ring gear. When the engine starts, an over-running clutch disengages the pinion gear to prevent engine torque from ruining the starting motor.

This type of starter was used on most 1975 and older Toyota vehicles. It is currently used on certain Tercel models. Typical output ratings are 0.8, 0.9, and 1.0KW. In most cases, replacement starters for these older motors are gear-reduction motors.



GEAR-REDUCTION STARTER MOTOR

The gear-reduction starter motor contains the components shown. This type of starter has a compact, high-speed motor and a set of reduction gears. While the motor is smaller and weighs less than conventional starting motors, it operates at higher speed. The reduction gears transfer this torque to the pinion gear at 1/4 to 1/3 the motor speed. The pinion gear still rotates faster than the gear on a conventional starter and with much greater torque (cranking power).

The reduction gear is mounted on the same shaft as the pinion gear. And, unlike in the conventional

starter, the magnetic switch plunger acts directly on the pinion gear (not through a drive lever) to push the gear into mesh with the ring gear.

This type of starter was first used on the 1973 Corona MKII with the 4M, six cylinder engine. It is now used on most 1975 and newer Toyotas. Ratings range from 0.8KW on most Tercels and some older models to as high as 2.5KW on the diesel Corolla, Camry and Truck. The cold-weather package calls for a 1.4KW or 1.6KW starter, while a 1.0KW starter is common on other models.

The gear-reduction starter is the replacement starter for most conventional starters.



Starting Motor Operation

CONVENTIONAL STARTER MOTOR

IGNITION SWITCH IN "ST"

• Current flows from the battery through terminal "50" to the hold-in and pull-in coils. Then, from the pull-in coil, current flows through terminal "C" to the field coils and armature coils.

• Voltage drop across the pull-in coil limits the current to the motor, keeping its speed low.

• The solenoid plunger pulls the drive lever to mesh the pinion gear with the ring gear.

• The screw spline and low motor speed help the gears mesh smoothly.

PINION AND RING GEARS ENGAGED

• When the gears are meshed, the contact plate on the plunger turns on the main switch by closing the connection between terminals "30" and "C."

• More current goes to the motor and it rotates with greater torque (cranking power).

• Current no longer flows in the pull-in coil. The plunger is held in position by the hold-in coil's magnetic force.

IGNITION SWITCH IN "ON"

• Current no longer flows to terminal "50," but the main switch remains closed to allow current flow from terminal "C" through the pull-in coil to the hold-in coil.

• The magnetic fields in the two coils cancel each other, and the plunger is pulled back by the return spring.

• The high current to the motor is cut off and the pinion gear disengages from the ring gear.

• A spring-loaded brake stops the armature.



GEAR-REDUCTION STARTER MOTOR

IGNITION SWITCH IN "ST"

• Current flows from the battery through terminal "50" to the hold-in and pull-in coils. Then, from the pull-in coil, current flows through terminal "C" to the field coils and armature coils.

• Voltage drop across the pull-in coil limits the current to the motor, keeping its speed low.

• The magnetic switch plunger pushes the pinion gear to mesh with the ring gear.

• he screw and low motor speed help the gears mesh smoothly.

PINION AND RING GEARS ENGAGED

• When the gears are meshed, the contact plate on he plunger turns on the main switch by closing the connection between terminals "30" and "C."

• More current goes to the motor and it rotates with greater torque.

• Current no longer flows in the pull-in coil. The plunger is held in position by the hold-in coil's magnetic force.

IGNITION SWITCH IN "ON"

• Current no longer flows to terminal "50," but the main switch remains closed to allow current flow from terminal "C" through the pull-in coil to the hold-in coil.

• The magnetic fields in the two coils cancel each other, and the plunger is pulled back by the return spring.

• The high current to the motor is cut off and the pinion gear disengages from the ring gear.

• The armature has less inertia than the one in a conventional starter. Friction stops it, so a brake is not needed.



OVER-RUNNING CLUTCH

Both types of starter motors used on Toyota starting systems have a one-way clutch, or over-running clutch. This clutch prevents damage to the starter motor once the engine has been started. It does so, by disengaging its housing (which rotates with the motor armature) from an inner

race which is combined with the pinion gear. Spring loaded wedged rollers are used.

Without an over-running clutch, the starter motor would be quickly destroyed if engine torque was transferred through the pinion gear to the armature.




The starting system requires little maintenance. Simply, keep the battery fully charged and all electrical connections clean and tight.

Diagnosis of starting system problems is relatively easy. The system combines electrical and mechanical components. The cause of a starting problem may be electrical (e.g., faulty switch) or mechanical (e.g., wrong engine oil or a faulty flywheel ring gear).

Specific symptoms of starting system problems include:

• The engine will not crank;

• The engine cranks slowly;

• The starter keeps running;

• The starter spins, but the engine will not crank; and,

• The starter does not engage or disengage properly.

For each of these problems, refer to the chart below for the possible causes and needed actions. Diagnosis starts with a thorough visual inspection. Testing includes: a starter motor current draw test, starter circuit voltage drop tests, operational and continuity checks of control components, and starter motor bench tests.



VISUAL INSPECTION

A visual inspection of the starting system can uncover a number of simple, easy-to-correct problems.

• SAFETY FIRST: The same safety considerations used in checking the battery apply here. Remove rings, wristwatch, other jewelry that might contact battery terminals. Wear safety glasses and protective clothing. Be careful not to spill electrolyte and know what to do if electrolyte gets in your eyes, on your skin or clothing, or on the car's finish. Write down programmed settings on electronic components. Avoid causing sparks.

• STARTING PERFORMANCE: Check the starting performance. Problem symptoms, possible causes, and needed actions are shown in the chart on the previous page.

• BATTERY CHECKS: Inspect the battery for corrosion, loose connections. Check the electrolyte level, condition of the plates and separators, and state of charge (specific gravity or open-circuit voltage). Load test the battery. It must be capable of providing at least 9.6 volts during cranking.

STARTER CABLES: Check the cable condition and connections. Insulation should not be worn or damaged. Connections should be clean and tight.

STARTER CONTROL CIRCUIT: Check the operation of the ignition switch. Current should be supplied to the magnetic switch when the ignition is "on" and the clutch switch or neutral start switch is closed. Faulty parts that prevent cranking can be located using a remote-control starter switch and a jumper wire. Use the "split half" diagnosis method. Ohmmeter checks can also identify component problems.



CURRENT DRAW TESTA starter current draw test provides a quick check of the entire starting system. With the Sun VAT-40 tester, it also checks battery's cranking voltage. If another type of tester is used, follow the manufacturer's recommended procedure.

The starting current draw and cranking voltage should meet the specifications listed for the Toyota model being tested. Typical current draw specs are 130-150 amps for 4-cylinder models and 175 amps for 6-cylinder models. Cranking voltage specs range from 9.6 to 11 volts. Always refer to the correct repair manual. Only perform the test with the engine at operating temperature.

The following steps outline a typical procedure for performing a current draw test on a starting system:

1. This test should be made only with a serviceable battery. The specific gravity

readings at 800˚F should average at least 1. 190 (50% charged). Charge the battery, if necessary.

2. Prepare the tester:

• Rotate the Load Increase control to OFF.

• Check each meter's mechanical zero. Adjust, if necessary.

• Connect the tester Load Leads to the battery terminals; RED to positive, BLACK to negative.

NOTE: Battery open-circuit voltage should be at least 12.2 volts (50% charged). If not, the battery requires charging.

• Set Volt Selector to INT 18V. Tester voltmeter should indicate battery open-circuit voltage.

• Set Test Selector to #2 CHARGING.

• Adjust ammeter to read ZERO using the electrical Zero Adjust control.

3. Connect the clamp-on Amps Pickup around the battery ground cable or cables.

4. Make sure all lights and accessories are off and vehicle doors are closed.

5. Set the Test Selector switch to #1 STARTING.

6. Disable the ignition so the engine does not start during testing.

7. Crank the engine, while observing the tester ammeter and voltmeter.

• Cranking speed should be normal (200-250 rpm).

• Current draw should not exceed the maximum specified.

• Cranking voltage should be at or above the minimum specified.

8. Restore the engine to starting condition and remove tester leads.

TEST RESULTS: High current draw and low cranking speed usually indicate a faulty starter. High current draw may also be caused by engine problems. A low cranking speed with low current draw, but high cranking voltage, usually indicates excessive resistance in the starter circuit. Remember that the battery must be fully charged and its connections tight to insure accurate results.



VOLTAGE-DROP TESTS

Voltage-drop testing can detect excessive resistance in the starting system. High resistance in the starter motor circuit (power side or ground side) will reduce current to the starting motor. This can cause slow cranking speed and hard starting. High resistance in the starter control circuit will reduce current to the magnetic switch. This can cause improper operation or no operation at all.

A Sun VAT-40 tester or separate voltmeter can be used. The following steps outline a typical procedure for performing voltage-drop tests on the starting system:

Motor Circuit (insulated Side)1. If using the Sun VAT-40, set the Volt Selector to

EXT 3V. For other voltmeters, use a low scale.

2. Connect the voltmeter leads ... RED to the battery positive (+) terminal, BLACK to terminal "C" on the starter motor magnetic switch.

3. Disable the ignition so the engine cannot start during testing.

NOTE: On models with the Integrated Ignition Assembly, disconnect the "IIA" plug. On others, disconnect the power plug to the remote igniter assembly (black-orange wire).

4. Crank the engine and observe the voltmeter. Less than 0.5 volt indicates acceptable resistance. More than 0.5 volt indicates excessive resistance. This could be caused by a damaged cable, poor connections, or a defective magnetic switch.

5. If excessive resistance is indicated, locate the cause. Acceptable voltage drops are 0.3 volt across the magnetic switch, 0.2 volts for the cable, and zero volts for the cable connection. Repair or replace components, as needed.



Motor Circuit (Ground Side) 1. Connect the voltmeter leads ... RED to the starter

motor housing, BLACK to the battery ground (-) terminal.

2. Crank the engine and observe the voltmeter. Less than 0.2 volt indicates acceptable resistance. More than 0.2 volt indicates excessive resistance. This could be caused by a loose motor mount, a bad battery ground, or a loose connection. Repair or replace components as necessary. Make sure engine-to-body ground straps are secure.

Control Circuit 1. Connect the voltmeter leads ... RED to the

battery positive (+) terminal, BLACK to terminal "50" of the starting motor.

2. On vehicles with automatic transmission, place the lever in Park or Neutral. On vehicles with manual transmission, depress the clutch.

(NOTE: A jumper wire could be used to bypass either of these switches).

3. Crank the engine and observe the voltmeter. Less than .5 volt is acceptable. If the current draw was high or cranking speed slow, the starter motor is defective. More than .5 volt indicates excessive resistance. Isolate the trouble and correct the cause.

4. Check the neutral start switch or clutch switch for excessive voltage drop. Also check the ignition switch. Adjust or replace a defective switch, as necessary.

5. An alternate method to checking the voltage drop across each component is to leave the voltmeter connected to the battery (+) terminal and move the voltmeter negative lead back through the circuit toward the battery. The point of high resistance is found between the point where voltage drop fell within specs and the point last checked.



COMPONENT TESTS

For the various tests on starting system components, refer to the appropriate Toyota repair manual for testing procedures and specifications.

Ignition Switch and Key

The ignition switch should be checked both mechanically as well as electrically. Make sure the switch turns smoothly, without binding. And, check the ignition key for wear or metal chips that might cause the switch to stick in the "start" position. Some duplicate keys have caused this problem. If an electrical problem is suspected, disconnect the battery and check the switch for proper operation and continuity using an ohmmeter.

Starter Relay

• Continuity Check: Using an ohmmeter, check for continuity between terminals 1 and 3, and, for no continuity, between terminals 2 and 4. Replace the relay if continuity is not as specified.

• Operational Check: Apply battery voltage across terminals 1 and 3 and check for continuity between terminals 2 and 4. Replace the relay if operation is not as specified.

Neutral Start Switch

If the engine will start with the shift selector in any range other than "N" or "P," adjust the switch. First, loosen the switch bolt and set the selector to "N." Then, disconnect the switch connector and connect an ohmmeter between terminals 2 and 3. Adjust the switch until there is continuity. (Refer to appropriate Service Manual for specific vehicle procedures.)



Clutch Start Switch

Follow the procedure given in Toyota repair manuals for checking pedal height and freeplay. Then, check the switch for proper operation and continuity. Using an ohmmeter on the switch connector, there should be continuity when the switch is ON (clutch depressed) and no continuity when the switch is OFF (clutch not depressed). If continuity is not as specified, replace the switch.

Safety Cancel Switch

• Continuity Checks: Using an ohmmeter, there should be no continuity between terminals 2 and 1, 3 and 1, or 2 and 3. If there is continuity, replace the switch.

• Operational Checks: Connect a battery between terminals 3 and 1 as shown. No continuity should be seen between terminals 1 and 2. But, when the switch is pushed "on," there should be continuity. If operation is not as specified, replace the safety cancel switch.



SELF TESTThis brief self-test will help you measure your understanding of The Starting System. The style is the same as that used for A.S.E. certification tests.The answers to this self test are shown on next page.

1. The starting system has two circuits. They are the:

A. motor circuit and ignition circuitB. insulated circuit and power circuitC. motor circuit and control circuitD. ground circuit and control circuit

2. A basic starter control circuit energizes the magnetic switch through the ignition switch and the:

A. solenoidB. neutral start switchC. starter clutchD. regulator

3. On a Toyota gear-reduction starter, the plunger in the magnetic switch:

A. pulls a drive lever to mesh the gearsB. pushes the pinion gear into mesh with the

ring gearC. is held in place by the pull-in coilD. disengages the pinion gear from the starter

armature

4. When an engine starts, the pinion gear is disconnected from the starter by the:

A. magnetic switchB. plungerC. over-running clutchD. switch return spring

5. If the engine cranks too slow to start, the problem may be caused by:

A. engine problemsB. a faulty neutral start switchC. an open relay in the control circuitD. a damaged pinion gear

6. If a starter motor spins but does not engage and crank the engine, the problem is most likely caused by a bad:

A. magnetic switchB. over-running clutchC. positive battery cableD. ignition switch

7. When performing a starter current draw test, low current draw usually indicates:

A. high resistanceB. a bad starterC. a discharged batteryD. a short in the starter

8. When performing a starter current draw test, high current draw usually indicates:

A. a discharged batteryB. high resistanceC. battery terminal corrosionD. engine problems or a bad starter

9. A test of a starting system reveals that the voltage drop between the battery positive (+) post and the starter motor terminal "C" is about one volt. The most probable cause is:

A. low resistance in the motor circuitB. high resistance in the motor circuitC. low resistance in the control circuitD. high resistance in the control circuit

10. The voltage drop on the ground side of the starter motor circuit should be no more than:

A. battery voltageB. 0.1 voltC. 0.2 voltD. 0.5 volt



SELF-TEST ANSWERS

For the preceding self-test on The Starting System, the following best complete the sentence or answer the question. In cases where you may disagree with the choice - or may simply want to reinforce your understanding - please review the appropriate workbook page or pages noted.

1 . "C" - The starting system has two separate electrical circuits ... a control circuit and a motor circuit. (Page 1.)

2. "B" - If the transmission is in gear, the control circuit between the ignition switch and starter magnetic switch is interrupted by the neutral start switch. (Page 2.)

3. "B" - Unlike in the conventional starter, the magnetic switch plunger acts directly on the pinion gear (not through a drive lever) to push the gear into mesh with the ring gear. (Page 4.)

4. "C" - An over-running clutch disengages the pinion gear and prevents damage to the starter motor when the engine starts. (Page 7.)

5. "A" - If the engine cranks too slow to start, the cause may be a discharged battery, loose or corroded connections, a faulty starter, or engine problems such as the wrong oil. (Page 8.)

6. "B" - If the starter motor spins, but the engine will not crank, check the over-running clutch. (Page 8.)

7. "A" - Low current draw, with a low cranking speed and high cranking voltage, usually indicates excessive resistance in the starting circuit. (Page 10.)

8. "D" - High current draw, with a low cranking speed, usually indicates a faulty starter or engine problems such as the wrong oil or ignition timing. (Page 10.)

9. "B" - With the voltmeter leads connected between the battery (+) terminal and the motor "C" terminal, a reading of more than 0.5 volt indicates excessive resistance (in the motor circuit). (Page 11.)

10. "C" - With the voltmeter leads connected between the battery (-) terminal and the motor housing, a reading of more than 0.2 volt indicates excessive resistance (in the motor ground circuit). (Page 12.)




ASSIGNMENT NAME:

1. List the two staring system circuits.

2. List the components that make up the “control circuit”.

3. List the components that make up the “motor circuit”.

4. Explain in detail how a “Conventional Starter” differs from that of a “Gear Reduction Starter”.

5. Explain why an “overrunning clutch” is needed and how it works.

6. Explain how the “starter drive pinion” engages (pushed out) with the ring gear when the ignition key is turned to the “Start” position.

7. List and describe the five items included in a “Visual Inspection”.

8. Explain in detail the steps taken in order to perform a “Current Draw Test”.

9. Explain the procedure and the need for a voltage drop test of the “Motor Circuit”

General

The charging system converts mechanical energy into electrical energy when the engine is running. This energy is needed to operate the loads in the vehicle's electrical system. When the charging system's output is greater than that needed by the vehicle, it sends current into the battery to maintain the battery's state of charge. Proper diagnosis of charging system problems requires a thorough understanding of the system components and their operation.

Operation

When the engine is running, battery power energizes the charging system and engine power drives it. The charging system then generates electricity for the vehicle's electrical systems. At low speeds with some electrical loads "on" (e.g., lights and window defogger), some battery current may still be needed. But, at high speeds, the charging system supplies all the current needed by the vehicle. Once those needs are taken care of, the charging system then sends current into the battery to restore its charge.

CHARGING SYSTEMS


Toyota Charging Systems

Typical charging system components include:

IGNITION SWITCH When the ignition switch is in the ON position, battery current energizes the alternator.

ALTERNATORMechanical energy is transferred from the engine to the alternator by a grooved drive belt on a pulley arrangement. Through electromagnetic induction, the alternator changes this mechanical energy into electrical energy. The alternating current generated is converted into direct current by the rectifier, a set of diodes which allow current to pass in only one direction.

VOLTAGE REGULATOR Without a regulator, the alternator will always operate at its highest output. This may damage certain components and overcharge the battery. The regulator controls the alternator output to prevent overcharging or undercharging. On older models, this is a separate electromechanical component which uses a coil and contact points to open and close the circuit to the alternator. On most models today, this is a built-in electronic device.

BATTERYThe battery supplies current to energize the alternator. During charging, the battery changes electrical energy from the alternator into chemical energy. The battery's active materials are restored. The battery also acts as a "shock absorber" or voltage stabilizer in the system to prevent damage to sensitive components in the vehicle's electrical system.

INDICATORThe charging indicator device most commonly used on Toyotas is a simple ON/OFF warning lamp. It is normally off. It lights when the ignition is turned "on" for a check of the lamp circuit. And, it lights when the engine is running if the charging system is undercharging. A voltmeter is used on current Supra and Celica models to indicate system voltage ... it is connected in parallel with the battery. An ammeter in series with the battery was used on older Toyotas.

FUSINGA fusible link as well as separate fuses are used to protectcircuits in the charging system.

CHARGING SYSTEMS


Alternator Construction

GENERAL

Two different types of alternators are used on Toyota vehicles. A conventional alternator and separate voltage regulator were used on all Toyotas prior to 1979. A new compact, high-speed alternator with a built-in IC regulator

is now used on most models. Both types of alternators are rated according to current output. Typical ratings range from 40 amps to 80 amps.

CONVENTIONAL ALTERNATOR This type of alternator is currently used on some 1986 Tercel models, and all Toyotas prior to 1979.

CHARGING SYSTEMS


TOYOTA COMPACT, HIGH-SPEED ALTERNATOR

Beginning with the 1983 Camry, a compact, high-speed alternator with a built-in IC regulator is used on Toyota vehicles. Corolla models with the 4A-C engine use a different alternator with an integral IC regulator.

This new alternator is compact and lightweight. It provides better performance, as well as improved warning functions. If either the regulator sensor (terminal "S") or the alternator output (terminal "B") become disconnected, the warning lamp goes on. It also provides better serviceability. The rectifier, brush holder, and IC regulator are bolted onto the end frame.

CHARGING SYSTEMS


Alternator Terminals

Toyota's high-speed alternator has the following terminals: "B", "IG", "S", "U', and "17".

When the ignition switch is "on," battery current is supplied to the regulator through a wire connected between the switch and terminal "IG". When the alternator is charging, the charging current flows through a large wire connected between terminal "B" and the battery. At the same time, battery voltage is monitored for the MIC regulator through terminal "S". The regulator will increase or decrease rotor field strength as needed. The indicator lamp circuit is connected through terminal "U'. If there is no output, the lamp will be lit. The rotor field coil is connected to terminal "P, which is accessible for testing purposes through a hole in the alternator end frame.

Regulator

While engine speeds and electrical loads change, the alternator's output must remain even - not too much, nor too little.

The regulator controls alternator output by increasing or decreasing the strength of the rotor's magnetic field. It does so, by controlling the amount of current from the battery to the rotor's field coil.

The electromechanical regulator does its job with a magnetic coil and set of contact points. The IC regulator does its job with diodes, transistors, and other electronic components.

CHARGING SYSTEMS


Alternator Operation

GENERAL

The operation of the Toyota compact, high-speed alternator is shown in the following circuit diagrams.

IGNITION ON, ENGINE STOPPED

CHARGING SYSTEMS


CHARGING SYSTEMS



The charging system requires periodic inspection and service. Specific problem symptoms, their possible cause, and the service required are listed in the chart below. The service actions require a thorough visual inspection. Problems identified must be corrected before proceeding with electrical tests. These electrical tests include: an alternator output test, charging circuit voltage-drop tests, a voltage regulator (non-IC) test, charging circuit relay (lamp, ignition, engine) tests, and alternator bench tests.

PRECAUTIONS• Make sure battery cables are connected to correct terminals.

• Always disconnect battery cables (negative first!) when the battery is given a quick charge.

• Never operate an alternator on an open circuit (battery cables disconnected).

• Always follow specs for engine speed when grounding terminal "F to bypass the regulator. High speeds may cause excess output that could damage components.

• Never ground alternator output terminal "B." It has battery voltage present at all times, even with the engine off.

• Do not perform continuity tests with a high- voltage insulation resistance tester. This type of ohmmeter could damage the alternator diodes.

CHARGING SYSTEMS


VISUAL INSPECTIONA visual inspection should always be your first step in checking the charging system. A number of problems that would reduce charging performance can be identified and corrected.

CHECK THE BATTERY• Check for proper electrolyte level and state of

charge. When fully charged, specific gravity should be between 1.25 and 1.27 at 80˚F (26.7˚C).

• Check the battery terminals and cables. The terminals should be free of corrosion and the cable connections tight.

CHECK THE FUSES AND FUSIBLE LINK• Check the fuses for continuity. These include the

Engine fuse (10A), Charge fuse (7.5A), and Ignition fuse (7.5A).

• Check the fusible link for continuity.

INSPECT THE DRIVE BELT• Check for belt separation, cracks, fraying, or

glazing. If necessary, replace the drive belt.

• Check the drive belt tension using the proper tension gauge, Nippondenso BTG-20

Refer to the appropriate repair manual for proper drive belt tension. "New" belts (used less than 5 minutes on a running engine) are installed with greater tension than "used" belts. Tension specs are different for different models.

INSPECT THE ALTERNATOR• Check the wiring and connections. Replace any

damaged wires, tighten any loose connections.

• Check for abnormal noises. Squealing may indicate drive belt or bearing problems. Defective diodes can produce a whine or hissing noise because of a pulsating magnetic field and vibration.

CHECK THE WARNING LAMP CIRCUIT• With the engine warm and all accessories off, turn the ignition to ON. The warning lamp should light.

• With the engine started and the ignition in RUN, the warning lamp should be off.

• If the lamp does not operate as specified, check the bulb and check the lamp circuit.

CHARGING SYSTEMS


ALTERNATOR OUTPUT TEST

The alternator output test checks the ability of the alternator to deliver its rated output of voltage and current. This test should be performed whenever an overcharging or undercharging problem is suspected. Output current and voltage should meet the specifications of the alternator. If not, the alternator or regulator (IC or external) may require replacement.

A Sun VAT-40 tester, similar testers, or a separate voltmeter and ammeter can be used. Toyota repair manuals detail the testing procedures with an ammeter and voltmeter. Follow the manufacturer's instructions when using special testers, although most are operated similarly. The following steps outline a typical procedure for performing the alternator output test using a Sun VAT-40:

CHARGING SYSTEMS


Charging Without Load1. Prepare the tester:

• Rotate the Load Increase control to OFF,

• Check each meter's mechanical zero. Adjust, if necessary.

• Connect the tester Load Leads to the battery terminals; RED to positive, BLACK to negative.

• Set Volt Selector to INT 18V.

• Set Test Selector to #2 CHARGING.

• Adjust ammeter to read ZERO using the electrical Zero Adjust control.

• Connect the clamp-on Amps Pickup around the battery ground (-) cables.

2. Turn the ignition switch to "ON" (engine not running) and read the amount of discharge on the ammeter. This is a base reading for current the alternator must supply for ignition and accessories before it can provide current to charge the battery.

NOTE: The reading should be about six amps.

3. Start the engine and adjust the speed to about 2000 rpm. Some models may require a different speed setting.

4. After about 3-4 minutes, read the ammeter and

voltmeter. Add this ammeter reading and the reading found in step 2 (engine not running).

NOTE: The total current should be less than 10 amps. If it is more, the alternator may still be charging the battery. Once the battery is fully charged, you should get specified results.

The voltage should be within the specs for the alternator. This is usually between 13 and 15 volts. Refer to the appropriate repair manual. If the voltage is more than specified, replace the regulator. If the voltage is less than specified, ground the alternator field terminal "F" and check the voltmeter reading. This bypasses the regulator, so do not exceed the specified test speed. If the reading is still less than specified, check the alternator.

5. Remove ground from terminal "F."

Charging With Load6. With the engine running at specified speed,

adjust the Load Increase control to obtain the highest ammeter reading possible without causing the voltage to drop lower than 12 volts.

7. Read the ammeter.

NOTE: The reading should be within 10% of the alternator's rated output. If it is less, the alternator requires further testing or replacement.

CHARGING SYSTEMS


CHARGING SYSTEMS


VOLTAGE-DROP TESTSVoltage-drop testing can detect excessive resistance in the charging system. These tests determine the voltage drop in the alternator output circuit. Both sides of the circuit should be checked ... insulated side as well as ground side. Excessive voltage drop caused by high resistance in either of these circuits will reduce the available charging current. Under heavy electrical loads, the battery will discharge.

A Sun VAT-40 tester or a separate voltmeter can be used. The following steps outline a typical procedure for performing voltage-drop tests using a voltmeter:

Output Circuit - Insulated Side

1. Connect the voltmeter positive lead to the alternator's output terminal "B" and the voltmeter's negative lead to the battery's positive (+) terminal.

2. Start the engine and adjust the speed to approximately 2000 rpm.

3. Read the voltmeter. The voltage drop should be less than 0.2 volt. If it is more, locate and correct the cause of the high resistance.

Output Circuit - Ground Side

1. Connect the voltmeter's negative lead to the alternator's frame and the voltmeter's positive lead to the battery's negative (-) terminal.

2. Start the engine and run at specified speed (about 2000 rpm).

3. Read the voltmeter. The voltage drop should be 0.2 volt or less. If it is more, locate and correct the cause of high resistance. Excessive resistance is most likely caused by loose or corroded connections.

CHARGING SYSTEMS


CHARGING CIRCUIT RELAY TESTS

Various charging system layouts are used on Toyota vehicles. The indicator lamp circuit may or may not be controlled by a relay. Depending on the model, when a relay is used, it may be a separate lamp relay, the ignition main relay, or the engine main relay. Each is checked using an ohmmeter.

Charge Lamp Relay

When used, the charge lamp relay is located on the right cowl side of the vehicle. The following steps are used to check this relay:

1. Check relay continuity.

• Connect the ohmmeter positive (+) lead to terminal "4," the negative (-) lead to terminal "3." Continuity (no resistance) should be indicated.

• Reverse the polarity of the ohmmeter leads. No continuity (infinite resistance) should be indicated.

• Connect the ohmmeter leads between terminals 1 and "2." No continuity (infinite resistance) should be indicated.

If the relay continuity is not as specified, replace the relay.

2. Check relay operation.

• Apply battery voltage across terminals "3" and "4."

NOTE: Make sure polarity is as shown.

• Connect the ohmmeter leads between terminals “1” and "2." Continuity (no resistance) should be indicated.

If relay operation is not as specified, replace the relay.

CHARGING SYSTEMS


Ignition Main Relay

The ignition main relay is located in the relay box under the instrument panel. The following steps are used to check this relay:

1. Check relay continuity.

• Connect the ohmmeter leads between terminals “1” and "3." Continuity (no resistance) should be indicated.

• Connect the ohmmeter leads between terminals "2" and "4." No continuity (infinite resistance) should be indicated.

If relay continuity is not as specified, replace the relay.

2. Check relay operation.

• Apply battery voltage across terminals "l " and "3."

• Connect the ohmmeter leads between terminals "2" and 'A." Continuity (no resistance) should be indicated.

If relay operation is not as specified, replace the relay.

CHARGING SYSTEMS


ALTERNATOR BENCH TESTS

If the on-vehicle checks have indicated that the alternator is defective, it should be removed for bench testing and replacement. Specific procedures for removal, disassembly, inspection, and assembly are noted in the appropriate repair manuals. Only the electrical bench tests are covered here.

• Always disconnect the battery ground (-) cable before removing the alternator.

• Refer to the appropriate repair manual for test specifications.

An ohmmeter is used for electrical bench tests on the rotor, stator, and diode rectifier. The following steps are typical:

Rotor Tests

• Check the rotor for an open circuit by measuring for resistance between the slip rings. Some resistance (less than 5 ohms) indicates continuity. If there is no continuity (infinite resistance), replace the rotor.

• Check the rotor for grounded circuits by measuring for resistance between the rotor and

slip ring. Any amount of resistance indicates a ground (continuity). The resistance should be infinite ( 0 ohms ). If not, replace the rotor.

CHARGING SYSTEMS


Diode Tests

Diodes can be checked with the alternator on the vehicle using a scope. Scope testing can identify open or shorted diodes, as well as problems in the stator coils. The scope patterns shown below include:

a) Normal alternator output;

b) one diode short-circuited;

c) two diodes of the same polarity short-circuited;

d) one diode open;

e) two diodes open;

f) one phase of the stator coil short-circuited;

g) one phase of the stator coil disconnected; and,

h) two phases of the stator coil short-circuited.

CHARGING SYSTEMS


CHARGING SYSTEMS


This brief self-test will help you measure your understanding of The Charging System. The style is the same as that used for A.S.E. certification tests. Each incomplete statement or question is followed by four suggested completions or answers. In each case, select the one that best completes the sentence or answers the question.

1. A regulator controls alternator output voltage by regulating:

A. sine-wave voltageB. battery voltageC. field currentD. output current

2. In an alternator, alternating current is converted to direct current by the:

A. statorB. brushesC. rectifierD. regulator

3. If the charging system indicator lamp goes on with the engine running, the cause may be loss of voltage at terminal:

A. "IG"B. "S"C. "L"D. "F

4. With the engine not running and the ignition ON, the charge lamp should light. If it doesn't, this may indicate a:

A. burned out bulbB. grounded bulbC. loose drive beltD. overcharged battery

5. Which alternator terminal can be grounded for test purposes?

A. "B" B. "IG"C. “S"D. "F

6. When performing a visual inspection of the charging system, the alternator drive belt should be checked for proper tension.

Technician "A" says that new-belt tension specs are higher than those for used belts.

Technician "B" says that the belt tension is different for different Toyota models.

Who is right?

A. Only AB. Only BC. Both A and BD. Neither A nor B

7. The amount of current the alternator must supply or ignition and accessories is about:

A. four ampsB. six ampsC. eight ampsD. ten amps

8. In an alternator output test under load, the output should be:

A. about 10 ampsB. about 30 ampsC. within 10% of rated outputD. within 20% of rated output

9. To check for excessive voltage drop on the insulated side of the alternator's output circuit, you would connect a voltmeter between the:

A. battery terminal and ignition switchB. battery terminal and groundC. battery terminal and alternator "S" terminalD. battery terminal and alternator "B" terminal

10. High resistance in an alternator output circuit is often caused by:

A. a discharged batteryB. a shorted diodeC. loose or corroded connectionsD. a bad regulator

CHARGING SYSTEMS


SELF-TEST ANSWERS

For the preceding self-test on The Charging System, the following best complete the sentence or answer the question. In cases where you may disagree with the choice - or may simply want to reinforce your understanding - please review the appropriate workbook page or pages noted.

1 . "C" - The regulator controls alternator output by increasing or decreasing the amount of current from the battery to the rotor field coil. (Page 5.)

2. "C" - The alternating current is changed into direct current by the rectifier, a set of diodes which allow current to pass in only one direction. (Page 2.)

3. "B" - If either the regulator sensor (terminal "S") or the alternator output (terminal "B") become disconnected, the warning lamp goes on. (Page 4.)

4. "A" - If the warning lamp does not light, with the ignition ON and the engine not running, the possible causes include a blown fuse, burned out lamp, loose connections, or faulty relay or regulator. (Page 9.)

5. "D" - Terminal "F is the only terminal that can be grounded. Never ground alternator output terminal "B. It has battery voltage present at all times, even with the engine off. (Page 9.)

6. "C" - A "new belt" is one that has been used for less than 5 minutes. It is installed with more tension than a used belt, because it will stretch some during use. Methods of checking are different for different models. (Page 10.)

7. "B" -The reading should be about six amps. This is the amount of current the alternator must supply for ignition and accessories. (Page 12.)

8. "C" - With the alternator operating at maximum output, the reading should be within 10% of rated output. (Page 12.)

9. "ID" - To check for the insulated circuit voltage drop, connect the voltmeter leads to the battery's (+) terminal and the alternator output (B) terminal. (Page 14.)

10. "C" - Excessive resistance is most likely caused by loose or corroded connections. (Page 14.)

CHARGING SYSTEMS


Kevin R. Sullivan

Kevin R. Sullivan

Taken with permission from the Toyota Basic Electrical Course#622,

USING THE ELECTRICAL WIRING DIAGRAM

USING TOYOTA WIRING DIAGRAMS


ELECTRICAL DIAGNOSTIC TOOLS

Page 1 ' Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.

DIAGNOSING BODY ELECTRICAL PROBLEMS


SEMICONDUCTORS

One of the basic building blocks of allmodern electronic devices is thesemiconductor. Semiconductors canconduct or block electrical current.Because of this ability, semiconductorsserve an important function in everythingfrom relays to the integrated circuits ofcomputers.

This chapter examines diodes as well assome of the other components used toconstruct electronic devices, such ascapacitors and resistors. Diodes allowcurrent to flow through them in only onedirection and are used in a variety ofways, including suppression of voltagespikes ("de-spiking") and convertingalternating current to direct current inan alternator.

Capacitors store electrical charges andare used for electrical noise and voltagespike suppression. Capacitors are alsoused in timer circuits to delay turning onor off a device or system.

This chapter will examine each of thefollowing areas:

CapacitorsCurrent Flow TheorySemiconductor TheoryDiodes

CAPACITORS

Capacitors have the ability to absorb andstore an electrical charge and thenrelease it into the circuit. Capacitors arefrequently used in timers which will keepa circuit or device in operation for aperiod of time after the circuit has beenshut off. An example of this is a domelight circuit that stays on for a specifiedlength of time after the door has beenclosed.

A capacitor is constructed from twoconducting plates separated by aninsulating material called a dielectric.This insulating material can be paper,plastic, film mica, glass, ceramic, air ora vacuum. The plates can be aluminumdiscs, aluminum foil or a thin film ofmetal applied to opposite sides of a soliddielectric. These layered materials areeither rolled into a cylinder or left flat.

The operation of a capacitor is relativelysimple. When the capacitor is placed in acircuit, a charge builds on the plates untilthe plates are at the same potential as thepower source. When the source potentialis removed, the capacitor will dischargeand cause a current to flow in the circuit.If the potential of the source changes, thecapacitor will either charge or dischargeto match the source, thereby smoothingvoltage fluctuations in the circuit.

SEMICONDUCTORS


Since current can flow into a capacitoronly until the charge reaches thepotential of the source, a capacitor willblock current in a DC circuit. ACcurrents are not blocked by a capacitorbecause the polarity of the AC circuit iscontinually changing.

The unit of measure of capacitance is the"farad." Most capacitors are much lessthan one farad, and are rated in micro-farads or picofarads. When capacitorsare connected in series their totalcapacitance is reduced, like resistorsconnected in parallel. When capacitorsare connected in parallel their totalcapacitance increases, like totalresistance when resistors are connected in series.

There are three types of capacitors:ceramic for electronic circuits, paper andfoil for noise suppression in charging andignition systems, and electrolytic as usedin turn signal flashers. Ordinary andelectrolytic capacitors are designated bydifferent symbols in wiring diagrams.

As stated, capacitors have three uses:

Noise suppression—Noise in an audiosystem is often caused by AC electricalvoltage riding on top of the DC voltagesupplying power to a radio or tape player.A capacitor connected to the circuit willfilter out the AC voltage by allowing it topass to ground. Most alternators onToyota vehicles have a capacitor built infor this purpose.

Spike suppression—A capacitor canabsorb voltage spikes in a circuit. Thisapplication has been used in conventionalignition systems to prevent an arc fromjumping the breaker points when theyare opened.

Timers—A resistor put in series with acapacitor can keep current flowing in acircuit for a specified amount of timeafter power from the source has beenremoved. This can be used to keep domelights on after the vehicle doors areclosed. The resistor-capacitor or RCcircuit in the example above is used tokeep a transistor turned on, so thetransistor allows current to remainflowing to the system.

SEMICONDUCTORS


CURRENT FLOW THEORY

Before we discuss semiconductors andhow they operate, it is important tounderstand current flow theory. Thereare two different theories of how currentflows: electron current flow andconventional current flow (sometimesreferred to as "hole flow").

The electron current flow theory says thatcurrent flow in a circuit is the movementof electrons through the conductors.Since the electrons have a negativecharge and unlike charges attract eachother, the electrons move from thenegative terminal of the battery to thepositive terminal. So the electron theorysays that current flows from negative topositive.

The conventional current flow theory,which has been accepted for many years,says that current flows from the positiveterminal of the battery to the negativeterminal. The conventional current flowtheory is sometimes called the hole flowtheory because this theory says that whenan electron moves, an empty hole is left

behind. The holes are said to travel in theopposite direction from the electrons inthe conductor. To understand how thiscould work think of a line of cars stoppedat a stop sign. As one car pulls away fromthe stop sign a hole is left and the next carin line moves forward to fill the hole. Nowthe hole has moved back to where thesecond car was and the third car movesforward to fill it. As each car in turnmoves forward to fill the hole, the holemoves to the rear. The cars move onedirection and the holes move the other,just like electrons and holes in a circuit.

When looking at an electrical circuit,either the electron current flow theory orconventional current flow theory can beapplied because the circuit operation andthe schematic will be the same. Whendealing with diagrams that use electronicsymbols, such as diodes and transistors,the arrow in the symbol always points inthe direction of conventional current flow.Because the conventional current flowtheory is widely accepted in theautomotive industry, it is usedthroughout this book.

SEMICONDUCTORS


BASIC THEORY OFSEMICONDUCTOR OPERATION

Semiconductors are important tounderstand because they play such aprominent part in automotive electronics.You will deal with them nearly everytime you diagnose a Toyota electronicsystem.

Some materials conduct electricalcurrent better than others. This is due tothe number of electrons in the outermostring, or shell, of electrons of the atomsthat make up the materials. The outershell is called the valence shell" or"ring." If the valence ring has five toeight electrons, it takes a large amount offorce to cause one of the electrons to breakfree from the atom, making that materiala poor conductor. Such materials areoften used as insulators to block current.materials that are made up of atoms withone to three electrons in their valencering are good conductors because a smallforce will cause the electrons to breakfree. Semiconductors fall somewhere inthe middle. Since they have four electronsin their valence rings, they are not goodinsulators or conductors.

Semiconductors are usually made fromgermanium or silicon which, in theirnatural states, are pure crystals. Neitherhave enough free electrons to supportsignificant current flow, but by addingatoms from other materials—a processcalled doping— the crystals will conductelectricity in a way that is useful inelectronic circuits. The semiconductormaterial, after it has been doped, becomeseither N-type material or P-type material.

SEMICONDUCTORS


Silicon is the most commonly usedsemiconductor material. The outer shellof a silicon atom contains four electrons,but it needs eight to be stable. Therefore,the atoms link together to shareelectrons. In this state, silicon will notconduct current.

When silicon is doped with a materialsuch as phosphorous, which has fiveelectrons, the resultant material containsfree electrons—known as carriers—andtherefore conducts electricity. Thiscreates N-type material, named for itsnegative charge caused by the excess ofelectrons.

Silicon can also be doped with a materialthat has fewer than four electrons in itsouter shells, as is the case with boron andits three electrons. The resultantstructure has "holes" left by the missingelectrons. As discussed earlier, anelectron can move into these holes and, ineffect, the hole moves in the oppositedirection. The abundance of holes createsP-type material, named for its positivecharge due the lack of electrons or excessof holes. By joining this N-type and P-typematerial, diodes and transistors can beformed.

DIODES

Diodes block current flow in one directionand pass current in the oppositedirection. This is accomplished by joininga layer of P type material and a layer of N-type material during manufacturing.Where they meet is called the PNjunction. At the PN junction, some of theelectrons of the N-type material move intosome of the holes in the P-type materialand create a neutral area at the junction.Another way of thinking of this is that thepositive holes attract the negativeelectrons leaving no free electrons, socurrent is unable to flow past that point.This neutral area acts as a barrier,which is called the depletion region.

SEMICONDUCTORS


The depletion region is very thin andresponds rapidly to voltage changes. It ishere that current is either allowed to passor is blocked.

When the diode is connected in a circuitwhere the N-type material is connected tothe negative terminal of the battery andthe P-type material is connected to thepositive terminal, the excess electrons inthe N-type material are repelled by thenegative potential of the battery. At thesame time, the positively charged holes inthe P-type material are repelled by thepositive potential of the battery, resultingin a concentration of holes and electronsat the depletion region. When voltageapplied to the diode is great enough (.5 to.7 volts) electrons in the N type materialwill move across the depletion

region at the junction, filling holes in theP-type material and leaving holes in theN-type material. Electrons move throughthe diode to the positive terminal of thebattery and holes move through the diodeto the negative terminal of the battery.When this happens the diode conductscurrent and is said to be forward biased.

If the connection of the diode in thecircuit is reversed, with the N-typematerial connected to the positiveterminal of the battery and the P-typematerial connected to the negativeterminal, the diode is reverse

biased. In this case, the electrons in theN-type material are attracted to thepositive terminal of the battery and theholes in the P-type material are attractedto the negative terminal of the battery.This results in an increase in thedepletion region or neutral zone so nocurrent can flow through the diode.Whether the diode conducts or blockscurrent flow is determined by the voltagepolarity applied to it.

SEMICONDUCTORS


If the reverse bias voltage applied to adiode is great enough, the voltage canovercome the depletion region at thejunction and the diode will conduct for ashort period before burning open. Whenthis happens the diode is destroyed.

The three main uses for diodes in theautomobile are rectification, de-spiking,and isolation.

Rectification—Since a diode will allowcurrent to flow in one direction and notthe other, it can be used to turnalternating current into direct current.This is called rectification. Diodes canprovide either full-wave or half-waverectification, depending on the number ofdiodes and how they are connected.

A half-wave rectifier consisting of onediode will have an output voltage that isapproximately one half of the AC source.Since the output from an AC powersource continually changes or alternatesfrom positive to negative, the diode isforward biased for part of the output andreverse biased for the other. The diodewill allow current to flow in the circuitwhen it is forward biased but will blockthe flow of current when it is reverse

biased. The result is that only half of thewave is output while the other half isblocked by the diode. This type of rectifieris not commonly found in an automotiveapplication since it is not an efficient wayto rectify AC to DC to charge a battery.

A full-wave rectifier uses a four-diodenetwork to rectify both halves of an ACoutput. In such a system, current flowsfrom the first half of the phase of the ACpower source through the first diode inforward bias, through the externalcircuit, through the second diode, thencompletes the circuit. On the second halfof the phase, the current flows throughthe third diode, through the externalcircuit, through the fourth diode andcompletes the circuit.

SEMICONDUCTORS


By using four diodes in the full-waverectifier, all of the current flows to the DCpart of the circuit and the current in theDC part always flows the same directioneven though the current flow in the ACpower source changes directions.

The full-wave, three-phase rectifier foundin an automotive alternator goes a stepfurther. Because the alternator usesthree coils that produce three overlappingAC sine waves staggered at 120 degreeintervals, six diodes are required toachieve full-wave rectification. Each coiluses four of the diodes to rectify theoutput, achieving full-wave rectification(as in the full-wave, single-phase rectifierdiscussed earlier). Because the coils anddiodes are interconnected, the samediodes are used by different coils atdifferent times. Due to the overlap of thewaves, output from each coil in this typeof alternator produces a smooth output tothe DC system.

The following worksheet shows how thesix diodes can rectify the output of allthree coils.

SEMICONDUCTORS


DIODE RECTIFICATION WORKSHEET

In each of the illustrations above, tracethe path of current flow through thestator coils, the corresponding diodes andthe DC circuit.

The arrows in the illustrations next to thestator coils show the direction ofconventional current flow.

SEMICONDUCTORS


De-spiking—Diodes are used on somerelay coils to suppress voltage spikes.These spikes can damage componentssuch as transistors in the control circuitof the relay. The voltage spike is producedby the collapsing magnetic field in therelay coil which occurs whenever currentflow through the coil is stopped suddenly.The voltage induced in the relay coil issimilar to the way an ignition coiloperates. The induced voltage in a relaycoil can be several times more than thesystem voltage.

A de-spiking diode is connected inparallel with the relay coil. It is reversebiased when the relay is turned on,therefore no current

will flow through the diode. When therelay control circuit is opened, currentstops flowing through the coil, causingthe magnetic field to collapse. Themagnetic lines of force cut through thecoil and induce a voltage. Since thecircuit is open, no current flows. Thevoltage builds until it reaches about .7volts, enough to forward bias the diode,completing the circuit to the other end ofthe coil. The current flows around in thediode and coil circuit until the voltage isdissipated.

Because some relays are located in veryhot environments where de-spikingdiodes can fail prematurely, resistors aresometimes used instead. The resistor ismore durable and can suppress voltagespikes in much the same way as thediode, but the resistor will allow currentto flow through it whenever the relay ison. Therefore resistance of the resistormust be fairly high (400 to 600 ohms) toprevent too much current flow in thecircuit. Because of resistors' highresistance, they are not quite as efficientat suppressing a voltage spike as diodes.

SEMICONDUCTORS


Isolation—A diode can be used toseparate two circuits. Diodes are used inthis way on many Toyota models. TheElectronic Load Sense (ELS) circuit usedon a Camry is a good example. Thissystem signals the ECU to increase theidle speed when certain electrical loadsare turned on. It uses two diodes so twodifferent circuits can provide a voltagesignal to the same terminal on the ECU.Without diodes, whenever either of thesystems were turned on, voltage wouldalso be applied to the other circuitcausing it to operate.

SEMICONDUCTORS


Zener diode—A zener diode acts like anordinary silicon diode when in theforward bias direction, but it has beenspecially doped to act very differently inreverse bias. A zener diode allowscurrent to flow in reverse bias at aspecific voltage without damage over andover again. The reverse bias voltage atwhich the zener will conduct, sometimescalled the zener point, differs from onezener to another as each zener diode isdoped to have a zener point at a specificvoltage.

A zener diode can be used to suppressspikes by connecting it between the circuitand ground with the diode reverse biased.When a voltage spike exceeds the zenerpoint of the diode, it completes the circuitto ground and prevents the spike fromdamaging anything.

A more common use of a zener diode inan automobile is to sense the chargingsystem voltage. By connecting the zenerbetween the base of a transistor and thepositive side of the charging system, thezener can allow current to flow to the baseof the transistor when its zener point isreached. If the zener point is 14.5 voltsand the transistor to which the zener isconnected turns off alternator fieldcurrent when the transistor is turned on,a constant charging system voltage canbe maintained. As soon as the systemvoltage drops below the zener point, thediode stops conducting and the transistorturns off, allowing field current to flow.

SEMICONDUCTORS


Light emitting diodes (LEDs)—An LED isa diode that is specially designed toproduce light. LEDs are made with atransparent epoxy case so they can emitthe light they produce when forwardbiased. The color of the light given off byan LED can be red, green or infrared,depending on how the material is dopedAn LED, like a standard silicon diode,will conduct current in only onedirection. The forward bias voltage dropof an LED (1.5 to 2 volts) is much higherthan a silicon diode. The forward biascurrent through an LED must becontrolled, as with any othersemiconductor' or damage will result.LEDs have advantages over ordinarybulbs, such as longer life, cooleroperation, lower voltage requirementsand the ability to produce the sameamount of light as an incandescent bulbwhile consuming less power.

In vehicles, LEDs are used in a variety ofways, including displays and indicators.LEDs are also used in conjunction withphototransistors, which convert light toelectrical current. A vehicle speedsensor, known as a photo-coupler orlight-activated switch, is a good example.In a speed sensor, the speedometer cableis connected to a slotted wheel whichseparates the LED from thephototransistor. As the wheel turns, itconstantly breaks the beam of lightemitted from the LED to thephototransistor, thereby turning thephototransistor on and off. The pulsedsignal goes to the computer and is used todetermine vehicle speed.

Taken with permission from the Toyota,Advanced Electrical Course#672

SEMICONDUCTORS


SEMICONDUCTORS

ASSIGNMENT NAME:

1. Describe the construction and operation of a capacitor.

2. Name the three types of capacitors.

3. Describe the three uses of capacitors.

4. Name and explain both current flow theories.

5. Describe how a semicondor differs from a conductor or an insulator.

6. What are two common types of semiconductor material.

7. Explain what “Doping “ is and how N-Type or P-Type material is made.

8. Describe the function and construction of a “Diode”.

9. Explain the term PN junction.

10. Describe the depletion region of a diode.

11. What is the voltage drop (the voltmeter reading) of a diode?

12. Explain the terms “Forward” and “Reverse” Bias.

13. Describe Rectification and how diodes are used.

14. Explain the difference between half-wave and full-wave rectification.

15. Describe the function of a De-spiking (Voltage Suppression) diode.

16. Explain the operation of a De-spiking (Voltage Suppression) diode.

17. Describe the function of an Isolation diode.

18. Explain the operation of an Isolation diode.

19. Explain how a “Zener Diode” differs from a conventional diode.

20. Explain the term “Zener Point” (Avalanche Point) and what happens at this point.

21. Explain how a “Light Emitting Diode” (LED) differs from a conventional diode.

22. What is the voltage drop (the voltmeter reading) of an LED?

THE BIPOLAR TRANSISTOR

TRANSISTORS

A transistor can be used as an amplifierto control electric motor speed such as ACblower motors, or as solid state switchesto control actuators such as fuel injectors.

This chapter will cover each of thefollowing four areas:

Transistor Operation

Transistor Applications

Transistor Gain

Integrated Circuits

Transistors are made from the same N-type and P-type materials as diodes andemploy the same principles. Transistors,however, have two PN junctions insteadof just one like a diode has. The two PNjunctions allowa transistor to perform more functionsthana diode, such as acting as a switch or anamplifier.

The bipolar transistor is made up of threeparts: the emitter, the base and thecollector. There are two types of bipolartransistors: the PNP and the NPN. In thePNP transistor the emitter is made fromP-type material, the base is N-typematerial and the collector is P-typematerial. For the PN transistor tooperate, the emitter must be connected topositive, the base to negative and thecollector to negative.

The NPN transistor has an emitter madefrom N-type material. Its base is P-typematerial and the collector is N-typematerial. For the NPN transistor tooperate, the emitter must be connected tonegative, the base to positive and thecollector to positive Aside from the way inwhich the NPN and PNP transistors areconnected in the circa they operate thesame way. Both transistor have a forwardbiased junction and a reverse biasedjunction, and three parts-the emitter, thebase and the collector-formed in a three-layer arrangement

TRANSISTORS


Current flow between the emitter andbase controls the current flow between theemitter and collector. The emitter of thetransistor is the most heavily doped so ithas the most excess electrons or holes,depending on whether the emitter is P-type or N-type material. The collector isdoped slightly less than the emitter andthe base is very thin with the fewestdoping atoms. As a result of this type ofdoping, the current flow in the emitter-collector is much greater than in theemitter-base. By regulating the current atthe emitter-base junction, the amount ofcurrent allowed to pass from the emitterto the collector can be controlled.

The symbols for both PNP and NPNtransistors are very similar. Thedistinguishing feature is the arrow,which is always located in the emitterand always points in the direction ofconventional current flow. The base ispart of the symbol which looks like a "T"and the remaining line, opposite theemitter, is the collector. In the symbol fora PNP transistor the arrow in the emitterpoints toward the center so the currentflow is from emitter to base and fromemitter to collector. In the NPN transistorthe arrow

in the emitter points away from thecenter so the current flow is from the baseto emitter and from the collector toemitter.

One of the most common uses of atransistor in an automobile is as aswitch. Switching transistors can befound in solid state control modules andcomputers. They control devices on thecar such as the fuel injector in an EFI caror a mechanical relay that operates theretract motor on a car with retractableheadlights. When an NPN transistor isused as a switch, the emitter of thetransistor is grounded and the base isconnected to positive. If the voltage isremoved from the base, no current flowsfrom the emitter to the collector and thetransistor is off. When the base is forwardbiased by a large enough voltage, currentwill flow from the emitter to the collector.Essentially, the transistor is being used tocontrol a large current with a smallcurrent like a starter relay. A smallamount of current to the relay willcomplete a circuit so a large current canflow.

TRANSISTORS


TRANSISTOR GAIN

We know that the current flow betweenthe emitter and base controls the currentflow between the emitter and collector.Also, the amount of current flow betweenthe emitter and base will affect theamount of emitter collector current. Theratio between these two currents isknown as the "gain" of the transistor.This gain allows us to use a transistor tocontrol a large current with a very smallcurrent similar to the way a relayoperates. Example shown: if a transistorhad a gain of 100 and the emitter-basecurrent was increased by 10 milliamps or.01 amps, the emitter collector currentwould increase by 100 times or 1 amp.This type of increase will occur until thetransistor reached saturation. This is thepoint where increasing the emitter-basecurrent does not increase the emitter-collector current. Transistors used forswitching usually operate at thesaturation point when turned on, whiletransistors that are used for amplifiersoperate in the range between off andsaturation.

Another application for a transistor isamplification. This situation takesadvantage of the relationship between theemitter base current and the emitter-collector current. Since a small change incurrent flowing through the transistorfrom the emitter to the base has aproportionally larger effect on theemitter-collector current, we can usetransistors to increase the strength of asmall signal in a radio or to provide avariable control for a motor.

On some Toyota models, transistors arebeing used to provide variable speedcontrol such as the AC blower motor onthe Cressida and the electric motor thatruns the power steering pump on the 1991MR2. By varying the emitter-base currentof the transistor, the current flowingthrough the motor can be varied, therebyvarying the motor speed.

TRANSISTORS


INTEGRATED CIRCUITS

An integrated circuit (IC) is nothingmore than many transistors, diodes,capacitors and resistors connectedtogether with conductors and placed on asingle silicon chip. A single IC is asystem within a system, with several toseveral thousand electrical circuits builtinto or onto a several-squaremillimetersilicon chip in a ceramic or plasticpackage. The advantages of the IC are thesize and low cost of mass productionalong with low power consumption andreliability. An IC can be anything fromsimple logic gate to a microprocessor toalmost a complete computer on a chip.

ICs are more reliable than non-integrated circuits because all theelements can be built into and onto asingle silicon chip, thereby reducingcontact junctions. In addition, thenumber of components is reduced.

ICs are classified by the number of partsincluded on one chip. The Small ScaleIntegration (SSI) IC has about 100elements; the Medium Scale Integration(MSI) IC has 100 to 1,000 elements; theLarge Scale Integration (LSI) IC has10,000 to 100,000 elements; and the VeryLarge Scale Integration (VLSI) IC hasmore than 100,000 elements.

Taken with permission from the ToyotaAdvanced Electrical Course#672

TRANSISTORS


TRANSISTORS

ASSIGNMENT NAME:

1. Describe the basic construction of a Bipolar Transistor.

2. Draw a PNP Transistor and label its parts.

3 Explain the two current paths of a bipolar transistor.

4. Explain the purpose of the arrow on the emitter and why is the direction of it important.

5. If the arrow on the emitter is pointing toward the base. What type of transistor is it and what voltage signal (positive or negative) is needed to the base in order to forward bias the transistor?

6. Explain and provide an example of “transistor gain”.

7. Describe what an integrated circuit is.

COMPUTERS AND LOGIC CIRCUITS

Dealing with computers can seemoverwhelming for those who areaccustomed to working with mechanicalsystems. Since we cannot actually seewhat is going on inside the computer orthe system it controls, computers may notbe as easy to understand as mechanicalcomponents such as transmissions andengines. However, computers are not ascomplicated as they might sound. Thischapter will help demystify computers.

The computers found on a vehicle arereally no different than any othercomputer encountered in everyday life.Vehicle computers rely on data fromsome type of input device and then followthe instructions in their programs todetermine the required output. The inputdevice may be a keyboard or a coolanttemperature sensor,

and the output may be video display or afuel injector. The program the computerfollows may be for word processing or forcontrolling fuel metering and enginetiming.

Computers can process a great deal ofdata very quickly and accurately, makingthem very useful for several jobsincluding controlling many of thesystems on an automobile. This chapterexplains how a computer functions,starting with the inputs and outputs, thecomputer's central processing unit (CPU)and memory, and logic gates and theirsymbols.

Understanding how computers work isessential because most vehicles havesome type of computer. Knowing howcomputers operate and fit together withvarious sensors and actuators willincrease your ability to diagnose andrepair problems.



This chapter is divided into the followingsections:

Analog and Digital InputsAnalog and Digital OutputsSignals, including.

Analog and digital wave formsAID convertersD/A converters

MicroprocessorRandom Access Memory (RAM)Read-Only Memory (ROM)Programmable Read-Only Memory

(PROM)Logic Circuits

INPUTS

As demonstrated in the previous chapter,the ECU, as well as any other automobilecomputer, depends on sensors to monitorvarious system functions and report theirstatus back to the computer. Once thecomputer receives the data from thesensors, it analyzes it against pre-programmed standards and actsaccordingly.

One problem with many of these inputs isthat they do not speak the same languageas the computer. The computer onlyunderstands digital signals or on/offsignals. A resistive type sensor providesthe computer

with a variable voltage, known as ananalog signal. Some sensors, like theswitch type sensors, do provide a digitalsignal for the computer. In this case, thecomputer can interpret the signalbecause it is either on or it is off-nothingin-between.

Because computers must have digitalinputs to use the data received, all analogsignals must be converted to digital. Howcomputers interpret the analog signalswith an A/D converter will be coveredlater.

OUTPUTS

Computer output to most actuators isdigital. The signal tells the actuator toeither turn on for a specified length oftime or shut off. Stepper motors, relaysand solenoids have only two modes ofoperation: on or off.

Again, when actuators require a variablevoltage, such as the speed control for ablower motor for air conditioning, thecomputer needs another interpreter. Inthis case, the interpreter is a D/Aconverter, which will be covered later.

SIGNALS

As explained previously, the two types ofsignals are analog and digital. Thevoltage of these signals may changeslowly or very quickly depending on thesensor and what it monitors. Whensignals are expressed as wave forms onan oscilloscope, the analog signal showsup as a flowing line with curved peaksand valleys, indicating variable rises anddrops in voltage. The digital signal hasvertical rises and drops, and a horizontalline with sharp corners. The tophorizontal lines indicate when the voltageis high or on and the bottom horizontallines indicate when the voltage is low oroff.



When using a voltmeter to measuredigital or analog signals that change veryquickly, such as speed sensor or RPMsignals, it is important to remember thatthe meter reading is not a truerepresentation of the signal. A voltmeterdisplays the average reading of thesignal. For example, with a digital signalthe voltmeter will display the averagebetween zero volts (off) and the voltagewhen the circuit was on. The computerlooks for "on" signals, not voltage. Thevoltmeter, however, is looking for voltage,not whether a signal comes through. Avoltmeter may show that the voltage iswithin specifications even if a pulse ismissing. That missing signal couldrepresent the cause of an engine problem.You might not know it by the voltmeter,causing you to assume incorrectly theproblem is elsewhere and waste timesearching.

So if you suspect the problem is in acertain circuit, but the voltmeter does notshow it, consider using an oscilloscopefor a more accurate reading. At the veryleast, you should be aware of thisvoltmeter limitation with digital signals.

When dealing with computer signals it isalso important to remember that there is

a difference between the signal sourceand the source of the voltage on the signalwire. This is especially important when asensor input goes to more than onecomputer, such as a speed sensor signal,or if the signal is from one computer toanother. One computer may supply thevoltage to the sensor which toggles thevoltage to ground, and the other computermay just monitor the signal. If a wire isdisconnected from the computer thatsupplies voltage to the sensor, the signalis lost to both computers. Do not mistakethis for a defective computer.

Analog signals also have limitations inthat their inputs are not usable by thecomputer until translated into digitalsignals. The A/D converter handles thattranslation.

This takes us briefly back to computerlanguage. Digital on/off can berepresented by the binary numberingsystem of 0 (off) and 1 (on). Any decimalnumber (1, 2, 3, etc.) can be representedusing O's and 1's so the computerunderstands. The several thousandtransistors inside the computer'smicroprocessor can switch on and off incombinations that equal any binarynumber in a microsecond.



The A/D converter changes the analogsignal to this binary language by takingsamples of the analog signal at afrequency known as the sampling rate.The converter measures the wave andassigns a digital value to it. The higherthe sampling rate, the closer the digitalsignal comes to representing the analogone. In most cases each sample is dividedinto eight bits. Each bit is assigned eithera "0" or a "1". These eight bits are called aword. As illustrated (below), wheneverthe A/D converter samples the signal, itassigns a binary number to the voltage atthat point (which the computer reads as aseries of "ONs" and "OFFs"), and slicesup the wave like a loaf of bread.

With the signal converted to eight-bitwords, the computer can use the datafrom the sensor. The computer thensends out instructions in the form of adigital signal to an actuator. In mostcases this works because most actuatorsare solenoids or stepper motors whichoperate on digital commands.

There are, however, some componentssuch as blower motors or the powersteering pump motor on the 1991 MR2,that require variable voltage to operatemotors at variable speeds. In such cases,the computer uses a D/A converter tochange the digital signal to analog. Theprinciples of D/A converter operation arethe same as the A/D converter. The

pulses of voltage coming from thecomputer are converted to variablevoltage.

THE MICROPROCESSORThe microprocessor is the heart of thecomputer. It is also called the centralprocessing unit (CPU). Again, keep inmind that the CPU does not performcomplicated operations. Instead, itperforms thousands of simple operationsincredibly fast. To keep all of theoperations the CPU performs frombecoming entangled, it executes them inorder, paced by a clock.

The CPU can be divided into threesections: the control section, thearithmetic and logic section, and theregister section.

The control section controls thecomputer's basic operations. It isprogrammed with instructions from amemory to handle these chief operations:

Sending data from one part of the computer toanotherData input and output to and from the computerArithmetic calculationsHalting computer operationsJumping to another instruction during therunning of a program

The arithmetic and logic section carriesout the actual processing of data, whichconsists of arithmetic operations andlogical operations.



The register section temporarily storesdata or programs until they are sent tothe arithmetic and logic section or thecontrol section

COMPUTER MEMORY

Computers have their own filing system,known as "memory," which is theinternal circuitry where programs anddata are stored. Computer memory isdivided into separate addresses to whichdata is sent y the CPU. The CPU thenknows where to find that data when it isneeded. Computers use their mainmemories for large amounts of data orprogram information. There are twokinds of memory: random accessmemory (RAM) and read-only memory(ROM).

RANDOM ACCESS MEMORY (RAM)

RAM is memory which the computer canboth read from and write to. This iswhere the computer stores data receivedfront sensors, such as engine RPM orcoolant temperature. RAM works likethousands of toggle switches which can

be either on or off to represent 0's and 1's.This is how the data is stored in RAM.The switches work like spring loadedswitches, therefore they must be held inthe on" position electrically. If power islost, everything stored in RAM is lost.

In most of the computers used onToyotas, the RAM is divided into twosections. One section receives its powerfrom the ignition switch. This is wheredata about operating conditions, such asvehicle speed and coolant temperature, isstored. The other section, called KeepAlive Memory, is powered directly by thebattery. Information such as diagnosticcodes is stored in Keep Alive Memory sothat it is retained after the ignition is off.This is why a fuse or battery cable has tobe removed to clear diagnostic codes.



READ-ONLY MEMORY (ROM)

This is where the basic operatinginstructions for the computer are located.The instructions are built into the chipwhen it is manufactured and cannot bechanged. The computer can only read theinformation located in ROM and cannotwrite to it or use it to store data. Since theinformation in ROM is built in duringmanufacture, it is not lost when power isremoved.

PROGRAMMABLE READ-ONLYMEMORY (PROM)

A PROM is like a ROM except it can beprogrammed or have information writtento it once. This is done before it isinstalled in the computer. The computercan only read from the PROM and cannotwrite to it. The PROM contains thespecific program instructions for thecomputer, such as the timing advancecurve for a particular engine or the shiftpoints for an automatic transmission.There are other types of programmableROM being used, such as erasableprogrammable read only memory(EPROM) which can be erased byultraviolet light and reprogrammed.Another type is electronically erasableprogrammable read only memory(EEPROM) which can be erasedelectronically and reprogrammed. This isall done outside of the computer by themanufacturer.

NON-VOLATILE MEMORY

Some computers use a type of RAM thatis non-volatile, meaning that it retains itsmemory when the power is removed.This type of memory can only be erased bygoing through a specific procedure. Thisis the type of memory used to store code 41in the SRS air bag system on Celica andSupra.

LOGIC CIRCUITS

As computers and solid state controlmodules become more prevalent onautomobiles, some of the logic gatesymbols that represent their

internal circuits will show up more often.It is necessary to know not only what thelogic symbols stand for, but to understandthe basic operation of the circuits theyrepresent when you analyze wiringdiagrams during troubleshooting.Therefore, you should know a little aboutlogic circuits and the symbols used torepresent them. A logic gate symbol issimply a shorthand way of representingan electronic circuit that operates in acertain way. Understanding the logicsymbols can make understanding theoperation of a circuit much quicker andeasier than if the circuit wererepresented by showing all thetransistors, diodes and resistors. Thelogic symbols shown in diagrams in theEWD and New Car Feature book showwhat pin voltages must be present for anelectronic controller to function properly.

Again, anything connected with acomputer is based on the digital on/offlanguage. The same holds true for logiccircuits, which are made up oftransistors combined in units called"gates." These gates process two or moresignals logically. In essence, they areswitches. Depending on the input voltage,the gate or switch will be either on or off.

The first thing to learn about the differentgates is their symbols. Once you know thesymbols and how each gate works,diagnosing a computer related problemwill be easier.



Taken with permission from theToyota Advanced Electrical Course#672




ASSIGNMENT NAME:

1. Explain both the purpose and different types of inputs used by the computer.

2. Name the type of output signal most often used by the computer.

3. Name the components that are typically used as output devices.

4. Explain the difference between Analog and Digital Signals.

5. Explain both the purpose and complete name of an A/D converter.

6. Draw both an Analog and Digital signal.

7. Explain the binary numbering system and why it is used.

8. Explain the function of the Microprocessor.

9. Describe the purpose of the RAM (Random Access Memory)

10. Describe the purpose of the ROM (Read Only Memory)

11. Describe the purpose of the PROM (Programmable Read Only Memory)

12. Explain the basic function and list the truth table of an “AND” logic gate circuit.

13. Draw the equivalent mechanical circuit of an “AND” logic gate circuit.

14. Explain the basic function and list the truth table of an “OR” logic gate circuit.

15. Draw the equivalent mechanical circuit of an “OR” logic gate circuit.

16. Describe the basic function and list the truth table of a “NOT” logic gate circuit.

17. Describe the basic function and list the truth table of a “NAND” logic gate circuit.

18. Describe the basic function and list the truth table of a “NOR” logic gate circuit.

19. Describe are the two basic components of a “FLIP-FLOP” logic gate circuit.

SENSORS AND ACTUATORS

Computer controlled systems continually monitor the operating condition of today's vehicles. Through sensors, computers receive vital information about a number of conditions, allowing minor adjustments to be made far more quickly and accurately than mechanical systems. Sensors convert temperature, pressure, speed, position and other data into either digital or analog electrical signals.

A digital signal is a voltage signal that is either on or off with nothing in between. A switch is the simplest type of digital signal sensor. The signal from the switch could be 0 volts when off and 12 volts when on. Analog signals on the other hand have continuously variable voltage. A good example is the coolant temperature sensor. The coolant temperature sensor may vary the voltage signal anywhere between 0 volts and 5 volts depending on the temperature of the engine.

SENSORS & ACTUATORS


The digital signal is the easiest for the computer to understand because it reads the signal as either "on" or "off." The analog signal must be conditioned or converted to digital so the computer can understand it. (This will be covered later.)

While a vehicle may have many different sensors, there are three main categories: voltage-generating, resistive and switches. A voltage-generating sensor generates its own voltage signal in relation to the mechanical condition it monitors. This signal in turn relays to the computer data about the condition of the system it controls. A resistive sensor reacts to changes in mechanical conditions through changes in its resistance. The computer supplies a regulated voltage or reference voltage to the sensor and measures the voltage drop across the sensor to determine the data.

Switch sensors toggle a voltage from the computer high or low, or supply an "on" or "off" voltage signal to the computer. This type of sensor may be as simple as a switch on the brake pedal or as complex as a phototransistor speed sensor.

The computer uses the sensor data to control different systems on a vehicle through the use of actuators. An actuator is an electromechanical device such as a relay, solenoid or motor. Actuators can adjust engine idle speed, change suspension height or regulate the fuel metered into the engine.

This chapter describes several specific sensors used in automobiles, such as potentiometers, thermistors and phototransistor / LED combinations. This chapter also addresses actuators that complete the control process by carrying out the computer's instructions.

The Sensors and Actuators section is divided into the following areas:

Resistive sensors: potentiometers thermistors piezo resistive

Voltage generating sensors: piezo electric zirconia-dioxide magnetic inductance

Switch sensors: phototransistors and LEDs speed sensors G-sensors (Air Bag Impact Sensors)

Actuators: stepper motors solenoids

RESISTIVE SENSORS

Potentiometers

A potentiometer is a variable resistor that is commonly used as a sensor. A potentiometer has three terminals: one for power input, one for a ground and one to provide a variable voltage output. A potentiometer is a mechanical device whose resistance can be varied by the position of the movable contact on a fixed resistor. The movable contact slides across the resistor to vary the resistance and as a result varies the voltage output of the potentiometer. The output becomes higher or lower depending on whether the movable contact is near the resistor's supply end or ground end.

SENSORS & ACTUATORS


The vane type air flow meter on an EFI equipped vehicle is a common location on a Toyota for a sensor that uses a potentiometer. This sensor converts the air flow meter vane opening angle to a voltage and sends it to the Electronic Control Unit (ECU). This signal allows the ECU to determine the volume of air that is entering the engine.

Some models also use a potentiometer as the throttle position sensor. The potentiometer in this case is attached to the throttle shaft of the throttle body. As the shaft is rotated the voltage output of the potentiometer changes. The voltage output of the potentiometer supplies data to the ECU about the throttle opening angle.

Thermistors

Thermistors are variable resistors whose resistance changes in relation to temperature. Thermistors can have either a negative temperature coefficient (NTC) or a positive temperature coefficient (PTC). A thermistor with a negative temperature coefficient will decrease in resistance as the temperature is increased. On the other hand, a thermistor with a positive temperature coefficient will increase in resistance as the temperature is increased. The thermistor has two terminals, one for power and one for ground. A reference voltage is supplied to one terminal through a fixed series resistor located inside the computer. The other terminal of the thermistor is connected to ground, usually back through the computer. The computer monitors the voltage after the internal fixed resistor and compares this voltage to the reference voltage to determine the temperature of the thermistor. The relationship between the two voltages changes as the temperature of the thermistor changes.

SENSORS & ACTUATORS


The coolant temperature sensor and the air temperature sensor in the air flow meter are both NTC thermistors. Thermistors are also used as sending units for temperature gauges such as the coolant temperature gauge. The TCCS ECU uses data from the coolant temperature sensor and air temperature sensor to help determine the proper amount of fuel and how long to open the fuel injectors. The ECU also uses this data to determine how much the ignition timing should be advanced as well as the proper setting for the ISC to maintain the proper idle speed. When either the air temperature or the coolant temperature is low, the respective thermistor's resistance increases and the computer receives a high voltage signal at the respective sensor wire. Conversely, a high temperature at either sensor results in a low voltage signal due to the lower resistance of the thermistor.

Piezo ResistiveA piezo resistive sensor is a resistor circuit constructed on a thin silicon wafer. Physically flexing or distorting the wafer a small amount changes its resistance. This type of sensor is usually used as a pressure sensing device such as a manifold pressure sensor, although it may also be used to measure force or flex in an object such as the deceleration sensor located in the SRS air bag center sensor.

One of the most important piezo resistive sensors is the manifold pressure sensor which monitors the air intake volume for Electronic Fuel Injection (EFI). The signal it sends to the ECU determines the basic fuel injection duration and ignition advance angle.

Within the sensor is a silicon chip combined with a vacuum chamber. One side of the chip is exposed to the intake manifold pressure and the other side to the internal perfect vacuum in the chamber.

A change in the intake manifold pressure causes the shape of the silicon chip to change, with the resistance value of the chip fluctuating in relation to the degree of deformation. An integrated circuit converts the fluctuation to a voltage signal that is sent to the ECU, where the air-fuel ratio is regulated. The sensor has three external terminals: one for power, one for ground and one to provide the voltage signal to the computer. The voltage signal varies with the pressure in the intake manifold.

Another use for this same type of sensor is to sense turbocharger boost. On turbocharged engines, the sensor is used to measure pressures that are higher than atmospheric pressure and to supply corresponding voltage signals to the ECU. To prevent engine damage, the ECU can cut off the fuel being injected if the manifold pressure becomes too high.

SENSORS & ACTUATORS


VOLTAGE GENERATING SENSORS

Piezo Electric

Piezo electricity is generated by pressure on certain crystals, such as quartz, which will develop a potential difference, or voltage, on the crystal face. When the crystal flexes or vibrates, an AC voltage is produced.

Knock sensors, which are becoming more common, take advantage of this phenomenon by sending the ECU a signal that engine knock is occurring. The ECU in turn retards the ignition timing to stop the knocking. Knock sensors contain a piezo electric element which, when deformed by cylinder block vibration caused by knocking, generates a voltage.

There are two styles of knock sensors used. The mass type produces a voltage output over wide range, but the signal is greatest at a vibration of approximately 7 kHz. The other style is the resonance type which only produces a significant voltage signal when exposed to a vibration of approximately 7 kHz. Since the voltage output from either knock sensor varies continually, the system is highly susceptible to electromagnetic andradio interference. The computer can be

fooled by these stray electrical signals if they get mixed with the knock sensor signal. For this reason the signal wire running from the sensor to the ECU is a special ground-shielded type. The shield surrounds the signal wire and is connected to ground so any electrical interference is taken to ground. If this shield is damaged or not grounded, the electrical interference can reach the ECU and cause it to retard the timing unnecessarily.

Oxygen Sensors

The oxygen sensor, located in the exhaust manifold, senses whether the air-fuel ratio is rich or lean, and sends signals to the ECU which in turn makes minor corrections to the amount of fuel being metered. This is necessary for the three-way catalytic converter to function properly.

There are two kinds of oxygen sensors: zirconia and titania. The zirconia oxygen sensor is constructed in a bulb configuration from zirconia dioxide. A thin platinum plate is attached to both the inside and outside of the bulb. The inner area is exposed to the atmosphere and the outside is exposed to the exhaust. When the sensor is heated to approximately 600˚F, electrically

SENSORS & ACTUATORS


charged oxygen ions form on the platinum plates. The amount of oxygen to which each plate is exposed determines how many ions form on the plates. When there is a difference in the number of ions on the plates, a difference in potential or voltage occurs between the two plates. The less oxygen there is in the exhaust, the greater the voltage produced. When the air-fuel mixture is lean, the voltage created is low. Conversely, when the mixture is rich, the voltage is high.

The titania oxygen sensor does not produce a voltage. Instead, it undergoes a change in resistance in relation to the oxygen content in the exhaust. This type of oxygen sensor is referred to as a thick film sensor. It consists of a piece of titania with two wires connected to it located at the end of an insulator. The sensor is not exposed to the atmosphere only to the exhaust. Because the operating temperature must remain constant, the sensor has an electric heater. After the

sensor is at operating temperature, the amount of oxygen to which the titania is exposed. will change the physical resistance of the sensor. The ECU supplies a reference voltage to the sensor and monitors the voltage at the signal wire, similar to a thermistor.

Magnetic InductanceMagnetic inductance sensors consist of a coil of wire around an iron core plus a permanent magnet. The magnet can be either stationary or movable. If the magnet is the moving member, as it passes the coil the magnetic lines of force cut through the coil and a voltage is produced. Since the north and south poles of the magnet alternate as they pass the coil, the voltage polarity also alternates. As the speed of the magnet rotating past the coil is increased a larger voltage is produced and the frequency of the voltage polarity changes is increased. This same type of sensor can also work if the magnet is stationary and attached to the core of the coil. When a toothed reluctor, or rotor (made from a magnetic material) is rotated past the coil and magnet, the magnetic lines of force move and cut through the coil. The lines of force cutting through the coil will produce the same type of voltage output as when the magnet was moving.

SENSORS & ACTUATORS


This type of sensor is commonly used as a wheel speed sensor on ABS equipped vehicles. This sensor is also used in the distributor to determine RPM and crankshaft position. Since the voltage output of this sensor is varying continually and is low at low speeds, the computer must be able to sense the small voltage. If electrical interference is allowed to combine with the signal voltage, the computer could be fooled. To prevent stray electrical interference, the signal wire usually has a ground shield formed around it like the knock sensor.

SWITCH TYPE SENSORS

Phototransistor and LED

As discussed in the previous chapter, a phototransistor is a transistor that is activated or turned on by light. When combined with a LED and a rotating slotted wheel in a vehicle speed sensor, a phototransistor can supply vehicle speed data to a computer.

In this type of sensor the LED is aimed at the phototransistor. When the slotted wheel is rotated by the speedometer cable, it breaks

the beam of light. The beam of light is interrupted 20 times per revolution. The ECU supplies a reference voltage to the collector of the phototransistor and the emitter is connected to ground. Each time the light hits the phototransistor, it turns it on just like a toggle switch. Each time the phototransistor is turned on, the wire from the ECU is connected to ground and the voltage is pulled down to 0 volts. The ECU can count these pulses and calculate vehicle speed.

This type of sensor is also used as a G Sensor or deceleration sensor on the Celica All Trac and Trucks equipped with ABS. This sensor has two LEDs aimed at two phototransistors that are separated by a slotted plate on a fulcrum. When the vehicle is decelerated, the plate pivots on the fulcrum and the slots in the plate line up with one or the other or both of the LEDs and phototransistors-depending on the rate of deceleration. These signals are sent to the computer so it can determine the deceleration rate for ABS to operate properly.

SENSORS & ACTUATORS


Reed Switches

The reed switch is commonly used as a speed sensor or position sensor. It consists of a set of contacts that open when adjacent to a magnet. In the speed sensor application, the magnet is attached to the speedometer cable and rotates with the cable. Each time one of the poles of the magnet passes the switch the contacts open and then close. A voltage is supplied to one contact on the switch and the other contact is connected to ground. Each time the points close, the voltage is pulled down to 0 volts, just like the phototransistor speed sensor.

ACTUATORS

Stepper Motor

Essentially, stepper motors are digital actuators; in other words, they are either on or off. They move in fixed increments in both directions, and can have over 120 steps of motion.

Stepper motors are commonly used to enable the ECU to control idle speed. In most fuel injection systems, the stepper motor controls an idle air bypass built into the throttle body.

SENSORS & ACTUATORS


In an idle speed control valve (ISCV), (located in the air intake chamber) a stepper motor is built into the ISCV where it rotates a valve shaft either in or out. This in turn increases or decreases the clearance between the valve and the valve seat, thereby regulating the amount of air allowed to pass through. The ISCV stepper motor allows 125 possible valve opening positions.

Solenoids

Like stepper motors, solenoids are digital actuators. One terminal is attached to battery voltage while the other is attached to the computer which opens and closes the ground circuit as needed. When energized, the solenoid may extend a plunger or armature to control functions such as vacuum flow to various emission-related systems or fuel injection. Most actuators are solenoids.

Solenoids are controlled two ways: pulse width or duty cycle. Pulse width control is used when the frequency is not consistent. An example of pulse width is a fuel injector which is turned on for a determined length of time and then shut off. Duty cycle control is used when the frequency does remain constant. A duty cycle solenoid in ABS is designed to be on and off for a specific time according to a selected ratio-on for 20% of the time and off the other 80%.

Idle speed control valves can be constructed with a solenoid instead of a stepper motor. In this case, the function is the same: the ECU sends a signal to the ISCV to control the intake air.

Solenoid valves are also used in ECT transmissions. Shifting is controlled by the solenoid as it opens or closes a hydraulic passage to control oil flow to the shift valves.

SENSORS & ACTUATORS


SENSORS & ACTUATORS

ASSIGNMENT NAME:

1. Describe the term “Digital Signal” and provide an example.

2. List three types of “Resistive senors” and provide an example of each.

3. List three “types of Voltage generating sensors” and provide an example of each.

4. List three types of “Switch sensors” and provide an example of each.

5. List two types of “Actuators” and provide an example of each.

6. Describe the operation of both types of “thermistors” and draw an example of the electrical circuit.

7. Explain the operation of a “Piezo Resistive” sensor.

8. Explain how a “Piezo Resistive” sensor differs from a “Piezo Electric” sensor.

9. Describe the operation and construction of the two basic types of Oxygen Sensors.

10. Outline the construction and common uses of a “Magnetic Inductance” sensor.

11. Outline the construction and common uses of a “Phototransistor” switch.

12. Explain the operation of a “Reed” switch and how they are used.

13. Describe the basic operation of a “stepper motor” and how they are used.

14. Explain two ways in which solenoids can be controlled.

Electronic Control Transmission (ECT)The Electronic Control Transmission is an automatic transmission which uses modern electronic control technologies to control the transmission. The transmission itself, except for the valve body and speed sensor, is virtually the same as a full hydraulically controlled transmission, but it also consists of electronic parts, sensors, an electronic control unit and actuators.

The electronic sensors monitor the speed of the vehicle, gear position selection and throttle opening, sending this information to the ECU. The ECU then controls the operation of the clutches and brakes based on this data and controls the timing of shift points and torque converter lock-up.

Driving Pattern Select SwitchThe pattern select switch is controlled by the driver to select the desired driving mode, either "Normal" or "Power." Based on the position of the switch, the ECT ECU selects the shift pattern and lock-up accordingly. The upshift in the power mode will occur later, at a higher speed depending on the throttle opening. For example, an upshift to third gear at 50% throttle will occur at about 37 mph in normal mode and about 47 mph in power mode.

TOYOTA ELECTRONIC CONTROL TRANSMISSION


The ECU has a "PWR" terminal but does not have a "Normal" terminal. When "Power" is selected, 12 volts are applied to the "PWR" terminal of the ECU and the power light illuminates. When "Normal" is selected, the voltage at "PWR" is 0 volts. When the ECU senses 0 volts at the terminal, it recognizes that "Normal" has been selected.

Beginning with the 1990 MR2 and Celica and the 1991 Previa, the pattern select switch was discontinued. In the Celica and Previa systems, several shift patterns are stored in the ECU memory. Utilizing sensory inputs, the ECU selects the appropriate shift pattern and operates the shift solenoids accordingly. The MR2 and 1993 Corolla have only one shift pattern stored in the ECU memory.

Neutral Start SwitchThe ECT ECU receives information on the gear range into which the transmission has been shifted from the shift position sensor, located in the neutral start switch, and determines the appropriate shift pattern. The neutral start switch is actuated by the manual valve shaft in response to gear selector movement.

The ECT ECU only monitors positions "T' and "L." If either of these terminals provides a 12-volt signal to the ECU, it determines that the transmission is in neutral, second gear or first gear. If the ECU does not receive a 12-volt signal at terminals "T' or "1," the ECU determines that the transmission is in the "D" range.

Some neutral start switches have contacts for all gear ranges. Each contact is attached to the gear position indicator lights if the vehicle is so equipped.



In addition to sensing gear positions, the neutral switch prevents the starter from cranking the engine unless it is in the park or neutral position. In the park and neutral position, continuity is established between terminals "B" and "NB" of the neutral start switch illustrated below.

Throttle Position SensorThis sensor is mounted on the throttle body and electronically senses how far the throttle is open and then sends this data to the ECU. The throttle position sensor takes the place of throttle pressure in a fully hydraulic control transmission. By relaying the throttle position, it gives the ECU an indication of engine load to control the shifting and lock-up timing of the transmission.

There are two types of throttle sensors associated with ECT transmissions. The type is related to how they connect to the ECT ECU. The first is the indirect type because it is connected directly to the engine ECU, and the engine ECU then relays throttle position information to the ECT ECU. The second type is the direct type which is connected directly to the ECT ECU.



Indirect TypeThis throttle position sensor converts the throttle valve opening angle into voltage signals. It has four terminals: VC, VTA, IDL and E. A constant 5 volts is applied to terminal VC from the engine ECU. As the contact point slides along the resistor with throttle opening, voltage is applied to the VTA terminal. This voltage increases linearly from 0 volts at closed throttle to 5 volts at wide-open throttle.

The engine ECU converts the VTA voltage into one of eight different throttle opening angle signals to inform the ECT ECU of the throttle opening. These signals consist of various combinations of high and low voltages at ECT ECU terminals as shown in the chart below. The shaded areas of the chart represent low voltage (about 0 volts). The white areas represent high voltage (L1, L2, U: about 5 volts; IDL: about 12 volts).



When the throttle valve is completely closed, the contact points for the IDL signal connect the IDL and E terminals, sending an IDL signal to the ECT ECU to inform it that the throttle is fully closed.

As the ECT ECU receives the L1, L2 and D signals, it provides an output voltage from 1 to 8 volts at the TT or ECT terminal of the diagnostic check connector. The voltage signal varies depending on the throttle opening angle and informs the technician whether or not the throttle opening signal is being input properly.

Direct TypeWith this type of throttle sensor, signals are input directly to the ECT ECU from the throttle position sensor. Three movable contact points rotate with the throttle valve, causing contacts L1, L2, L3 and IDL to make and break the circuit with contact E (ground). The grid which the contact points slide across is laid out in such a way as to provide signals to the ECT ECU depicted in the chart below. The voltage signals provided to the ECT ECU indicate throttle position just as they did in the indirect type of sensor.

If the idle contact or its circuit on either throttle sensor malfunctions, certain symptoms occur. If it is shorted to ground, lock-up of the torque converter will not occur. If the circuit is open, neutral to drive squat control does not occur and a harsh engagement may be the result. If the L1, L2, L3 signals are abnormal, shift timing will be incorrect.



Water Temperature SensorThe water temperature sensor monitors engine coolant temperature and is typically located near the cylinder head water outlet. A thermistor is mounted within the temperature sensor, and its resistance value decreases as the temperature increases. Therefore, when the engine temperature is low, resistance will be high.

When the engine coolant is below a predetermined temperature, the engine performance and the vehicle's drivability would suffer if the transmission were shifted into overdrive or the converter clutch were locked-up. The engine ECU monitors coolant temperature and sends a signal to terminal OD1 of the ECT ECU. The ECU prevents the transmission from upshifting into overdrive and lock-up until the coolant has reached a predetermined temperature. This temperature will vary from 122'F to 162’F depending on the transmission and vehicle model. For specific temperatures, refer to the ECT Diagnostic Information chart in the appendix of this book.

Some models, depending on the model year, cancel upshifts to third gear at lower temperatures. This information is found in the appendix and is indicated in the heading of the OD Cancel Temp column of the ECT Diagnostic Information chart by listing in parenthesis the temperature for restricting third gear.



Speed SensorsTo ensure that the ECT ECU is kept informed of the correct vehicle speed at all times, vehicle speed signals are input into it by two speed sensors. For further accuracy, the ECT ECU constantly compares these two signals to see whether they are the same. The speed sensor is used in place of governor pressure in the conventional hydraulically controlled transmission.

Main Speed Sensor (No. 2 Speed Sensor)The main speed sensor is located in the transmission housing. A rotor with built-in magnet is mounted on the drive pinion shaft or output shaft. Every time the shaft makes one complete revolution, the magnet activates the reed switch, causing it to generate a signal. This signal is sent to the ECU, which uses it in controlling the shift point and the operation of the lock-up clutch. This sensor outputs one pulse for every one revolution of the output shaft.

Beginning with the 1993 Corolla A245E, the No. 2 speed sensor has been discontinued and only the No. 1 speed sensor is monitored for shift timing.



Back- Up Speed Sensor (No.1 Speed Sensor)The back-up speed sensor is built into the combination meter assembly and is operated by the speedometer cable. The sensor consists of an electrical reed switch and a multiple pole permanent magnet assembly. As the speedometer cable turns, the permanent magnet rotates past the reed switch. The magnetic flux lines between the poles of the magnet cause the contacts to open and close as they pass. The sensor outputs four pulses for every one revolution of the speedometer cable.

The sensor can also be a photocoupler type which uses a photo transistor and light-emitting diode (LED). The LED is aimed at the phototransistor and separated by a slotted wheel. The slotted wheel is driven by the speedometer cable. As the slotted wheel rotates between the LED and photo diode, it generates 20 light pulses for each rotation. This signal is converted within the phototransistor to four pulses sent to the ECU.

Speed Sensor FailsafeIf both vehicle speed signals are correct, the signal from the main speed sensor is used in shift timing control after comparison with the output of the back-up speed sensor. If the signals from the main speed sensor fail, the ECU immediately discontinues use of this signal and uses the signals from the back-up speed sensor for shift timing.



Stop Light SwitchThe stop light switch is mounted on the brake pedal bracket. When the brake pedal is depressed, it sends a signal to the STP terminal of the ECT ECU, informing it that the brakes have been applied.

The ECU cancels torque converter lock-up when the brake pedal is depressed, and it cancels "N" to "D" squat control when the brake pedal is not depressed and the gear selector is shifted from neutral to drive.

Overdrive Main SwitchThe overdrive main switch is located on the gear selector. It allows the driver to manually control overdrive. When it is turned on, the ECT can shift into overdrive. When it is turned off, the ECT is prevented from shifting into overdrive.



O/D Main Switch ONWhen the O/D switch is in the ON position, the electrical contacts are actually open and current from the battery flows to the OD2 terminal of the ECT ECU as shown below.

O/D Main Switch OFFWhen the O/D switch is in the OFF position, the electrical contacts are actually closed and current from the battery flows to ground and 0 volts is present at the OD2 terminal as shown below. At the same time, the O/D OFF indicator is illuminated.

Solenoid ValvesSolenoid valves are electro-mechanical devices which control hydraulic circuits by opening a drain for pressurized hydraulic fluid. Of the solenoid valves, No. 1 and No. 2 control gear shifting while No. 3 controls torque converter lock-up.



No. 1 and No. 2 Solenoid Valves These solenoid valves are mounted on the valve body and are turned on and off by electrical signals from the ECU, causing various hydraulic circuits to be switched as necessary. By controlling the two solenoids' on and off sequences, we are able to provide four forward gears as well as prevent upshifts into third or fourth gear.

The No. 1 and No. 2 solenoids are normally closed. The plunger is spring loaded to the closed position, and when energized, the plunger is pulled up, allowing line pressure fluid to drain. The operation of these solenoids by the ECT ECU is described on pages 16- 19.

No. 3 Solenoid ValveThis solenoid valve is mounted on the transmission exterior or valve body. It controls line pressure which affects the operation of the torque converter lock-up system. This solenoid is either a normally open or normally closed solenoid. The A340E, A340H, A540E and A540H transmissions use the normally open solenoid.

No. 4 Solenoid ValveThis solenoid is found exclusively on the A340H transfer unit described on page 152 of this book. This solenoid is a normally closed solenoid which controls the shift to low 4-wheel drive. It is controlled by the ECT ECU when low 4-wheel drive has been selected at vehicle speeds below 18 mph with light throttle opening.



Functions of ECT ECU

Control of Shift Timing

The components which make up this system include:

• OD main switch • OD Off indicator light • ECT ECU • Water temperature sensor • Cruise control ECU • No. 1 and No. 2 solenoid valves (shift solenoids)

The ECU controls No. 1 and No. 2 solenoid valves based on vehicle speed, throttle opening angle and mode select switch position.

The ECT ECU prevents an upshift to overdrive under the following conditions:

• Water temperature is below 122'F to 146*F*. • Cruise control speed is 6 mph below set speed. • OD main switch is off (contacts closed).

In addition to preventing the OD from engaging below a specific engine temperature, upshift to third gear is also prevented in the Supra and Cressida below 96'F and the V6 Camry below 100’F.

* Consult the specific repair manual or the ECT Diagnostic Information Technician Reference Card for the specific temperature at which overdrive is enabled.



Control of Lock-UpThe ECT ECU has lock-up clutch operation pattern for each driving mode (Normal and Power) programmed in its memory. The ECU turns the No. 3 solenoid valve on or off according to vehicle speed and throttle opening signals. The lock-up control valve changes the fluid passages for the converter pressure acting on the torque converter piston to engage or disengage the lock-up clutch.

In order to turn on solenoid valve No. 3 to operate the lock-up system, the following three conditions must exist simultaneously:

• The vehicle is traveling in second, third, or overdrive ("D" range).

• Vehicle speed is at or above the specified speed and the throttle opening is at or above the specified value.

• The ECU has received no mandatory lock-up system cancellation signal.

The ECU controls lock-up timing in order to reduce shift shock. If the transmission up-shifts or down-shifts while the lock-up is in operation, the ECU deactivates the lock-up clutch.



The ECU will cancel lock-up if any of the following conditions occur:

• The stop light switch comes on.

• The coolant temperature is below 122'F to 145’F depending on the model. Consult the vehicle repair manual or the ECT Diagnostic Information Technician Reference Card.

• The IDL contact points of the throttle position sensor close.

• The vehicle speed drops about 6 mph or more below the set speed while the cruise control system is operating.

The stop light switch and IDL contacts are monitored in order to prevent the engine from stalling in the event that the rear wheels lock up during braking. Coolant temperature is monitored to enhance drivability and transmission warm-up. The cruise control monitoring allows the engine to run at higher rpm and gain torque multiplication through the torque converter.

Neutral to Drive Squat ControlWhen the transmission is shifted from the neutral to the drive range, the ECU prevents it from shifting directly into first gear by causing it to shift into second or third gear before it shifts to first gear. It does this in order to reduce shift shock and squatting of the vehicle.

Engine Torque ControlTo prevent shifting shock on some models, the ignition timing is retarded temporarily during gear shifting in order to reduce the engine's torque. The TCCS and ECT ECU monitors engine speed signals (Ne) and transmission output shaft speed (No. 2 speed sensor) then determines how much to retard the ignition timing based on shift pattern selection and throttle opening angle.



Fail-Safe OperationThe ECT ECU has several fail-safe functions to allow the vehicle to continue operating even if a malfunction occurs in the electrical system during driving. The speed sensor fail-safe has already been discussed on page 8.

Solenoid Valve Back-Up FunctionIn the event that the shift solenoids malfunction, the ECU can still control the transmission by operating the remaining solenoid to put the transmission in a gear that will allow the vehicle to continue to run.

The chart below identifies the gear position the ECU places the transmission if a given solenoid should fail. Notice that if the ECU was not equipped with fail-safe, the items in parenthesis would be the normal operation. But because the ECU senses the failure, it modifies the shift pattern so the driver can still drive the vehicle. For example, if No. 1 solenoid failed, the transmission would normally go to overdrive in drive range first gear. But instead, No. 2 solenoid turned it on to give 3rd gear.

Should both solenoids malfunction, the driver can still safely drive the vehicle by operating the shift lever manually.



ECT Shift Valve OperationTwo electrically operated solenoids control the shifting of all forward gears in the Toyota electronic control four speed automatic transmission. These solenoids are controlled by an ECU which uses throttle position and speed sensor input to determine when the solenoids are turned on. The solenoids normal position is closed, but when it is turned on, it opens to drain fluid from the hydraulic circuit. Solenoid No. 1 controls the 2-3 shift valve. It is located between the manual valve and the top of the 2-3 shift valve. Solenoid No. 2 controls the 1-2 shift valve and the 3-4 shift valve.

First GearDuring first gear operation, solenoid No. 1 is on and solenoid No. 2 is off. With line pressure drained from the top of the 2-3 shift valve by solenoid No. 1, spring tension at the base of the valve pushes it upward. With the shift valve up, line pressure flows from the manual valve through the 2-3 shift valve and on to the base of the 3-4 shift valve.

With solenoid No. 2 off, line pressure pushes the 1-2 shift valve down. In this position, the 1-2 shift valve blocks line pressure from the manual valve. Line pressure and spring tension at the base of the 3-4 shift valve push it upward.



Second GearDuring second gear operation, solenoid No. 1 and No. 2 are on. Solenoid No. 1 has the same effect that it had in first gear with the 2-3 shift valve being held up by the spring at its base. Pressure from the manual valve flows through the 2-3 shift valve and holds the 3-4 shift valve up.

With solenoid No. 2 on, line pressure from the top of the 1-2 shift valve bleeds through the solenoid. Spring tension at the base of the 1-2 shift valve pushes it upward. Line pressure which was blocked, now is directed to the second brake (132), causing second gean The 3-4 shift valve maintains its position with line pressure from the 2-3 shift valve holding it up.



Third GearDuring third gear operation, solenoid No. 1 is off and solenoid No. 2 is on. When solenoid No. 1 is off, it closes its drain and line pressure from the manual valve pushes the 2-3 shift valve down. Line pressure from the manual valve is directed to the direct clutch (C2) and to the base of the 1-2 shift valve.

With solenoid No. 2 on, it has the same effect that is had in second gear; pressure is bled at the top of the 1-2 shift valve and spring tension pushes it up. Line pressure is directed to the second brake (B2). However in third gear, the second brake (B2) has no effect since it holds the one-way clutch No. 1 (Fl) and freewheels in the clockwise direction. The second coast brake is ready in the event of a downshift when the OD direct clutch (C2) is released.



Fourth GearDuring fourth gear operation, both solenoids are off. When solenoid No. 1 is off, its operation is the same as in second and third gears.

A third solenoid controls lock-up operation.

Reprinted with permission by Toyota Motor Sales, USA, Inc.,from the Automatic Transmission Course #262 textbook.



Checks and AdjustmentsThe transmission requires regular maintenance intervals if it is to continue to operate without failure. As we discussed in previous sections, transmission fluid loses certain properties over time and especially due to heat.

The Maintenance Schedules found in the repair manual or the Owners Manual indicate the appropriate replacement schedules based on how the vehicle is used. Schedule A for example, recommends replacement of the fluid every 20,000 miles or 24 months. Whereas Schedule B recommends just an inspection of the fluid every 15,000 miles or 24 months and no replacement interval.

The chart below indicates which maintenance schedule to follow based on the use of the vehicle.

TOYOTA ELECTRONIC TRANSMISSION CHECKS & DIAGNOSIS


Fluid LevelThe fluid level in the automatic transmission should be inspected by means of the dipstick after the transmission has been warmed up to ordinary operating temperature, approximately 158'F to 176'F. As a rule of thumb, if the graduated end is too hot to hold, the fluid is at operating temperature. The fluid level is proper if it is in the hot range between hot maximum and hot minimum.

NOTE: The cool level found on the dip stick should be used as a reference only when the transmission is cold. The correct fluid level can only be found when the fluid is hot.

It is important to keep the fluid at the correct level at all times to ensure proper operation of the automatic transmission. If the fluid level is too low, the oil pump will draw in air, causing air to mix with the fluid. Aerated fluid lowers the hydraulic pressure in the hydraulic control system, causing slippage and resulting in damage to clutches and bands. If the fluid level is excessive, planetary gears and other rotating components agitate the fluid, aerating it and causing similar symptoms as too little fluid. In addition, aerated fluid will rise in the case and may leak from the breather plug at the top of the transmission or through the dipstick tube.

In addition, be sure to check the differential fluid level in a transaxle. This fluid is sealed off and separate from the transmission cavity in some applications.



Throttle CableThe throttle cable is adjustable on all automatic transmissions. And in each case it controls throttle pressure. Throttle pressure is an indication of load. When the throttle is depressed, the cable transfers this motion to the base of the throttle valve and moves it upward to increase throttle pressure. Throttle pressure causes the primary regulator valve to increase line pressure. As the throttle is depressed, greater torque is produced by the engine and the transmission may also downshift to a lower gear. If line pressure did not increase, slippage could occur which would result in wear of the clutch plate surface material.

Throttle pressure's affect on transmission operation differs between a hydraulically controlled transmission (non-ECT) and an electronically controlled transmission (ECT). In a non-ECT transmission, throttle pressure affects shift points and line pressure; whereas in an ECT transmission it only affects line pressure. Control of line pressure will affect the quality of the shift, not the shift points, in an ECT transmission.



Inspect and Adjust the Throttle Cable To inspect the throttle cable adjustment, the engine should be off. Depress the accelerator pedal completely, and make sure that the throttle valve is at the maximum open position. If the throttle valve is not fully open, adjust as needed.

With the throttle fully open, check the throttle cable stopper at the boot end and ensure that there is no more than one millimeter between the end of the stopper and the end of the boot. If adjustment is required, make the adjustment with the throttle depressed. Loosen the locking nuts on the cable housing and reposition the cable housing and boot as needed until the specification is reached.

The Land Cruiser A440 automatic transmission throttle cable is adjusted differently, as seen below. It is measured in two positions. The first measurement is made with the throttle fully closed. The distance varies in that the measurement is made from the end of the boot to the front of the stopper. Measure the same distance with the throttle in the fully open position.

The illustration below represents yet another adjustment type. The rubber boot has a shallow extension when compared to the first one discussed earlier. The procedure differs in that the throttle is left in the fully closed position when the distance is measured from the front of the boot to the front of the stopper.



Inspect and Adjust the Shift Cable To inspect the shift cable, move the gear selector from neutral to each position. The gear selector should move smoothly and accurately to each gear position. Adjust the shift cable in the indicator does not line-up with the position indicator while in the proper detent. To adjust, loosen the swivel nut on the shift linkage. Push the manual lever at the transmission fully toward the torque converter end of the transmission. Then pull the lever back two notches from Park through Reverse to the Neutral position. Set the selector level to the Neutral position and tighten the swivel nut while holding the lever lightly toward the reverse position.

Check Idle Speed and Adjust if ApplicableIdle speed is an important aspect for transmission engagement. If set too high, when shifting from neutral to drive or reverse, the engagement will be too abrupt, causing not only driver discomfort, but also affecting the components of the transmission as well. And, of course, if the idle is too low, it may cause the engine to stall or idle roughly.

To adjust the idle speed:

• The engine should be at operating temperature.

• All accessories should be off.

• Set the parking brake.

• Place the transmission in park or neutral position.

• Engine cooling fan should be off.



DiagnosisDuring diagnosis, always verify the customer complaint. If the verification includes a test drive, be sure to check the level of ATF first. This will ensure that a low level is not contributing to the problem and give you an idea as to the condition and service that the vehicle has seen. Although preliminary checks suggest making adjustments, drive the vehicle before any adjustments in order to experience the same condition as the customer. If you are unable to verify the problem, ask the customer to accompany you on the test drive and point-out when the condition occurs.

When test driving a vehicle, have a plan and record your findings. The chart that follows is quite thorough and provides room for comments. Rather than trying to remember the results of a specific test, simply refer to the diagnostic form. Not only do you want to find out what has failed, but also what is functioning properly. Armed with this information, you will save time in your diagnosis and be more thorough.



Road Test - Automatic Transmission



For example, if the transmission does not slip while accelerating from a stop with wide open throttle, line pressure is sufficient. If shift points occur at the proper speeds, throttle pressure and governor pressure are sufficient. Or for ECT transmissions, throttle sensor and speed sensor inputs are being received by the ECU and the circuit and solenoids are working properly.

Upshift quality is important to consider during the road test because it is an indicator of proper line pressure and accumulator operation. If all upshifts are harsh, it indicates a common problem such as line pressure and should be verified with a pressure test. If a harsh upshift is evident in a specific gear, check the accumulator which is associated with the holding device for that specific gear.

Following the road test, compare your findings with the troubleshooting matrix chart in the repair manual. (An example can be found on page 15.) The matrix chart will assist you in identifying components or circuits which can be repaired while the transmission is mounted in the vehicle. Or identify the components which should be inspected with the transmission on the bench.

Based on your diagnosis, if the transmission can be repaired with an on vehicle repair, the off-vehicle repair should be attempted first. Should the transmission require removal from the vehicle, a remanufactured transmission should be evaluated against the cost of an in-house overhaul.

Electrical Diagnostic Testing

Onboard DiagnosticsThe ECU is equipped with a built-in self diagnostic system, which monitors the speed sensors, solenoid valves and their electrical circuitry. If the ECU senses a malfunction:

1. It blinks the OD OFF light to warn the driver.

2. It stores the malfunction code in its memory.

3. (When properly accessed) it will output a diagnostic code indicating the faulty component or circuit.



Once a malfunction is stored in the memory system, it will be retained until canceled (erased). The vehicle battery constantly supplies 12 volts to the ECU B terminal to maintain memory even if the ignition switch is turned off. If the malfunction is repaired or returns to normal operation, the warning light will go off but the malfunction code will remain in memory. In order to erase a diagnostic code from the memory, a specified fuse must be removed for approximately 30 seconds with the ignition switch is off. The fuse is identified in the repair manual or on the ECT Diagnostic Information technician reference card.

Throttle Position Sensor SignalIn order to determine if the throttle position sensor signal and brake switch signal are being received by the ECU, place the ignition switch to the ON position with the engine off, connect a digital voltmeter to the diagnostic check connector and slowly depress the throttle. On models prior to 1987, if the vehicle does not have a diagnostic check connector in the engine compartment, connect the voltmeter to the DG Terminal. Its location can be found in the appropriate repair manual.

The ECT terminal can be designated as TT or T1 depending on the vehicle model. The position in the diagnostic check connector remains the same. The voltage will increase in one volt increments from 1 to 8 volts as the throttle is slowly opened. To verify the brake signal, apply the brake pedal while the throttle is wide open. The voltage displayed on the voltmeter screen will go to zero.

If the voltage readings progress in a step-like fashion, it indicates proper operation of the following:

• Throttle sensor • Circuit integrity from the sensor to the ECU • Circuit integrity from the ECU to the diagnostic check connector.



If the voltage remains at 0 volts as the accelerator is depressed, possible causes are:

• Brake signal remains on.

• IDL signal remains on.

• ECU power supply circuit.

• Faulty ECU.

The voltage chart above provides a voltage value for the corresponding throttle opening. This can be used to establish accelerator position for a given throttle opening.



Terminal Voltage and Gear Position To check for shift timing while the vehicle is driven, connect a voltmeter and drive the vehicle. Voltage will increase in one volt increments from 0 to 7 volts. These voltage signals are output from the ECU to indicate a response to system sensors. The lock-up voltages in second and third gear may not be consistently output with throttle opening under 50%. In order to output each voltage signal, the throttle will need to be open greater than 50%. If the gears fail to shift in response to the changes in voltage readings, the solenoids may be sticking or the electrical circuit to the solenoid may have an open.



ECT AnalyzerThe ECT Analyzer is designed to determine if a transmission malfunction is ECU/electrical circuit related or in the transmission. The analyzer is connected at the solenoid electrical connector using appropriate adapter harnesses. The vehicle is driven using the analyzer to shift the transmission.

If the transmission operates properly with the ECT Analyzer, the fault lies between the solenoid connectors up to and including the ECU. On the other hand, if the transmission does not operate properly with the analyzer, the fault is likely to be in the transmission. This would include a failure of the solenoid or a mechanical failure of the transmission. A solenoid may test out electrically and fail mechanically because the valve sticks. Apply air pressure to the solenoid; air should escape when the solenoid is energized and should not escape when the solenoid is not energized.

Operating InstructionsTwo technicians are required when testing with the ECT Analyzer. One technician must actually drive the vehicle, and the second technician will change gears.

CAUTIONThe analyzer leads should be routed away from hot or moving engine components to avoid damage to the tester.

Choose a safe test area where there are no pedestrians, traffic and obstructions.



Testing for proper gear shifting:

1. The driver and passengers should wear seat belts.

2. Depress the service brake pedal.

3. Start the engine and move the vehicle gear selector to Drive.

4. Rotate the gear selector knob on the ECT Analyzer to the "1-2" position. The transmission will shift to second gear.

5. Press and hold the first gear button. The transmission will shift to first gear.

6. Release the parking brake.

7. Accelerate to 10 mph.

8. Release the first gear button. The transmission should shift to second gear.


10. Rotate the selector knob to the number "T' position. The transmission should shift into third gear.


12. Rotate the selector knob to the number "4" position. The transmission should shift to fourth gear.

13. Release the accelerator and coast.

14. Rotate the selector knob to the number "T' position. The transmission should downshift into third gear.

15. Apply the brakes, and stop the vehicle. Testing is complete.

Testing for lockup operation:

1. Operate the vehicle and ECT Analyzer up to fourth gear.


3. Press and hold the "Lockup" button to engage the lockup clutch. Observe the tachometer and note a slight reduction in the engine rpm. (Is more noticeable when the vehicle is going up a slight hill due to converter slippage.)

4. Release the "Lockup" button to disengage the lockup clutch.

5. Apply vehicle brakes, and bring the vehicle to a halt. Test is complete.

Note: Testing for lockup can also be performed with the vehicle stopped, but with the engine running, With the gear shift selector in "D," press the "Lockup" button to engage the lockup clutch. With the converter in lockup, the engine idle rpm will drop significantly or stall. If there is no change 'in the engine idle rpm, the lockup function is not operational.



ASSIGNMENT NAME:_______________________________

1. What components replaced governor and throttle pressure signals in an ECT transmission?

2. How may solenoids are used in a current model ECT transmission. Please

state the function (control) of each?

3. Explain the procedure of how to pull and read a transmission trouble code?

4. Explain the procedure of how to separate between a mechanical and/or an electrical problem in an ECT transmission.

5. How many speed sensors are used on a vehicle with an ECT transmission, state location, correct I.D. (name) of each sensor, and which is the primary input to the ECT computer.

6. Explain the procedure for checking ECT speed sensors.

7. Explain the construction and operation of the ECT speed senor.

8. List all inputs used by the ECT computer and the need for each?

9. Explain the construction and operation of the direct TPS (linear) in relationship to an indirect TPS in an ECT transmission?

10.Explain which ECT diagnostic checks can be made from the Diagnostic connector?

11.Explain the conditions that must occur in order for converter lockup to occur in an ECT transmission.

12.Explain the relationship that the brake switch, cruise control, and coolant temperature sensor (THW) have in common with torque converter lockup.

13.Explain how solenoids can be checked on the car.



SHIFT INTERLOCK SYSTEMThe shift lock system is designed to ensure the proper operation of the automatic transmission. The driver must depress the brake pedal in order to move the gear selector from Park to any other range. In addition, the ignition key cannot be turned to the Lock position and removed from the ignition switch unless the gear selector is placed in the Park position.

There are three systems available in Toyota models; electrical, electrical/ mechanical and mechanical. We will not cover the application by model but rather by system type. For the specifics on a particular model, consult the repair manual.

SHIFT INTERLOCK SYSTEM


Electrical Shift Lock TypeThe electrical type uses electrical control of the shift lock mechanism, as well as the key lock mechanism.

Shift Lock MechanismThe shift lock mechanism is made up of a number of components as seen in the illustration below.

The shift position switch (shift lock control switch) is used to detect the position of the shift lever. It has two contacts, P1 and P2. When the select lever is in the Park position, P1 is on (closed) and P2 is off (open). In this position, the key can be removed but the select lever is locked in position.

When the select lever is in a position other than Park, P1 is off (open) and P2 is on (closed). In this position, the key cannot be removed.

The grooved pin is part of the normal detent mechanism which requires that the shift lever button be depressed in order to move the gear selector into and out of Park position and also into Manual 2 or Manual Low positions. The shift lock plate is mounted next to the detent plate. In the Park position, the grooved pin fits into the slot at the top of the shift plate. The shift lock plate movement is limited by the plate stopper when the solenoid is not energized.



Shift Lock Override ButtonIn order to move the shift lever out of Park, the ignition switch must be in the Accessory or ON position and the brake pedal must be depressed. When the brake pedal is depressed, the ECU turns on the solenoid, moving the plate stopper and allowing the shift lock plate to move down with the grooved pin.

If the shift lock solenoid becomes inoperative, the shift lever cannot be moved and the vehicle cannot be moved. The shift lock override button can be used to release the plate stopper from the shift lock plate, releasing the shift lever so it can be moved from the Park position.

Shift Lock ECUThe ECU is generally found near the shift select lever. The shift lock system computer controls operation of the key lock solenoid and the shift lock solenoid based on signals from the shift position switch and the stop light switch.



Key Interlock SystemA camshaft is provided at the end of the key cylinder rotor. This camshaft has a cam with the cut-out portion of its stroke from the ACC position to the ON or Start position. The pin of the key lock solenoid protrudes out against the cam when the current is on and is pulled back by the return spring when the current is off.

When the shift lever is shifted to a range other than the P range, current flows from the computer to the key lock solenoid, causing the pin to protrude out. If the key cylinder is turned with the pin in this position, it can be turned to the ACC position but cannot be turned further, due to the pin pushing against the cam. This prevents the key cylinder from being turned to the Lock position.

The current to the key lock solenoid is cut off when the shift lever is shifted to the P range and the pin is pulled back by the return spring. This allows the key cylinder to be turned to the Lock position, and the key can be removed.

Shift Lock System ComputerThe shift lock system computer controls operation of the key lock solenoid and the shift lock solenoid based on signals from the shift position switch and the stop fight switch.

Key Lock Solenoid ControlThe shift position switch P2 is on (closed) when the shift lever is in a range other than the Park range. Current from the ACC and ON terminals of the ignition switch flows to Tr2 through the timer circuit. The base circuit of Tr2 is grounded by switch P2, and Tr2 goes on, energizing the key lock solenoid, preventing the key from going to the Lock position. The timer circuit cuts off the flow of current to Tr2 approximately one hour after the ignition switch is turned from ON to ACC, switching off the key lock solenoid. The timer circuit prevents the battery from being discharged.

By placing the gear selector in the Park position, switch P2 is off (open), current no longer flows to the base of Tr2 and it goes off. The solenoid is no longer energized, and the solenoid plunger is retracted, and the key can be removed.



Shift Lock Solenoid ControlWhen the shift lever is in the Park range, shift position switch P1 is on and the emitter circuit of Tr3 is grounded. Base current for Tr3 is provided through the stop light switch which is open while the brake is not applied, so Tr3 is off. Tr3 controls the base of Tr1, and as long as Tr3 is off, the shift lock solenoid will remain off and the gear selector will be locked in the Park position.

When the brake pedal is depressed, the stop light switch goes on, providing current to the base of Tr3. When Tr3 goes on, base current flows in Tr1 and it then goes on, causing current to flow to the shift lock solenoid and freeing the shift lever. When the shift lever is shifted out of Park, the shift position switch P1 goes off and Tr1 switches the shift lock solenoid off.



Electrical / Mechanical Shift Lock TypeThe electrical/mechanical type uses electrical control of the shift lock mechanism and a mechanical control of the key lock mechanism.

Key Interlock DeviceSimilar to the construction discussed previously, a camshaft is provided at the end of the key cylinder rotor. This camshaft has a cam with the cut-out portion of its stroke from the ACC position to the ON or Start position. The lock pin is attached to the end of the parking lock cable and slides with the movement of the control lever mounted to the shift lever mechanism. The control lever is separate from the shift lock plate but is actuated by it.

Notice the crank ditch sloth in the shift lock plate. It is cut at an angle so that when the shift lock plate moves up or down, it causes the control lever to pivot at point B in the illustration below.

When the shift lever is in the Park position, the control lever rotates around B counterclockwise, pushing the parking lock cable so that the lock pin does not interfere with the camshaft. In this position, the key can be turned to the Lock position and removed.

When the shift lever is moved from the Park position, the lock plate is pushed downward by the shift lever button and the grooved pin. When the shift lock plate moves downward the control lever rotates clockwise, pulling the parking lock cable and lock pin into engagement with the camshaft. In this position, the key cannot be turned to the Lock position and removed from the ignition as seen in the following illustration.



Mechanical Shift Lock TypeThe mechanical type uses mechanical control of the shift lock mechanism and the key lock mechanism. A cable extends from the brake pedal bracket to the shift lever control shaft bracket. A lock pin engages the shift lever shaft to lock in into the Park position until the brakes are applied.

The cable (wire) end on the brake pedal bracket is mounted just below the stop light switch. The plunger is attached to the cable and is mounted in a wire guide and is able to slide in and out. When the brake pedal is not depressed, the plunger is held in position by the brake pedal return spring.

The other end of the cable is attached to a lock pin located in the shift lever control shaft bracket. The lock pin is spring loaded to release the lock pin from the inner shaft of the shift lever.



When the shift lever is in the Park range and brakes are not applied, the cable compresses the No. 1 return spring and pushes the lock pin engaging the round hole in the inner shaft, locking the shift lever in Park

When the brakes are applied with the transmission in Park, the No. 1 spring pushes the cable, lock pin and plunger out toward the brake pedal. With the plunger released, the shift lever can be moved from Park.

When the shift lever is in positions other than Park with the brakes released, the brake pedal return spring pushes the plunger and cable back toward the shift lever control shaft. The lock pin cannot enter the inner shaft, so the No. 2 return spring compresses. With the lock pin spring loaded, when the gear selector is moved to the Park position, it will immediately lock.

Reprinted with permission by Toyota Motor Sales, USA, Inc.,from the Automatic Transmission Course #262 textbook.



Electronic Fuel Injection Overview

How Electronic Fuel Injection Works

Electronic Fuel injection works on the some very basic principles. The following discussion broadly outlines how a basic or Convention Electronic Fuel Injection (EFI) system operates.

The Electronic Fuel Injection system can be divided into three: basic sub-systems. These are the fuel delivery system, air induction system, and the electronic control system.

EFI #1 - SYSTEM OVERVIEW


The Fuel Delivery System

• The fuel delivery system consists of the fuel tank, fuel pump, fuel filter, fuel delivery pipe (fuel rail), fuel injector, fuel pressure regulator, and fuel return pipe.

• Fuel is delivered from the tank to the injector by means of an electric fuel pump. The pump is typically located in or near the fuel tank. Contaminants are filtered out by a high capacity in line fuel filter.

• Fuel is maintained at a constant pressure by means of a fuel pressure regulator. Any fuel which is not delivered to the intake manifold by the injector is returned to the tank through a fuel return pipe.



The Air Induction System

• The air induction system consists of the air cleaner, air flow meter, throttle valve, air intake chamber, intake manifold runner, and intake valve.

• When the throttle valve is opened, air flows through the air cleaner, through the air flow meter (on L type systems), past the throttle valve, and through a well tuned intake manifold runner to the intake valve.

• Air delivered to the engine is a function of driver demand. As the throttle valve is opened further, more air is allowed to enter the engine cylinders.

• Toyota engines use two different methods to measure intake air volume. The L type EFI system measures air flow directly by using an air flow meter. The D type EFI system measures air flow indirectly by monitoring the pressure in the intake manifold.



Electronic Control System

• The electronic control system consists of various engine sensors, Electronic Control Unit (ECU), fuel injector assemblies, and related wiring.

• The ECU determines precisely how much fuel needs to be delivered by the injector by monitoring the engine sensors.

• The ECU turns the injectors on for a precise amount of time, referred to as injection pulse width or injection duration, to deliver the proper air/fuel ratio to the engine.



Basic System Operation

• Air enters the engine through the air induction system where it is measured by the air flow meter. As the air flows into the cylinder, fuel is mixed into the air by the fuel injector.

• Fuel injectors are arranged in the intake manifold behind each intake valve. The injectors are electrical solenoids which are operated by the ECU.

• The ECU pulses the injector by switching the injector ground circuit on and off.

• When the injector is turned on, it opens, spraying atomized fuel at the back side of the intake valve.

• As fuel is sprayed into the intake airstream, it mixes with the incoming air and vaporizes due to the low pressures in the intake manifold. The ECU signals the injector to deliver just enough fuel to achieve an ideal air/fuel ratio of 14.7:1, often referred to as stoichiometry.

• The precise amount of fuel delivered to the engine is a function of ECU control.

• The ECU determines the basic injection quantity based upon measured intake air volume and engine rpm.

• Depending on engine operating conditions, injection quantity will vary. The ECU monitors variables such as coolant temperature, engine speed, throttle angle, and exhaust oxygen content and makes injection corrections which determine final injection quantity.



Advantages of EFI

Uniform Air/Fuel Mixture DistributionEach cylinder has its own injector which delivers fuel directly to the intake valve. This eliminates the need for fuel to travel through the intake manifold, improving cylinder to cylinder distribution.

Highly Accurate Air/Fuel Ratio Control Throughout All Engine Operating Conditions EFI supplies a continuously accurate air/fuel ratio to the engine no matter what operating conditions are encountered. This provides better driveability, fuel economy, and emissions control.

Superior Throttle Response and PowerBy delivering fuel directly at the back of the intake valve, the intake manifold design can be optimized to improve air velocity at the intake valve. This improves torque and throttle response.

Excellent Fuel Economy WithImproved Emissions ControlCold engine and wide open throttle enrichment can be reduced with an EFI engine because fuel puddling in the intake manifold is not a problem. This results in better overall fuel economy and improved emissions control.

Improved Cold Engine Startability and Operation The combination of better fuel atomization and injection directly at the intake valve improves ability to start and run a cold engine.

Simpler Mechanics, Reduced Adjustment Sensitivity The EFI system does not rely on any major adjustments for cold enrichment or fuel metering. Because the system is mechanically simple, maintenance requirements are reduced.



EFI/TCCS System

With the introduction of the Toyota Computer Control System (TCCS), the EFI system went from a simple fuel control system to a fully integrated engine and emissions management system. Although the fuel delivery system operates the same as Conventional EFI, the

Ignition Spark Management (ESA)The EFI/'TCCS system regulates spark advance angle by monitoring engine operating conditions, calculating the optimum spark timing, and firing the spark plug at the appropriate time.

Idle Speed Control (ISC)The EFI/TCCS system regulates engine idle speed by means of several different types of ECU controlled devices. The ECU monitors engine operating conditions to determine which idle speed strategy to use.

TCCS Electronic Control Unit (ECU) also controls ignition spark angle. Additionally, TCCS also regulates an Idle Speed Control device, an Exhaust Gas Recirculation (EGR) Vacuum Switching Valve and, depending on application, other engine related systems.

Exhaust Gas Recirculation (EGR)The EFI/TCCS system regulates the periods under which EGR can be introduced to the engine. This control is accomplished through the use of an EGR Vacuum Switching Valve.

Other Engine Related SystemsIn addition to the major systems just described, the TCCS ECU often operates an Electronically Controlled Transmission (ECT), a Variable Induction System (T-VIS), the air conditioner compressor clutch, and the turbocharger/supercharger.



Self Diagnosis System

A self diagnosis system is incorporated into all TCCS Electronic Control Units (ECUs) and into some Conventional EFI system ECUs. A Conventional EFI engine equipped with self diagnostics is a P7/EFI system. This diagnostic system uses a check engine warning lamp in the combination meter which is capable of warning the driver when specific faults are detected in the engine control system. The check engine light is also capable of flashing a series of diagnosis codes to assist the technician in troubleshooting these faults.

Summary

The Electronic Fuel Injection system consists of three basic subsystems.

• The electronic control system determines basic injection quantity based upon electrical signals from the air flow meter and engine rpm.

• The fuel delivery system maintains a constant fuel pressure on the injector. This allows the ECU to control the fuel injection duration and deliver the appropriate amount of fuel for engine operating conditions.

• The air induction system delivers air to the engine based on driver demand. The air/fuel mixture is formed in the intake manifold as air moves through the intake runners.

The EFI system allows for improved engine performance, better fuel economy, and improved emissions control. Although technologically advanced, the EFI system is mechanically simpler than other fuel metering systems and requires very little maintenance or periodic adjustment.

• The Conventional EFI system only controls fuel delivery and injection quantity. 'Me introduction of EFI/TCCS added control Of Electronic Spark Advance, idle speed, EGR, and other related engine systems.

• Most of Toyota's late model EFI systems are equipped with some type of on board diagnosis system. All TCCS systems are equipped with an advanced self diagnosis system capable of monitoring many important engine electrical circuits. Only some of the later production Conventional(P7) EFI engines are equipped with a self diagnosis system.

Reprinted with permission from Toyota Motor Sale, U.S.A., Inc. from #850 EFI Course Book.



Overview Of TheAir Induction System

The purpose of the air induction system is to filter, meter, and measure intake air flow into the engine. Air, filtered by the air cleaner, passes into the intake manifold in varying volumes. The amount of air entering the engine is a function of throttle valve opening angle and engine rpm. Air velocity is increased as it passes through the long, narrow intake manifold runners, resulting in improved engine volumetric efficiency.

Intake air volume is measured by movement of the air flow meter measuring plate or by detecting vortex frequency on engines equipped

with L type EFI. On engines equipped with D type EFI, air volume is measured by monitoring the pressure in the intake manifold, a value which varies proportionally with the volume of air entering the engine.

The throttle valve directly controls the volume of air which enters the engine based on driver demand. Additionally, when the engine is cold, it is necessary for supplementary air to by-pass the closed throttle valve to provide cold fast idle. This is accomplished by a bi-metallic or wax type air valve or by an ECU controlled Idle Speed Control Valve (ISCV).

EFI #2 - AIR INDUCTION SYSTEM


Air InductionSystem Components

Vane Air Flow Meter (L Type EFI) The vane type air flow meter is a commonly used air volume measurement device on Toyota EFI engines. The meter consists of a measuring plate, which is spring loaded closed by a return spring, and a potentiometer attached to the plate, which varies an electrical signal to the ECU as the position of the plate changes. Air volume entering the engine is directly proportional to the amount of movement detected from the measuring plate. Additionally, the air flow meter incorporates a fuel pump enable contact which breaks the ground circuit of the circuit opening relay if the engine stops running.

The air flow meter is placed in series between the air cleaner and the throttle body, thereby measuring all air which enters the engine. Integrated with the air flow meter is an intake air temperature sensor and an idle mixture by-pass passage.

Idle Mixture Air By-pass Circuit For proper calibration of the engine air/fuel ratio at idle speed, an idle mixture air by-pass circuit is incorporated into the air flow meter. A screw is used to adjust the amount of air which by-passes the measuring plate. This screw is adjusted and sealed at the factory to discourage improper adjustment and tampering. There are no provisions or specifications for field adjustment.

After factory calibration of the air flow meter, a two-digit number is stamped into the meter casting near the idle mixture adjusting screw. This number indicates the distance from the casting to the flat surface of the screw and can be used as a reference if the idle mixture screw has been tampered with.

The calibration number can be interpreted by referring to the examples in the following chart.



Fuel Pump Circuit ControlA fuel pump switch is incorporated into the air flow meter to prevent the fuel pump from running unless the engine is running. Any movement of the air flow meter measuring plate will cause the fuel pump switch contact to close. When the engine is not running, the measuring plate forces the fuel pump switch contact open, preventing the circuit opening relay from operating. For more information on the fuel pump electrical circuit, refer to section 3, "Fuel Delivery and Injection Control."

Karman Vortex Air Flow Meter(L Type EFI)The Karman vortex air flow meter is used only on limited applications (7M-GTE and Lexus 1UZ-FE & 2JZ-GE engines). The meter is smaller and lighter than the vane type meter and offers less resistance to incoming air flow.

The sensor operates on the principle of measuring the vortices created as air flows past a pillar shaped vortex generator. The frequency with which these vortices are created increases in direct proportion to the amount of air flowing across the vortex generator. Vortex frequency is detected by a photocoupler and converted into a variable frequency digital signal by the sensor. An intake air temperature sensor is also incorporated into the Karman vortex air flow meter. For more information about operation of this air flow meter and its signals , refer to section 5, "Electronic Engine Controls."

Throttle Body The throttle body consists of the throttle valve, the idle air by-pass circuit, the throttle position sensor, and also houses various ported and manifold vacuum sources to operate emissions devices. Throttle icing is prevented by use of an engine coolant cavity located adjacent to the throttle valve.



Idle Air By-passDuring idle operation, the throttle valve is almost completely closed. Idle air enters the engine through an adjustable throttle air by-pass screw which varies the amount of air which can flow past the closed throttle valve. By turning this screw clockwise, throttle bypass air is reduced, causing a decrease in idle speed. Conversely, turning the screw counterclockwise will increase idle speed by allowing more air to pass the closed throttle valve.

On engines equipped with an ECU controlled ISCV, this throttle air by-pass screw is seated at the factory, and there are no provisions for curb idle adjustment. Idle air is varied by the ECU through control of the ISC Valve position.

Decel Dashpot and ThrottleOpener SystemsA decel dashpot or throttle opener is mounted to the throttle body on some engines. The decel dashpot is designed to keep the throttle valve from closing too suddenly during deceleration. The throttle opener is designed to hold the throttle valve open slightly after the engine is turned off.

Non ECU Controlled Throttle OpenerStarting with 1990 3S-FE and 5S-FE engines, a simple throttle opener diaphragm was added to the throttle body. The throttle opener diaphragm is spring loaded in the extended position, holding the throttle valve open slightly when vacuum is not applied to the diaphragm. When the engine is started, manifold vacuum from the TO port retracts the throttle opener for normal curb idle.

The intent of the throttle opener system is to keep the throttle valve slightly open after the engine is turned off.

Non-ECU Controlled Dashpot On some engines, a simple dashpot is used. When the throttle is open, the dashpot diaphragm spring extends the control rod, allowing atmospheric pressure to enter the diaphragm chamber through a small bleed restriction (VTV).



When the throttle closes, the throttle return spring pushes the dashpot control rod toward the retracted position. Atmospheric pressure trapped in the diaphragm chamber slowly bleeds through the restriction, causing the throttle to close slowly.

ECU Controlled CombinationThrottle Opener/DashpotDashpot and throttle opener functions are combined into one ECU controlled system on some late model engines like the '91 3E-E. This system uses an ECU controlled VSV to switch vacuum to the throttle opener/dashpot diaphragm.

• When the engine is stopped, spring tension extends the control rod, causing the throttle to open.

• When the engine is running above a given rpm, the ECU energizes the VSV, allowing atmospheric pressure to bleed into the throttle opener/dashpot diaphragm through the Vacuum Transmitting Valve (VTV). This allows spring tension to extend the control rod.

• When the throttle angle closes beyond a specified point during deceleration, the ECU de-energizes the VSV, allowing manifold vacuum to bleed through the VTV and act on the diaphragm. This causes the control rod to gradually retract, slowly closing the throttle valve.

The idle air by-pass screw, dashpot, and throttle opener do not require routine adjustment. In the event that these components have been tampered with, refer to the appropriate repair manual for adjustment procedures of curb idle, dashpot, throttle opener, and A/C idle up.

• ECU turns VSV ON as throttle opens; rod extends

• ECU turns VSV OFF on deceleration; rod allows throttle to close slowly

• Engine OFF; rod extends, holding throttle open slightly



Air ValvesThere are two types of non-ECU controlled air valves used on some engines to control cold engine fast idle. These valves, the electrically heated bi-metal type and the coolant heated wax type, vary the amount of air bypassing the closed throttle valve during cold engine operation.

Bi-metal Type Air ValveThis gate valve operates on the principle of a spring loaded gate balanced against a bi-metal element. The tension of the bi-metallic element varies the position of the gate as its temperature changes. The bi-metal element is heated by an electrical heater coil and by the temperature of the ambient air surrounding it. The air valve assembly is installed on the surface of the cylinder head to keep the gate valve closed during hot soak periods.



Heater current for the air valve is supplied by the circuit opening relay power contact, the same circuit which feeds the fuel pump.

Air valve operation can be quick checked by pinching off a supply hose and observing the rpm drop. When checked with a warm engine, the drop should be less than 50 rpm. When the engine is cold, the rpm drop should be high.



Wax Type Air ValveThe wax type air valve is integrated with the throttle body and varies an idle air by-pass opening as coolant temperature changes. The valve works on the principle of a spring loaded gate valve balanced against a coolant heated, wax filled thermo valve.

When coolant temperature is cold, the wax filled thermo valve retracts allowing spring A to push the gate valve open. This allows air to flow from the air cleaner side of the valve to the intake side of the valve.

As coolant temperature rises, the wax filled thermo valve expands allowing spring B to gradually close the valve (spring B is stronger than spring A). This causes engine rpm to decrease as air flow to the intake is decreased.

The wax type air valve should be fully closed by the time engine coolant temperature reaches approximately 80'C (176'F).

• Cold engine, large rpm drop• Fully warmed engine!~100 rpm drop



A good quick check for the wax type air valve is to observe engine rpm throughout the warm up cycle. Look for high rpm upon initial startup and gradual reduction to normal curb idle speed as the engine reaches normal operating temperature.

On D type EFI, the valve operation can also be checked by removing the air inlet pipe at the throttle body and blocking the fresh air port inside the throttle bore. When the engine is cold, engine rpm should drop greater than 100 rpm. Once the engine reaches normal operating temperature (~~ 176'F), rpm drop should not exceed 100 rpm.

Intake Air Chamber & ManifoldPort delivered Electronic Fuel Injection systems offer the advantage of not having to move fuel through the intake manifold. This allows for improved performance and emissions through optimum design of the intake air chamber and manifolds.

A large intake air chamber is provided to eliminate pulsation, thereby improving air distribution to each manifold runner. Long, narrow manifold runners are branched off to each intake port to improve air velocity at the intake valve. This design offers the following benefits:

• Fuel puddling is eliminated, providing for leaner cold engine and power air/fuel ratios. This equates to reductions in emissions and improved fuel economy.

• Volumetric efficiency of the engine is improved, thereby improving engine torque and horsepower.

Depending upon application, the intake air chamber and manifolds may be integrated or separate. Some Toyota engines utilize an ECU controlled variable induction system which optimizes manifold design for low and high speed engine operation. For more information on these systems, refer to "Other TCCS Related Systems."



Manifold Absolute PressureSensor (D Type EFI)The D type EFI system eliminates the use of an air flow meter and uses a manifold absolute pressure sensor as a load measurement device instead.

Because pressure in the intake manifold is proportional to the amount of air entering it, the manifold absolute pressure sensor is used to measure air intake volume in the D type EFI system.

This sensor compares a variable pressure inside the intake manifold with a fixed reference pressure inside the sensor. A total vacuum chamber is placed on one side of a piezo-resistive silicon chip; manifold pressure is applied to the other side of the chip. As the chip flexes, the mechanical movement is converted into a variable voltage signal by the sensor. There are several different names used in reference to the Manifold Absolute Pressure sensor, depending on the publication you read. Two other common names used to refer to this sensor are PIM, or Pressure Intake Manifold, and Vacuum sensor.

For more information about operation of the manifold absolute pressure sensor and its signal characteristics, refer to "Electronic Engine Controls."



Idle-Up Systems

Air Conditioning Idle-upThe air conditioning idle-up system is used to increase engine idle rpm any time the air conditioning compressor is in operation. The system shown is used on D type EFI applications where the ECU controlled Idle Speed Control Valve (ISCV) does not have an A/C idle-up feature. This system maintains engine idle stability during periods of A/C compressor operation. Additionally, it keeps compressor speed sufficiently high to ensure adequate cooling capacity at idle speed.

The A/C idle-up system consists of an A/C amplifier controlled Vacuum Switching Valve (VSV) and an Air Switching Valve (ASV) or actuator. By applying vacuum to the ASV diaphragm, fresh air from the air cleaner is by-passed into the intake manifold, increasing engine rpm.

When the VSV is energized, a manifold vacuum signal is applied to the actuator diaphragm of the ASV causing it to open the passage between the fresh air supply and the intake manifold. This extra air introduced directly into the intake manifold causes engine rpm to increase.

When the VSV is de-energized, the vacuum control signal to the ASV is blocked and any trapped vacuum is bled off of the diaphragm. This causes the ASV to block air flowing to the intake manifold, decreasing rpm.

The A/C idle-up system described above is not an ECU controlled system. For information on ECU controlled ISCV systems which control A/C idle-up speed, refer to "Engine Controls - Idle Speed Control Systems."



Power Steering Idle-upThe power steering system draws a significant amount of horsepower from the engine when the steering wheel is turned to either stop. This can have an adverse effect on vehicle driveability. To address this potential problem, many EFI engines equipped with power steering use a power steering idle-up system which activates whenever the steering wheel is turned to a stop.

The power steering idle-up system consists of a hydraulically operated air control valve and a vacuum circuit which by-passes the throttle valve. Whenever power steering pressure exceeds the calibration point of the control valve, the valve opens, allowing a calibrated volume of air to by-pass the closed throttle valve.

Because power steering pressure only exceeds the pressure calibration point of the valve when the steering wheel is turned to its stop, the system is only functional during very low speed maneuvering and at idle. The system can be tested by turning the steering wheel to a stop while listening for an rpm increase.



Common ServiceConcerns and Solutions

During service procedures, there are two concerns related to the air induction system which the technician should be aware of. These are false or unmeasured air entry into the intake system and deposit buildup on the back side of intake valves.

False air is any air which enters the induction system unwanted and/or unmeasured. In addition to obvious leaks in the intake manifold, with an L type EFI system, false air can enter the induction system through the connecting pipe between the air flow meter and the throttle body as well as through leaks into the crankcase. Because this air is able to enter the intake manifold unmeasured, the result is an excessively lean air/fuel ratio. The end result of false air with L type EFI is rough idle, stumble, and/or flat spots.

With the D type EFI system, false air is typically measured by the EFI system because it results in an increase in manifold absolute pressure. The end result is an engine that idles excessively high but with a relatively normal air/fuel mixture.

There are several tests which can detect false air entry into the induction system. A good visual inspection of the intake air connector pipe and connection points as well as inspection of all vacuum hoses, engine oil filler cap, and dip stick seals are a must.

If this fails to identify a suspected leak, spraying carburetor cleaner around suspected leak areas while observing an infrared exhaust analyzer for carbon monoxide increase is another method to assist in leak detection.

Another method to locate suspected false air entry points is to pressurize the intake system with a regulated shop air supply (CAUTION: do not exceed 25 PSI). Spray a soapy water solution around all suspected leak areas. Simply listen and observe for bubbles to locate leak sources. This method requires sealing the air cleaner fresh air inlet and blocking the throttle valve open to pressurize the intake air connector pipe. The air pressure can be applied through any large manifold vacuum fitting.



This condition manifests itself as hardened carbon deposits on the back side of the intake valves. It varies in degree depending on the engine, fuel quality, and customer driving habits.

Intake valve deposits present a dual problem. First, these deposits restrict the flow of air and fuel mixture into the cylinder, reducing volumetric efficiency and potentially affecting high rpm engine performance. Additionally, these carbon deposits act like sponges absorbing fuel vapor. This causes lean driveability problems, particularly during cold engine operation.

The best way to identify this condition is by symptom and then through visual inspection. A visual inspection can be performed using a borescope, SSI #00451-42889, to confirm the problem. The intake manifold can also be removed to confirm the existence and the degree of this condition.

The accompanying chart will help you to determine the appropriate action to take based upon visual inspection. Visual inspection can be performed without removal of the cylinder head or intake manifold by using a borescope, SSI 00451-42889. The engine can be manually rotated until the intake valve is fully open; then the borescope

can be inserted through a spark plug hole for inspection.

Repairs can be affected by use of SST 00002216401, a walnut shell type Carbon Cleaner Kit, and 00002-217256, a Universal Plate & Gasket Kit. These tools will allow removal of deposits without removal of the cylinder head.

Summary In this chapter, you have learned that the air induction system filters, meters, and measures air flow into the engine. By using multiple port injection, the intake system can be designed with long tuned intake runners to improve the engine's volumetric efficiency.

Air flow into the engine is controlled by the driver by opening and closing the throttle valve. As air enters the engine, it is measured by one of three different types of air flow meters with L type injection or by a manifold absolute pressure sensor with D type injection.

To improve engine idle quality during cold engine operation, some engines use a mechanical air valve to control air flow past the closed throttle valve. There are two different types of air valves used, one heated by engine coolant, the other heated electrically.

Depending on engine application, there are several different types of throttle control and idle-up devices used. Throttle body mounted devices provide a deceleration dashpot function and/or throttle opener function. Remotely mounted idle-up devices are used on some engines to control additional air flow into the engine when load from the A/C compressor or power steering pump are placed on the engine.

In section 3, Fuel Deliver & Injection controls, you will learn about the fuel delivery system.



Overview of theFuel Delivery SystemThe fuel delivery system incorporates thefollowing components:

1) Fuel tank (with evaporative emissionscontrols)

2) Fuel pump3) Fuel pipe and in line filter4) Fuel delivery pipe (fuel rail)5) Pulsation damper (many engines)6) Fuel injectors7) Cold start injector (most engines)8) Fuel pressure regulator9) Fuel return pipe

Fuel is pumped from the tank by an electric fuel pump, which is controlled by the circuit opening relay. Fuel flows through the fuel filter to the fuel rail (fuel delivery pipe) and up to the pressure regulator where it is held under pressure. The pressure regulator maintains fuel pressure in the rail at a specified value above intake manifold pressure. This maintains a constant

pressure drop across the fuel injectors regardless of engine load. Fuel in excess of that consumed by engine operation is returned to the tank by way of the fuel return line. A pulsation damper, mounted to the fuel rail, is used on some engines to absorb pressure variations in the fuel rail due to injectors opening and closing.

The fuel injectors, which directly control fuel metering to the intake manifold, are pulsed by the ECU. The ECU completes the injector ground circuit for a calculated amount of time referred to as injection duration or injection pulse width. The ECU determines which air/fuel ratio the engine runs at based upon engine conditions monitored by input sensors and a program stored in its memory.

During cold engine starting, many engines incorporate a cold start injector designed to improve startability below a specified coolant temperature.

EFI #3 - FUEL DELIVERY & INJECTION CONTROL


Fuel Delivery andInjection Control Components

Fuel PumpsOver the years, Toyota has used two types of electric fuel pumps on EFI systems. The early Conventional EFI system used an externally mounted in-line pump. These roller cell pumps incorporate an integral pressure pulse damper or silencer designed to smooth out pressure pulses and provide quiet operation.



Later model production engines utilize an in-tank pump integrated with the fuel sender unit. These turbine pumps operate with less discharge pulsation and run quieter than the in-line variety. In-tank pumps can be serviced by removing the fuel sender unit from the tank. Make sure that the pump coupling hose is in good condition prior to replacing the pump.

Both pumps share many features. They are referred to as wet pumps because the electric motor operates immersed in fuel. Passing fuel through the pump motor aids in cooling and lubrication.

An outlet check valve is incorporated in the discharge outlet to maintain residual or rest pressure when the engine is turned off. This reduces the possibility of vapor-lock and improves starting characteristics. A pressure relief valve is used to prevent over-pressure and potential fuel leakage in the event that pressure or return lines become restricted.



Fuel Pump Electrical Controlsand Circuit Opening Relay

Circuit Opening Relay Circuits There are three types of fuel pump control circuits used on Toyota's EFI engines. One type of control,

A second type of fuel pump control uses the ECU to control circuit opening relay run winding current. Used on engines equipped with D type EFI and on the 7M-GTE, which uses a Karman vortex air flow meter, this

used exclusively with L type injection, utilizes the air flow meter Fc contact to complete the circuit opening relay run winding ground. This is a safety feature which prevents the fuel pump from operating when the engine is not running.

safety feature prevents fuel pump operation whenever the ECU fails to see an Ne (engine rpm) signal. Under these conditions, the ECU removes ground from the circuit opening relay run winding.



Fuel Pump Speed ControlThe third type of fuel pump control circuit utilizes a two-speed pump electrical circuit. Depending upon engine, the circuit opening relay may be driven by the ECU or by the air flow meter Fc contact. Pump current, however, is supplied either through a current limiting resistor or directly to the pump depending on engine load, rpm and status of the STA signal.

When the engine is cranked, or operated at high speed and/or heavy load, the ECU turns off TR1, closing contact A of the Fuel Pump

Control Relay. This allows current to flow directly to the fuel pump, causing it to run at high speed.

Under all other operating conditions, the ECU turns on TR1, which energizes the Fuel Pump Control Relay. This closes relay contact B and forces current to flow through the resistor, causing the pump to run at low speed. The Fuel Pump Speed Control system is designed to reduce electrical demand and pump wear when fuel demand is low while delivering adequate fuel volume when demand is high.



Fuel Pump Test TerminalsTo facilitate testing and allow pump operation independent of the air flow meter or ECU control, all engines utilize a fuel pump test connector.

There are two basic types of fuel pump test circuits. Most late model TCCS engines use an Fp test terminal located in the check connector. With the ignition switch on,

jumpering +B to the Fp terminal sends current-directly to the fuel pump.

Earlier engines use a jumper connector referred to as a 2P fuel pump check connector. This connector, when jumpered, supplies ground for the circuit opening relay run winding, allowing it to operate independently of the air flow meter Fc contact.



Fuel Filter

The fuel filter, which is installed between the pump and the fuel rail, removes dirt and contaminants from the fuel before it is delivered to the injectors and pressure regulator.

Although it is possible for the fuel filter to become contaminated or even completely clogged, this is an unlikely condition because of the high capacity and quality of Toyota's filter. This filter is considered to be maintenance free and no service interval is recommended for periodic replacement.

In the event that this filter becomes restrictive to fuel flow, the engine will suffer from surging, loss of power under load and hard starting problems. If it becomes necessary to replace this filter there are some important safety matters to consider.

Fuel Delivery Pipe (Fuel Rail)The fuel delivery pipe, commonly referred to as a fuel rail, is designed to hold the injector in place on the intake manifold. Mounted to the fuel delivery pipe are the pulsation damper (when used) and the fuel pressure regulator. The fuel delivery pipe acts as a reservoir for fuel which is held under pressure prior to delivery by the fuel injector.



Fuel Pressure RegulatorThe fuel pressure regulator is a diaphragm operated pressure relief valve. To maintain precise fuel metering, the fuel pressure regulator maintains a constant pressure differential across the fuel injector. This means that the pressure in the fuel rail will always be at a constant value above manifold absolute pressure.

The specified pressure differential is either 36 PSI (2.55 kg/CM2) or 41 PSI (2.90 kg/CM2) depending on engine application.* Maintenance of this pressure differential is accomplished by balancing a spring, assisted by manifold pressure, against a diaphragm which holds a ball valve on its seat.

Pulsation DamperAlthough fuel pressure is maintained at a constant value by the pressure regulator, the pulsing of the injectors causes minor fluctuations in rail pressure. The pulsation damper acts as an accumulator to smooth out these pulsations, ensuring accurate fuel metering.

The fuel pulsation damper is not used on all engines but can be used as a fuel pressure quick check on those engines which it is used. Noting the diaphragm, when pressure is present, the bolt head in the center of the diaphragm extends out flush with the top of the damper case.



Fuel Pressure Up SystemThe fuel pressure up system (FPU) is designed to reduce the possibility of vapor formation in the fuel rail after hot soak and is used on many TCCS engines. It utilizes an ECU controlled Vacuum Switching Valve (VSV) to open an atmospheric bleed into the manifold reference line to the fuel pressure regulator.

This solenoid is energized during hot engine cranking and for up to two minutes after the engine starts. The ECU grounds the FPU

VSV based on input received from STA and THW signals. Energizing the solenoid bleeds atmospheric pressure into the fuel pressure regulator vacuum chamber increasing fuel rail pressure to its maximum level.

On some engines, the ECU also monitors engine load and rpm signals (Vs, PIM and Ne) and energizes the VSV under heavy load and high rpm operation to ensure maximum fuel rail pressure.



Fuel Pressure and Volume TestingSafety Tips: Prior to installing a fuel pressure gauge and checking fuel pressure, residual pressure must be safely relieved to reduce the hazard of fire when the fuel line is opened. It is advisable to have a fire extinguisher whenever opening the fuel system.

Common gauge hookup locations are at the fuel rail, fuel filter, or the cold start valve using SST #09268-45012 and #09268-45013-01. Repair manual procedures should always be followed. Whenever a fuel hose connection secured with a copper sealing gasket is opened, a new gasket should be used when the hose is re-secured after service.

Fuel pressure and volume tests can be divided into six separate areas.

The following tests and specifications are general guidelines; consult the repair manual for actual specifications and procedures.

CAUTION: Perform this test only long enough to determine if pressure rises above minimum specification; risk exists of blowing coupler hose off of pump. This test is only necessary if other pressure tests indicate lower than normal fuel pressure.

Fuel InjectorsThe fuel injector is an electro-mechanical device which meters, atomizes and directs fuel into the intake manifold based on signals from the ECU driver circuit(s). All Toyota engines used in the U.S.A. position the injectors, one per cylinder, directly behind the intake valve. The injectors are installed with an insulator/seal on the manifold end to isolate the injector from heat and to prevent an atmospheric pressure leak into the manifold. The fuel delivery pipe serves to secure the injector in place. Fuel is sealed on the delivery pipe end by an O-ring and grommet.

To reduce the possibility of vapor lock, which tends to occur during high temperature operation, the 3S-GTE and 2TZ-FE engines use a side feed injector. This type of injector seals with an upper and lower O-ring. O-rings and insulators should always be replaced when injectors are removed; they should never be re-used.



Air Assist SystemTo promote better fuel atomization, the 3VZ-FE engine uses an air assist system which meters air from the Idle Speed Control (ISC) valve directly to the nozzle of the fuel injector.

An adaptor for the air assist system is added to a standard two-hole type injector to provide an air distribution gallery. Air is mixed with fuel in the chamber formed by the injector insulator grommet and the lower O-ring.



Types Of Injectors In UseToyota currently uses four different types of fuel injectors depending on engine application. These can be broken down into pintle type and hole type (cone valve and ball valve), high resistance and low resistance.

Pintle Type Injector - This was the original design used on early Conventional and EFI/ TCCS engines. This injector gets its name from the type of valve used to control fuel atomization and flow. It offers good atomization of fuel but is susceptible to deposit buildup on the pintle valve. Deposits cause restriction to fuel flow promoting lean fuel delivery and altered injector spray pattern.

Hole Type Injector - Hole type injectors were introduced on later model EFI/TCCS engines to reduce concerns with injector deposits. The inject.on valve is recessed from the tip of the injector and fuel is delivered through holes drilled in a director plate at the injector tip. The hole type injector offers good fuel

atomization while demonstrating better resistance to deposit buildup compared to the pintle design. There are currently three designs of hole type injectors in use, including a side feed injector used on the 3S-GTE and 2TZ-FE engines.

High And Low Resistance Injector Windings There are two different types of injector coil windings used depending on the type of drive circuit used and whether or not an external resistor is being used.

Low resistance injectors, which typically range between 2 - 3 Ω @ 70'F, are used with an external resistor in a voltage controlled driver circuit. Low resistance injectors are also used without an external resistor in a current controlled driver circuit.

High resistance injectors, which typically run about 13.8 Ω @ 70'F, do not require the use of an external resistor in a voltage controlled driver circuit.



Injector Driver CircuitsCurrent is supplied to the ECU driver circuits (#10 and #20 in example) through the fuel injectors. Current flows either directly from the ignition switch or from the EFI Main Relay. When the ECU driver circuit turns on, current flows to ground through the injector solenoid coil. The magnetic field created causes the injector to open against spring tension. When the ECU driver circuit turns off, the spring closes the injector valve.

There are two common types of driver circuits currently in use on Toyota EFI engines; both of these driver circuits work on the voltage control principle. One uses an external solenoid resistor and a low resistance injector, the other using a high resistance injector without the solenoid resistor. In both cases, the high circuit resistance is required to limit current flow through the injector winding. Without this control of the current flow through the injector, the solenoid coil would overheat, causing injector failure.



A third type of driver circuit was used by Toyota on overseas models using the 4A-GE engine with D type EFI. Referred to as a current controlled driver circuit, it has never been used by Toyota on vehicles sold in the U.S.A. but is widely used by other auto manufacturers. This type of driver circuit uses a low resistance injector and limits current flow by controlling the gain of the driver transistor. The advantage to the current controlled driver circuit is the short time period from when the driver transistor goes on to when the injector actually opens. This is a function of the speed with which current flow reaches its peak.

In terms of injection opening time, the external resistor voltage controlled circuit is somewhat faster than the voltage controlled high resistance injector circuit. The trend, however, seems to be moving toward use of this latter type of circuit due to its lower cost and reliability. The ECU can compensate for slower opening time by increasing injector pulse width accordingly.

Caution: Never apply battery voltage directly across a low resistance injector. This will cause injector damage from solenoid coil overheating. Use the proper SST inspection wire will ensure proper series resistance.



Fuel Injection Patternand Injection Timing

Fuel injectors can be pulsed in one of four patterns depending on application. These injection patterns are:

• Simultaneous

• Two groups of two injectors each (four cylinder engines)

• Three groups of two injectors each (six cylinder engines)

• Independent (sequential)

The following chart represents fuel injection grouping and timing patterns.

Because injection timing is based on engine rpm, the ECU must receive an rpm signal to operate the injector driver circuits. With Conventional EFI, this signal comes directly from the coil and is identified as IG. With TCCS, the rpm and crankshaft position identification signals come from the Ne and G1 sensors located in the distributor. If these signals are lost, the ECU will not pulse the injectors.



Fuel Injection VolumeFuel injection volume determination is based upon the value of input sensor signals. In addition to volume control, the ECU can pulse the injectors either synchronously or non-synchronously with ignition events. Both of these topics will be addressed in Chapter 5, "The Electronic Control System."

Common Service Concerns and Solutions

Injector Maintenance and CleaningAlthough it is not the problem it was back in the early to mid '80s, fuel injector restriction is still an issue which needs to be addressed from both a preventative maintenance and repair viewpoint.

The best method of injector maintenance is continuous use of high quality fuels with a level of detergency adequate to keep the injector nozzles clean. It is also prudent to offer injector cleaning service using the Toyota approved injector cleaning system and solvents. This service can be offered whenever the vehicle is in for major service to maintain good engine performance and reduce the possibility of expensive injector replacement due to nozzle build-up.

It has been established that engines using hole type injectors tend to have fewer problems with fouling than those with pintle type injectors. It has also been established that use of low quality fuels which lack adequate detergent additives can lead to injectors which become flow restrictive or which develop poor spray patterns.

When an injector becomes flow restricted, the volume of fuel delivered for a given injection duration will be reduced. This condition will cause lean driveability problems like stumble, hesitation, backfire and surging, especially during open loop operation.

When an injector develops a poor spray pattern, fuel is not atomized and vaporized properly. It is entirely possible that the correct volume of fuel will be delivered to the intake manifold, however, this fuel will enter the cylinder as liquid droplets and will not burn. This condition will cause increased hydrocarbon emissions and lean driveability problems just as if the fuel delivery were lean. The symptoms of poor spray pattern can be very similar to those of flow restricted injectors.

When it comes time to diagnose these two problems, the recommended procedure is to remove the injectors from the engine and bench flow test each injector using the following tools. This procedure is covered in detail in the appropriate repair manuals.

The following information covers the general test procedure.



Caution: Do not create sparks near fuelInjector and graduated cylinder. Keep fireextinguisher nearby while performing this test.



Fuel Starvation Under Load When troubleshooting performance problems which are related to insufficient fuel delivery, the fuel pickup filter should not be overlooked as one possible source of restriction. Contaminants in fuels can restrict this in tank filter sufficiently to cause engine performance problems. In many cases, the engine will perform normally under light load conditions.

The in-line filter, although considered to be a "lifetime" filter, can also cause fuel starvation under load and hard starting if it becomes restricted.

The best method of diagnosing suspected fuel starvation which takes place under load conditions is road testing with a fuel pressure monitor safely installed on the vehicle.

Injector Installation CautionsIt is very important to use new O-rings and grommets when installing injectors to prevent leakage of fuel and potential air leaks into the manifold. O-rings should be

lubricated with gasoline during installation and injectors should be checked for smooth rotation once installed to ensure proper seating.

Finally, many applications use a bi-directional spray pattern which requires precise positioning of the injector in relation to the cylinder head. Use care to follow proper procedures outlined in the appropriate repair manual.



Injector Placement Placement of injectors by cylinder is not usually necessary; however, starting with the 1991 Tercel 3E-E engine, injectors with two different hole placements are used. The injectors from cylinders number 1 and 3 are not interchangeable with those installed in cylinders number 2 and 4.

Always refer to the appropriate repair manual before installing the injectors on the 3E-E or any other engine as this will ensure correct installation. Failure to properly install and position injectors can cause subtle driveability problems which may be difficult to find after the fact.



Cold Start Injection SystemTo improve engine starting when coolant temperatures are low, a supplementary injector is installed on many EFI engines. The cold start injection system consists of the following components:

1) Cold Start Injector

2) Start Injector Time Switch

3) ECU (most EFI/TCCS)

Cold Start InjectorThe cold start injector is located at some central location in the intake manifold. It is designed to supplement the cranking air/fuel ratio and prime the intake manifold in much the same way as a choke valve does while cranking a carbureted engine.

This injector, controlled by the start injector time switch and ECU, sprays a finely atomized mist of fuel while the engine is cranked to improve the speed with which the engine starts. To prevent engine flooding, the injection time is limited by calibration of the start injector time switch and a timer in the ECU.

Start Injector Time SwitchThe function of the start injector time switch is to control the cold start injector ground circuit and to determine maximum injection duration while cranking. Its bi-metallic switch is heated by both engine coolant and an electrical heater.

When the engine is cranked, current flows from the STA circuit of the ignition switch to the cold start injector. Current also flows to the heater coils of the start injector time switch. When the bi-metallic contact of the start injector time switch is closed, current flows through the STJ circuit to ground, causing the cold start injector to deliver fuel.



As the bi-metallic switch is heated by electric current, it opens, causing the STJ circuit to be broken. This prevents the cold start injector from delivering fuel.

Heater coils 1 and 2 are wired to accommodate heater current flow whether or not the time switch is closed.

When the time switch contact is open, current can still flow through Heat Coil 2, thereby preventing the contact from closing in the middle of a cranking cycle.

ECU Cold Start Injector ControlOn most TCCS engines, an alternate ground may be supplied to the cold start injector by the ECU at the STJ terminal. Based on signals from the coolant temperature sensor, the ECU can operate the cold start

The start injector time switch comes in several calibration values. These values determine the maximum temperature and maximum time that the switch will remain closed while the engine is being cranked. Specifications for switch calibration are stamped on the switch. Application information is available through parts and technical service bulletins.

injector for up to three seconds regardless of the status of the time switch. Maximum coolant temperature for ECU control is 113’F (45’C), above which the cold start injector will not operate from any source.



Alternative Method ofCold Cranking Enrichment Some engines have eliminated use of a cold start injector entirely. Starting with the '91 model year, cold start injectors have been eliminated on the 3E-E and 4A-FE engine. During cranking, the ECU looks at THW and lengthens injector pulse width sufficiently to start the engine.

Summary In this chapter you have learned that the fuel delivery system pumps fuel from the tank to the engine where it is delivered by an electronically controlled fuel injector.

The fuel pump delivers fuel with enough pressure and volume so the fuel pressure regulator can hold a constant pressure differential between intake manifold and fuel rail. Fuel which is delivered to the fuel rail but not injected into the cylinders is returned to the tank through a return pipe.

The fuel pump is energized by the circuit opening relay electrical circuit whenever the ignition switch is on and the engine is running or cranking. Depending on fuel demand, some pumps are operated at two speeds by routing current flow through or around a special current limiting resistor. The fuel pump electrical circuit has a diagnostic monitor built into the underhood check connector for diagnosis and testing.

Fuel injectors are electrically controlled by the ECU and are driven individually, in groups, or simultaneously, depending on engine application. Current flow through the injector coil is controlled by using a high resistance coil or a separate injector solenoid resistor.

To improve cold starting, some engines are equipped with a cold start injector system which is controlled by a start time switch and/or the ECU.




The EFI/TCCS Ignition System

Overview of Toyota EFI/TCCS Ignition ControlThe ignition systems used on today's EFI/TCCS equipped engines are not that much different from the ignition system used on the original 4M-E EFI engine. Primary circuit current flow is controlled by an igniter based on signals generated by a magnetic pickup (pickup coil) located in the distributor.

The ignition system has a dual purpose, to distribute a high voltage spark to the correct cylinder and to deliver it at the correct time. Ideal ignition timing will result in maximum combustion pressure at about 10' ATDC.

The most significant difference between TCCS and Conventional EFI ignition systems is the way spark advance angle is managed. The Conventional EFI system uses mechanical advance weights and vacuum diaphragms to accomplish this. Starting with the 5M-GE engine in 1983, the TCCS system controls ignition spark timing electronically and adds an ignition confirmation signal as a fail-safe measure.

There are two versions of electronic spark management used on TCCS equipped engines, the Electronic Spark Advance (ESA) and the Variable Advance Spark Timing (VAST) systems.

EFI #4 - TCCS IGNITION SYSTEM


Conventional EFI Ignition System

Spark Advance Angle Control In the Conventional EFI system, spark advance angle is determined by the position of the distributor (initial timing), position of the magnetic pickup reluctor teeth (centrifugal advance), and position of the breaker plate and pickup coil winding (vacuum advance). The spark advance curve is determined by the calibration of the centrifugal and vacuum advance springs.

Besides being subject to mechanical wear and mis-calibration, this type of spark advance calibration is very limited and inflexible when variations in coolant temperature and engine

detonation characteristics are considered. Mechanical control of a spark curve is, at best, a compromise. In some cases the timing is optimal; in most cases it is not.

Engine RPM Signal

To indicate engine rpm to the EFI computer, the Conventional EFI system uses the signal generated at the coil negative terminal (IG-). Because this system does not use ECU controlled timing, the rpm signal to the ECU has no impact on spark timing whatsoever. The IG signal is used as an input for fuel injection only.



Conventional EFI IgnitionSystem Operation When the engine is cranked, an alternating current signal is generated by the pickup coil. This signal is shaped in the igniter and then relayed through a control circuit to the base of the primary circuit power transistor.

When the voltage at the base of this transistor goes high, current begins to flow through the coil primary windings. When this signal goes low, coil primary current stops flowing, and a high voltage is induced into the secondary winding. At cranking speed, spark plugs fire at initial timing, a function of distributor position in the engine.

When the engine is running, spark timing is determined by the relative positions of the

pickup reluctor (signal rotor) and the pickup coil winding to each other. This relative position is controlled by the centrifugal advance weights and vacuum advance diaphragm positions.

As engine speed increases, the reluctor advances in the same direction as distributor shaft rotation. This is a result of the centrifugal advance operation.

As manifold vacuum applied to the vacuum controller is increased, the pickup coil winding is moved opposite to distributor shaft rotation.

Both of these conditions cause the signal from the pick-up coil to occur sooner, advancing timing.



TCCS Ignition SparkManagement, Electronic SparkAdvance (ESA), and VariableAdvance Spark Timing (VAST)

The advent of ECU spark management systems provides more precise control of ignition spark timing. The centrifugal and vacuum advances are eliminated; in their place are the engine sensors which monitor engine load (Vs or PIM) and speed (Ne). Additionally, coolant temperature, detonation, and throttle position are monitored to provide better spark accuracy as these conditions change.

To provide for optimum spark advance under a wide variety of engine operating conditions, a spark advance map is developed and stored in a look up table in the ECU. This map provides for accurate spark timing during any combination of engine speed, load, coolant temperature, and throttle position while using feedback from a knock sensor to adjust for variations in fuel octane.

TCCS engines use two versions of ECU controlled spark management, Electronic Spark Advance (ESA) and Variable Spark Timing (VAST).



To monitor engine rpm, the TCCS system uses the signal from a magnetic pickup called the Ne pickup. The Ne pickup is very similar to the magnetic pickup coil used with Conventional EFI. It has either four or 24 reluctor teeth, depending on engine application.

Engines equipped with the ESA system (and the 4A-GE engine with VAST) use a second pickup in the distributor called the G sensor. The G sensor supplies the ECU with crankshaft position information which is used as a reference for ignition and fuel injector timing. Some engines use two G sensors, identified as G1 and G2.

ESA Ignition System OperationIn the example above, when the engine is cranked, an alternating current signal is generated by a 24-tooth Ne pickup and a four-tooth G pickup. These signals are sent to the ECU where they are conditioned and relayed to the microprocessor.

The microprocessor drives a trigger circuit, referred to as IGt (TR1). The IGt signal is sent to the igniter to switch the primary circuit power transistor on and off.

While cranking, IGt fixes spark timing at a predetermined value. When the engine is running, timing is calculated based on signals from engine speed, load, temperature, throttle position, and detonation sensors.

The IGt signal is advanced or retarded depending on the final calculated timing. ESA calculated timing is considered the ideal ignition time for a given set of engine conditions.

If the ECU fails to see an Ne or G signal while it is cranking, it will not produce an IGt signal, thus preventing igniter operation.



VAST System OperationWhen the engine is cranked, an alternating current signal is generated by a four-tooth magnetic pickup in the distributor. This alternating current signal is sent directly to the igniter where it is conditioned into a square wave by a waveform shaping circuit.

While cranking, this square wave signal is sent to the ECU on the Ne wire and to the igniter power transistor. The ignition system delivers spark at initial timing under this condition.

When the engine starts and exceeds a predetermined rpm, the ECU begins sending the lGt signal to the igniter. The igniter switches to computed timing mode

and uses the IGt signal to operate the power transistor. Timing of IGt is based on information from various engine sensors.

Because the VAST system triggers the igniter directly from the magnetic pickup while cranking, the engine will start even if the IGt circuit to the igniter is open. If IGt signals are not received by the igniter once the engine has started, it will continue to run, defaulted at initial timing, using signals from the magnetic pickup.

The VAST system is only used on the 2S-E, 22R-E, 22R-TE, 4Y-E, and 4A-GE engines.



Igniter OperationWhen the IGt signal goes high, the primary circuit power transistor TR2 turns on, allowing cur-rent to flow in the coil primary winding. When the IGt signal goes low, the igniter interrupts primary circuit current flow, causing voltage induction into the coil secondary winding.

With the ESA system, the time at which the power transistor in the igniter turns on is further influenced by a dwell control circuit inside the igniter. As engine rpm increases, coil dwell time is increased by turning the transistor on sooner. Therefore, the time at which the transistor is turned on determines dwell while the time the transistor is turned off determines timing. Timing is controlled by the ECU; dwell is controlled by the igniter.

Controlling dwell within the igniter allows the same control over coil saturation time as the ballast resistance does with the Conventional EFI ignition system. It allows maximum coil saturation at high engine speeds while limiting coil and igniter current, reducing heat, at lower speeds.

Spark Confirmation IGf Once a spark event takes place, an ignition confirmation signal called IGf is generated by the igniter and sent to the ECU. The IGf signal tells the ECU that a spark event has actually occurred. In the event of an ignition fault, after approximately eight to eleven IGt signals are sent to the igniter without receiving an IGf confirmation, the ECU will enter a fail-safe mode, shutting down the injectors to prevent potential catalyst overheating.



ECU Detection Of Crankshaft Angle

ESA System In order to correctly time spark and injection events, the ECU monitors the relationship between the Ne and G signals. With most engines, the ECU determines the crankshaft

VAST System Because all engines which use this system have a simultaneous injection pattern (except the 4A-GE), a G signal is not necessary. The four-toothed pickup is designed to produce a pulse once every 180' of crankshaft rotation, signal timing determined by the position of the distributor in the engine. Distributor position determines Ne signal timing and, therefore, initial timing reference. The 4A-GE engine with VAST, because it uses grouped injection, utilizes a G sensor signal indicating camshaft position so the ECU can properly time each injector group.

has reached 10' BTDC of the compression stroke when it receives the first Ne signal following a G1 (or G2). Initial timing adjustment is critical as all ECU timing calculations assume this initial 10' BTDC as a reference point for the entire spark advance curve.

Ignition Timing Strategy The ECU determines ignition timing by comparing engine operating parameters with spark advance values stored in its memory. The general formula for ignition timing follows:

Initial timing + Basic advance angle + Corrective advance angle = Total spark advance.

Basic advance angle is computed using signals from crankshaft angle (G1), crankshaft speed (Ne), and engine load (Vs or PIM) sensors. Corrective timing factors include adjustments for coolant temperature (THW) and presence of detonation (KNK).



Distributor-Less Ignition System (DLI)

Used only on the 7M-GTE engine, DLI, as the name implies, is an electronic spark distribution system which supplies secondary current directly from the ignition coils to the spark plugs without the use of a conventional distributor. The DLI system contains the following major components:

1) Cam Position Sensor2) Igniter3) Ignition Coils (3)

Cam Position Sensor Very similar to the 7M-GE distributor without the secondary distribution system, the cam position sensor houses the Ne, G1, and G2 pickups. The Ne pickup reluctor has 24 teeth, its signal representing crankshaft speed. The G1 and G2 pickups produce signals near TDC compression stroke for cylinders #6 and #1, respectively. These signals represent standard crankshaft angle andcylinder identification.

Igniter The igniter is similar to those used on distributor type ignition systems but incorporates three separate primary circuits. The igniter determines timing of three primary circuits by the combination of IGdA and IGdB input signals from the ECU. The IGt signal is relayed by the igniter to the proper power transistor circuit to trigger the ignition event at the proper coil. The igniter also sends the standard IGf confirmation signal to the ECU for each ignition event which takes place.



Ignition Coils Each coil is connected in series between spark plugs of companion cylinders. For every engine cycle (720' of crankshaft rotation), ignition is carried out twice at each coil, both spark plugs firing simultaneously. One plug fires before TDC on the compression stroke while the companion fires at the same position before TDC on the exhaust stroke. This type of secondary distribution is referred to as waste spark.

The three ignition coils are mounted on the top of the engine to the upper section of the head cover. As you face the engine, the coil for the 1-6 cylinder pair is on your left. The coil in the center serves the 3-4 cylinder pair, and the coil to the right serves cylinder pair 2-5.



DLI System OperationWhen the engine is cranked, alternating current signals are generated by the 24-tooth Ne sensor and the two G sensors (G1 and G2). The G sensors are 360' out of phase.

The G sensors represent #1 and #6 pistons approaching TDC on the compression stroke. These signals are received by the ECU where they are conditioned and processed by the ESA microprocessor.

The ESA microprocessor serves two functions. It generates an IGt signal and generates cylinder identification signals, IGdA and IGdB, which allow the DLI igniter to trigger the correct coil while cranking the engine.

These signals are sent to the DLI igniter which electronically determines proper primary signal distribution based on the combination of IGdA and IGdB signals. The igniter distributes the IGt signal to the proper coil driver circuit and determines dwell period based on coil primary current flow. The ESA calculations for spark advance angle work the same as with distributor type ignition systems.

The table below shows how the igniter is able to calculate crankshaft position and properly distribute the IGt signal to the transistor driver circuit connected to the relevant ignition coil.



Ignition System Service Troubleshooting the Ignition System

No Spark Output The following procedures assume that a spark tester reveals no spark at two different cylinders while the engine is cranked. These procedures and specifications are general guidelines. Consult the appropriate repair manual for more specific information about the vehicle you are troubleshooting.

Preliminary checks

1) Ensure battery condition prior to ignition system analysis.

2) Check and confirm good connections at distributor, igniter, and coil.

3) Basic secondary leakage checks at coil and coil wire.

Primary circuit checks

1) Confirm power supply to igniter and coil positive (+) terminal. Confirm connections at coil positive and negative (-) terminals.

2) Using a test light or logic probe, check for primary switching at the coil (-) terminal while cranking engine. Blinking light confirms primary switching is taking place; check coil wire, coil secondary winding resistance, or secondary leakage in distributor cap.

3) The power transistor(s) in the igniter get their ground through the igniter case to the vehicle chassis; always confirm good ground continuity prior to trouble shooting.

4) Confirm coil primary and secondary windings resistance. Confirm primary windings are not grounded.

5) Confirm signal status from Ne and G pickups to ECU (ESA system) or to igniter (VAST system) using an oscilloscope or logic probe.

• If a fault is detected, check pickup(s) for proper resistance and shorts to ground. Check electrical connections.

• If signal amplitude is low, check signal generator gap(s).

6) Confirm signal status from ECU IGt circuit to igniter using an oscilloscope or logic probe.

7) On 7M-GTE, check power transistor in igniter. Bias transistor base using a remote 3 volt battery as power source. Use ohmmeter to check for continuity from primary circuit to ground (see procedure in repair manual for details).



8) Check pickup gaps and coil resistances against specifications. If gap and/or resistance is not within specification, replace faulty component.



Timing Will Not Advance Properly (VAST System) The following checks assume that the engine runs but timing will not advance.

The design of the VAST system will allow the ignition system to function at initial timing in the event that the IGt signal does not reach the igniter. If this condition occurs, the ignition system will be locked at initial timing regardless of engine speed or load. The ECU has no way to monitor for this fault, so there will be no indication of this condition other than a loss of engine performance.

To check for this condition:

1) Monitor the IGt wire at the igniter using an oscilloscope or logic probe.

2) If a good signal is being sent out on IGt, check the connection at the igniter.

3) Once connections are confirmed, the igniter is the last item left which can cause the problem.

Timing Seems Out of Range For Conditions (VAST or ESA) In some cases, driveability symptoms or a check of timing reveal advance which is out of range for input conditions. This situation could be caused by incorrect sensor information reaching the ECU.

An example of this type of problem can be illustrated by a manifold pressure sensor which is out of range low. Lower than normal voltage from the sensor would indicate a light load condition to the ECU. The ECU responds to light load operation by advancing the timing. If the vehicle is being operated under moderate to heavy load with too much spark advance, detonation will likely result.

When this type of condition is suspected, it is recommended to perform a standard voltage check of all major sensor inputs to the ECU. If any sensor is found out of normal range, it is a likely cause of the problem. The subject of sensor signal values is addressed in, "Electronic Engine Controls."



Adjustment Of Initial Ignition Timing All engines equipped with TCCS utilize a test terminal (T or TE1) somewhere under the hood. Early TCCS utilizes a two-terminal check connector in the wiring harness. This yellow body connector contains circuits T and E1, which when jumpered, default the TCCS system to initial timing. The location of this test terminal varies between applications. Refer to the appropriate repair manual for connector location.

A new design multipurpose check connector began phase-in starting with 1985 models. By 1986 model year, all vehicles are equipped with this new style connector. Connectors are typically located in the fender area on either side, or near the bulkhead, in plain view. With the advent of test terminals for the ECT, TEMS, SRS, and etc., the TCCS test terminal has been renamed TE1 to distinguish it from the others.

To check timing on any TCCS equipped engine:

1) Engine at normal operating temperature.

2) Jumper T (TE1) to El using SST 09843-18020 (or equivalent).

3) Wait for engine rpm to stabilize (speed may rise to I K to 1.3 K rpm for 5 seconds).

4) Use timing light to confirm initial timing as per repair manual procedure. • Make sure rpm is within specified range. • Adjust timing as necessary by rotating the distributor (cam position sensor on 7M-GTE).

5) Remove SST jumper.

6) Recheck timing; it should be advanced (at least 3' to 18') from initial with SST removed.



SummaryIn this chapter you have learned how the ECU electronically controls ignition timing, delivering spark at the optimum moment based on engine speed, load, temperature and quality of fuel. The spark advance curve is stored in a look up table in the ECU memory.

There are two types of ECU controlled spark advance systems used on Toyota TCCS equipped engines, the Variable Advance Spark Timing system (VAST) and the Electronic Spark Advance system (ESA). The main difference between these systems is the magnetic pickup in the distributor (Ne pickup) reports to the igniter on the VAST system and directly to the ECU on the ESA system.

An ignition confirmation signal is generated by the igniter which signals the ECU with each ignition event. The IGf signal is used to provide the ECU with a fail-safe fuel cutoff if ignition spark is lost.

The Distributorless Ignition system (DLI) provides secondary distribution by means of a three-coil waste spark system. Two companion spark plugs are connected to each end of the ignition coil secondary windings. These plugs fire simultaneously each time the cylinder pair approaches TDC, one spark igniting the mixture, the other wasted on the exhaust stroke.




Overview

The EFl/TCCS system is an electronic control system which provides Toyota engines with the means to properly meter the fuel and control spark advance angle. The system can be divided into three distinct elements with three operational phases.

The three system elements are:

• Input Sensors

• Electronic Control Unit (A Microcomputer)

• Output Actuators

ENGINE CONTROLS - INPUT SENSORS


The electronic control system is responsible for monitoring and managing engine functions which were previously performed by mechanical devices like carburetors, vacuum, and centrifugal advance units. In an electronic control system, these functions are managed in three phases.

• The input phase of electronic control allow the Electronic Control Unit (ECU) to monitor engine operating conditions, utilizing information from the input sensors.

• The process phase of electronic control requires the ECU to use this input information to make operating decisions about the fuel and spark advance systems.

• The output phase of electronic control requires the ECU to control the output actuators, the fuel injectors, and igniter to achieve the desired fuel metering and spark timing.

In this chapter, we will explore the details of the electronic control system hardware and software. The chapter starts with a thorough examination of the system's input sensor circuits and the ECU power distribution system. It concludes with a closer look at the ECU process functions and the control strategy use( for optimum fuel metering and spark advance angle control.

The Microcomputer The heart of the TCCS system is a microcomputer. A microcomputer is a device which receives information, processes it, and makes decisions based on a set of program instructions. The microcomputer exercises control over the output actuators to carry out these instructions.

The use of microcomputers has taken the science of engine management into the space age by increasing the speed with

which information can be processed and allowing the electronic control system to manage more engine functions. With the ability to process information so rapidly, the modern ECU is capable of carrying out its programmed instructions with extreme accuracy. Engine management can address virtually every condition the engine will encounter so that for any engine condition, the ECU will deliver optimum fuel and spark.

Evolution of Toyota's Electronic Fuel Injection Systems

Early Conventional EFI computers were first configured from analog circuits, and they controlled only fuel delivery and injection. The modem Electronic Control Units (ECU) utilize digital circuits and microprocessors which have served to improve EFI system capabilities.

Modern TCCS engine controls, introduced to the U.S.A. market in 1983, are capable of managing fuel delivery, idle speed control (ISC), electronic spark advance (ESA), and emissions systems with extraordinary speed and accuracy.

In the evolution of Toyota's fuel injection, three levels of electronic control refinements have taken place.

• Conventional EFI

• P7/EFI

• EFI/TCCS

The main difference between these systems is the capability of the ECU. These capabilities have grown from simple fuel control to the addition of self-diagnostics to the control of ignition spark advance and more. The following chart summarizes basic capabilities by system and can be used as a guide in identification and troubleshooting.



System identification is relatively simple.

• The Conventional EFI system has no check engine light.

• The P7/EFI system has a check engine light but has a mechanical advance distributor.

• The EFI/TCCS system has a check engine light and an electronic advance distributor.

The Input Sensors, Information Source for the ECU In an electronic control system, the ECU uses its sensors in much the same manner as we use our five senses. Our sense of touch tells us when things are hot or cold; our sense of hearing allows us to distinguish one sound from another; our sense of smell tells us when fresh coffee is brewing somewhere nearby. Sensors give the ECU similar abilities: the ability to feel the temperature of the engine coolant, to listen for the sound of detonation, and to smell the exhaust stream for the presence of sufficient oxygen.

This lesson on input sensors will address how each major ECU input sensor circuit works. Each sensor circuit will be broken down so you can see its individual components: the sensor, electrical wiring, and the ECU.



Overview

The EFl/TCCS system is an electronic control system which provides Toyota engines with the means to properly meter the fuel and control spark advance angle. The system can be divided into three distinct elements with three operational phases.

The three system elements are:

• Input Sensors

• Electronic Control Unit (A Microcomputer)

• Output Actuators



Input Sensors Used in Basic Injection and Spark Calculation

Engine Air Flow Sensing

Vane Type Air Flow Meters (Vs, General Information) The vane type air flow meter is located in the air induction system inlet pipe between the air cleaner and the throttle body. It is composed of the measuring plate, compensation plate, return spring, potentiometer, and by-pass passage. The sensor also incorporates the idle mixture adjusting screw (factory sealed), the fuel pump switch, and the intake air temperature sensor (which will be addressed later in this lesson). Because intake air volume is a direct measure of the load placed on an engine, the vane type air flow meter provides the most important input to the ECU for fuel and spark calculations.

When air passes through the air flow meter, it forces the measuring plate open to a point where it balances with the force of the return spring. The damping chamber and compensation plate prevent vibration of the measuring plate during periods of sudden intake air volume changes.

The potentiometer, which is connected to the measuring plate and rotates on the same axis, converts the mechanical movement of the measuring plate into a variable voltage signal. Movement of the measuring plate and the analog voltage signal produced by this sensor are proportional to the volume of air entering the intake manifold.

Vane Air How Meter Electrical Circuit The sensor movable contact is attached to the measuring plate and rides on a fixed resistor wired between the reference voltage input and the ground. As the volume of air entering the engine increases, the movable contact moves across the fixed resistor, causing a change in signal output voltage.

There are two designs of vane air flow meters used on Toyota L type EFI systems. The first design generates a signal which varies from low voltage at low air volumes to high voltage at high air volumes. The second design sensor has opposite signal characteristics. These sensors also operate on different reference voltages. Both sensor designs integrate an intake air temperature sensor into the air flow meter.



First Design Vane Air How Meter The first design air flow meter is found on all Conventional EFI engines and many later model TCCS equipped engines. This sensor has an electrical connector with seven terminals, four of which are used for air flow measurement.

Air Flow Sensor Terminal Identification(First Design Sensor)

The air flow meter and ECU are wired as shown in the diagram. Signal characteristics are depicted by the accompanying graph. The use of battery voltage, VB, as a sensor input necessitates the use of the Vc terminal as a constant reference signal for the ECU. This is because battery voltage may change with variances in electrical load and ambient temperatures. Without the use of a constant reference voltage, these changes would cause a change in the Vs signal value recognized by the ECU.



Second Design Air How Meter The second design air flow meter was introduced on the '85 5M-GE engine, and its use expanded with many late model TCCS equipped engines. This sensor has an electrical connector with seven terminals, three of which are used for air flow measurement.

Air Flow Sensor Terminal Identification(Second Design Sensor)

The air flow meter and ECU are wired as shown in the diagram; signal characteristics are depicted by the accompanying graph. The use of a regulated 5 volt reference eliminates the need for the VB terminal with this sensor circuit.

Resistors R1 and R2 provide self diagnostic capabilities and allow for a fail-safe voltage at the ECU in the event of an open circuit. These two resistors have a very high resistance value (relative to r1 and r2) and essentially have no electrical effect on the circuit under normal operating conditions. They will, however, affect the open circuit voltage measured on the Vs wire at the ECU.



Karman Vortex Air Flow Meter (Ks) The Karman vortex air flow meter is currently used on the 7M-GTE Toyota engine and the 2JZ-GE and 1UZ-FE Lexus engines. It is located in the air induction system inlet pipe between the air cleaner and the throttle body. The sensor is composed of a photocoupler and mirror, a vortex generator, and an integrated circuit (IC) which together, measure the frequency of the vortices generated by air entering the intake system.

When compared with the vane type air flow meter, the Karman vortex meter is smaller, lighter, and offers less restriction to incoming air. Similar to the vane type air meter, the

Karman vortex meter integrates the intake air temperature sensor into the meter assembly.

The sensor has an electrical connector with five terminals, three of which are used for air flow measurement.

Karman Vortex Air Flow MeterTerminal Identification



The Karman vortex air flow meter and ECU are wired as shown in the diagram. Signal characteristics are represented by the illustration of the variable frequency square wave. Because of the pull-up resistor wired between the Vcc and Ks circuit, the Ks signal will go to 5 volts if the circuit is opened.

When air passes through the air flow meter, the vortex generator creates a swirling of the air downstream. This swirling effect is referred to as a "Karman vortex." The frequency of this Karman vortex varies with the velocity of the air entering the air flow meter and other variables. The photocoupler and metal foil mirror are used to detect changes in these vortices.



The metal foil mirror is used to reflect light from the LED to the photo transistor. The foil is positioned directly above a pressure directing hole which causes it to oscillate with the changes in vortex frequency. As the mirror

oscillates, the 5 volt Vcc reference is switched to ground by a photo transistor within the sensor. The resulting digital signal is a 5 volt square wave which increases in frequency in proportion to increases in intake air flow.



Manifold Absolute Pressure Sensor The manifold absolute pressure sensor (sometimes referred to as vacuum sensor) is used on engines equipped with D type EFI. It is typically located somewhere on the bulkhead with a vacuum line leading directly to the intake manifold. It measures intake air volume by monitoring changes in manifold absolute pressure, a function of engine load.

The sensor consists of a piezoresistive silicon chip and an Integrated Circuit (IC). A perfect vacuum is applied to one side of the silicon chip and manifold pressure applied to the other side. When pressure in the intake manifold changes, the silicon chip flexes, causing a change in its resistance. The varying resistance of the sensor causes a change in signal voltage at the PIM (Pressure Intake Manifold) terminal.



The manifold absolute pressure sensor has an electrical connector with three terminals.

Manifold Absolute Pressure SensorTerminal Identification

The sensor and ECU are wired as shown in the diagram. As manifold pressure increases (approaches atmospheric pressure) there is a proportionate increase in PIM signal voltage. This analog signal characteristic is depicted in the accompanying graph.

TO check sensor calibration, signal voltage should be checked against the standards shown on the graph, and a voltage drop check should be performed over the entire operating range of the sensor.



Engine Speed and Crankshaft Angle Sensing On TCCS equipped engines, the Ne and G1 signals inform the ECU of engine rpm and crankshaft angle. This information, along with information from the air flow or manifold pressure sensor, allows the ECU to calculate the engine's basic operating load. Based on measured load, basic injection and spark advance angle can be accurately calculated.

Ne Signal (Number of Engine Revolutions) The Ne signal generator consists of a pickup coil and toothed timing rotor. The number of teeth on the signal timing rotor is determined by the system used. The Ne sensor produces an alternating current waveform

signal and is of critical importance to the ECU. If this signal fails to reach the ECU, the engine will not run.

G or G1 Signal (Group #1) The G signal generator is very similar to the Ne signal generator. The G1 signal represents the standard crankshaft angle and is used by the ECU to determine ignition and injection timing in relation to TDC.

Depending on engine, there are different variations of Ne and G1 signal generators. The following illustrations show the relationship between the Ne and G1 signals and the different variations of signal generators.



lGf Signal The IGf signal is generated by the igniter on EFI/TCCS systems. The ECU supplies a 5 volt reference through a pull-up resistor to the lGf signal generation circuit in the igniter. When a spark plug fires, the IGf signal generation circuit pulls the five volts to ground, causing a pulse to be sensed at the ECU. One pulse is generated by the igniter for each ignition event which is carried out.

IG Signal On Conventional EFI engines, the IG signal is used to inform the ECU of engine rpm. This signal is generated directly from the coil negative terminal or from an electrically equivalent point inside the igniter on the early

The IGf signal confirms that ignition has actually occurred. In the event of a failure to trigger an ignition event, the ECU will shut down injector pulses to protect the catalyst from flooding with raw fuel. Typically this fail-safe shutdown occurs within eight to eleven IGt signals after the IGf signal is lost. This condition can occur with any primary ignition system fault, an igniter failure, a problem with the IGf circuit wiring, or with a faulty ECU.

P-7 2S-E engine. Conventional EFI engines do not use an Ne or G sensor and do not use an IGf signal. The IG signal is also used by the ECU to trigger injection pulses; therefore, if this signal is lost, the engine will stall for lack of injection pulse.



Input Sensors Used For Injection and Spark Corrections

Water Temperature Sensor (THW) The water temperature sensor is typically located near the cylinder head water outlet. It monitors engine coolant temperature by means of an internally mounted thermistor. The thermistor has a negative temperature coefficient (NTC), so its resistance value decreases as coolant temperature rises. The accompanying resistance graph demonstrates this relationship.

The water temperature sensor is required because fuel vaporization is less efficient when the engine is cold. Internal engine friction is also higher during cold operation, increasing operating load. The THW signal is used by the ECU to determine how much fuel enrichment correction is necessary to provide good cold engine performance. In addition to fuel calculations, the THW signal plays a major role is almost every other function that the ECU serves.



The water temperature sensor has a two terminal electrical connector attached to either end of the thermistor element.

Water Temperature SensorTerminal Identification

The sensor and ECU are wired as shown in the diagram. Signal voltage characteristics are determined by the value of the pull-up resistor, located inside the ECU, either 2.7 KΩ or 5 M. The graphs accompanying the diagram give approximate voltage specifications. To determine which pull-up resistor a particular ECU uses, refer to the technical reference charts in Appendix B of this book.



Air Temperature Sensor (THA) The air temperature sensor monitors the temperature of air entering the intake manifold by means of a thermistor. This thermistor is integrated within the air flow meter on L type systems and located in the intake air hose just downstream of the air cleaner on D type systems. It has the same resistance characteristics as the water temperature sensor.



This sensor has a two-terminal electrical connector attached to either end of the thermistor element.

Air Temperature SensorTerminal Identification

The air temperature sensor and ECU are wired as shown in the diagram. Resistance and voltage signal characteristics are represented by the accompanying graphs.

An intake air temperature monitor is necessary in the EFI system because the pressure and density of air changes with temperature. Because air is more dense when cold, the ECU factors intake air temperature into the fuel correction program.



Throttle Angle and Closed Throttle Sensing

Throttle position sensors typically mount on the throttle body, directly to the end of the throttle shaft. Depending on engine and model year, Toyota EFI equipped engines use one of two different types of throttle position sensors. These sensors are categorized as on-off type and linear type. The linear type sensor is typically used on most late model Electronically Controlled Transmission (ECT) equipped vehicles.

The on-off type sensor circuits can be further broken down into first and second design. This sensor is typically used on manual or non-ECT transmission equipped applications.

All throttle sensors, regardless of design, supply the ECU with vital information about idle status and driver demand. This information is used by the ECU to make judgments about power enrichment, deceleration fuel cut-off, idle stability, and spark advance angle corrections.



On-Off Type Throttle PositionSensors (IDL & PSW)

The on-off type throttle position sensor is a simple switch device which, depending on application, either pulls a reference voltage to ground or sends a battery voltage signal to the ECU. The on-off throttle position sensors are electrically wired to the ECU as shown in the accompanying diagrams.

First Design On-Off Type SensorThe first design sensor is used on Conventional EFI engines. It utilizes a dual

position contact which switches a battery voltage signal to either the IDL or PSW inputs at the ECU. This switching action causes the voltage signal at the ECU to go high whenever the switch contacts are closed.

Referring to the voltage graph, IDL signal voltage is high when the throttle is closed and goes low when the throttle exceeds a 1.5' opening. PSW voltage is low until the throttle exceeds about a 70' opening; then it goes high.



Second Design On-Off Type SensorThe second design sensor, which is used on many late model TCCS equipped engines, utilizes a dual position contact to switch an ECU reference voltage to ground. This switching action causes the signal at the ECU to go low whenever the switch contacts are closed.

Referring to the voltage graph, IDL signal voltage is low when the throttle is closed and goes high when the throttle exceeds a 1.5' opening. PSW voltage is high until the throttle opens to about 70’; then it goes low.

The three wire electrical connector terminals are identified as follows.

1 st and 2nd Design On-Off ThrottlePosition Sensor Terminal Identification



On '83 and '84 Cressidas/Supras and '83 through '86 Camrys equipped with an Electronically Controlled Transmission (ECT), a modified sensor, which incorporates three additional signal wires designated L1, L2, and L3, is used. These signals represent throttle opening angles in between the 1.5' IDL and 70' PSW signals. The L1, L2, and L3 signals are used by the ECT system and are generated in a similar manner as the IDL and PSW signals on the 2nd design sensor. The TCCS ECU only uses the IDL and PSW signals from this sensor.

Linear Throttle Position Sensor (VTA) The linear throttle position sensor is mounted to the throttle body. It is composed of two movable contacts, a fixed resistor, and four electrical terminals. The two movable contacts move along the same axis as the throttle valve. One is used for the throttle opening angle signal (VTA) and the other for the closed throttle signal (IDL).



As the throttle opens, a potentiometer circuit converts the mechanical movement of the throttle valve into a variable voltage signal. The voltage produced by this sensor is proportional to the throttle valve opening angle.

The Linear Throttle Position Sensor has an electrical connector with four terminals.

Linear Throttle Position SensorTerminal Identification

The sensor and ECU are wired as shown in the diagram. As the throttle valve opens, the sensor VTA contact moves closer to the voltage source, causing a signal voltage increase.

At closed throttle, the IDL contact is held closed. This pulls the IDL signal circuit to ground. As the throttle opens, the IDL contact breaks, causing the digital IDL signal voltage to go from low to high. These signal characteristics are depicted in the accompanying graph.

Resistors R1 and R2 provide self diagnostic capabilities and allow for a fail-safe voltage at the ECU in the event of an open circuit. These two resistors have a very high resistance value and essentially have no electrical effect on the circuit under normal operating conditions. They will, however, affect the open circuit voltage measured on the VTA wire at the ECU.



Exhaust Oxygen Content Sensing (OX1) Exhaust oxygen sensors are used on Toyota EFI and EFI/TCCS equipped engines to provide air/fuel ratio feedback information to the ECU. This information is used to constantly adjust the air/fuel ratio to stoichiometry during warm idle and cruise operating conditions. The stoichiometric air/fuel ratio delivers one pound of fuel for each 14.7 pounds of air entering the intake manifold and results in the most efficient combustion and catalyst operation. When the electronic control system is using information from the oxygen sensor to adjust air/fuel ratio, the system is said to be operating in closed loop.

Exhaust oxygen sensor efficiency is dependent upon its operating temperature. The sensor will only generate an accurate signal when it has reached its minimum operating temperature of 750'F. Therefore, the oxygen sensor is typically located in the exhaust stream at the manifold collector. This location is close enough to the exhaust valves to maintain adequate operating temperature under most driving conditions and allows a representative exhaust sample from all cylinders.

Open and Closed Loop Operation In addition to promoting efficient combustion and catalyst operation, a stoichiometric air/fuel ratio also promotes excellent fuel economy. This relatively lean mixture is desirable during cruise and idle operation; however, other operating conditions often require a richer air/fuel ratio. When the electronic control system ignores signals from the oxygen sensor and does not correct the air/fuel ratio to 14.7:1, the system is said to be operating in open loop.

In order to prevent overheating of the catalyst and ensure good driveability, open loop operation is required under the following conditions:

• During engine starting

• During cold engine operation

• During moderate to heavy load operation

• During acceleration and deceleration

During open loop operation, the ECU ignores information from the exhaust oxygen sensor and bases fuel injection duration calculations exclusively on the other input sensors.



Exhaust Oxygen Sensors Toyota engines utilize two different types of oxygen sensors. The zirconium dioxide sensor is used on all engines except the '90 and later 4A-GE Federal and 3VZ-E California 2WD truck engines. These two engines use a titania oxide sensor.

To bring the system to closed loop operation more rapidly, many engines use a heated exhaust oxygen sensor. The heated sensor provides more accurate exhaust sampling during idle and low speed operation when exhaust temperatures are relatively low. Use of a heated sensor allows closed loop operation earlier during engine warm-up cycles and also allows more flexibility in oxygen sensor location. These factors help in meeting strict exhaust emissions control standards.

Engines produced for sale in California also incorporate a Sub-Oxygen Sensor which helps improve the efficiency of the catalyst system. This sensor is located after the catalyst and is used to fine tune the air/fuel ratio delivered by the injectors, helping to optimize catalyst efficiency.

Zirconium Dioxide Sensor The zirconium dioxide oxygen sensor is an electro-chemical device which compares the oxygen content of the exhaust stream with the oxygen in an ambient air sample. It consists of a zirconium dioxide (Zr02) element sandwiched between two platinum electrodes.

This sensor behaves very similar to a single cell battery. The electrodes act as the positive (+) and negative (-) plates, and the zirconium dioxide element acts as the electrolyte.

Rich air/fuel ratio: If the oxygen concentration on the inside plate differs greatly from that on the outside plate, as it would with a rich air/fuel ratio, electrons will flow through the Zr02 element to the plate exposed to the high oxygen concentration. During rich operating conditions, the inside, or positive plate, is exposed to a much higher concentration of oxygen than the outside, or negative plate. This creates a difference in electrical potential, or voltage, which is measured by a comparator circuit in the E CU.

Lean air/fuel ratio: When the air/fuel ratio becomes lean, the oxygen content of the exhaust gas increases significantly. Because both plates are now exposed to a relatively high concentration of oxygen, electrons balance equally between the two plates. This eliminates the electrical potential between the plates.

Zirconium Dioxide Oxygen SensorOperating Characteristics



Zr02 sensor voltage signal and ECU processing: The voltage signal produced by. the oxygen sensor is relatively small. During the richest operating conditions, this signal approaches 1000 millivolts (1 volt).

The Zr02 oxygen sensor is wired as shown in the diagram. Voltage characteristics are depicted in the accompanying graph.

As the voltage graph illustrates, the output of the Zr02 sensor acts almost like a switch. As the air/fuel ratio passes through the stoichiometric range, voltage rapidly switches from high to low.

The ECU comparator circuit is designed to monitor the voltage from the sensor and send a digital signal to the microprocessor. If sensor voltage is above the comparator switch point, z 1/2 volt, the comparator output will be high. If the sensor voltage is below the comparator switch point, the comparator output will be low. The microcomputer monitors the output of the comparator to determine how much oxygen remains in the exhaust stream after combustion occurs.



Titania Oxide Sensor This four-terminal device is a variable resistance sensor with heater. It is connected in series between the OX+ reference and a fixed resistance located inside the ECU. This circuit operates similarly to a thermistor circuit.

The properties of the thick film titania element are such that as oxygen concentration of the exhaust gas changes, the resistance of the sensor changes. As the sensor resistance changes, the signal voltage at the ECU also changes.

TITANIA OXIDE SENSORRESISTANCE CHARACTERISTICS

The titania sensor and ECU are wired as shown in the diagram. A one-volt potential is supplied at all times to the OX+ terminal of the sensor. The resistance value of the sensor changes abruptly as the stoichiometric boundary is crossed. The accompanying voltage and resistance graphs depict these characteristics and their influence on OX signal voltage.

The ECU comparator circuit is designed to monitor the voltage drop across R1. As the voltage drop across the sensor increases, the drop across R1 decreases and vice versa. This gives the OX signal voltage the same characteristic as the Zr02 sensor.

If sensor voltage drop is low, as it would be with a rich mixture, OX signal voltage will be above the comparator switch point, 450 millivolts, and the comparator output will be high. If the sensor voltage drop is high, OX signal voltage will be below the comparator switch point and the comparator output will be low.



Sub-Oxygen Sensor (OX2) The sub-oxygen sensor is used on California and some Federal engines. It is used to monitor the exhaust stream after the catalyst to determine if the air/fuel mixture is within the range for efficient converter operation.

The sub-oxygen sensor is identical to the Zr02 main oxygen sensor located ahead of the catalyst. Information from this sensor is used by the ECU to fine tune the air/fuel ratio and improve emissions.



Oxygen Sensor Heater Circuits (HT) Oxygen sensors work very efficiently when the sensing element temperature is above 750'F (400'C). At warm cruise, it is not difficult to maintain oxygen sensor temperatures at or above this point. However, when the engine is first started or when idling or when driving under very light load, the oxygen sensor can cool down, forcing the fuel system to return to open loop operation.

The oxygen sensor heater control system maintains sensor accuracy by turning on the heater element whenever intake air volume is low (exhaust temperatures are low under these conditions). By heating the sensor electrically, sensor detection performance is enhanced.

This allows feedback operation under conditions which might otherwise require open loop fuel control. The ECU monitors the following parameters and cycles the oxygen sensor heater on:

• When intake air flow is below a given point.

and

• coolant temperature is above approximately 32'F (O'C).

• specified time has elapsed after starting.

The oxygen sensor heater and ECU are wired as shown in the diagram. Whenever the above mentioned conditions are met, the ECU turns on the driver transistor to supply a ground path for heater current.



Other Inputs Affecting Injection and Spark Correction

Engine Cranking Signal (STA)STA is a digital signal which is used by the ECU to determine if the engine is being cranked. The signal is generated at the ST1 terminal of the ignition switch and is used by the ECU primarily to increase fuel injection volume during cranking.

The STA circuit is wired to the ECU as shown in the diagram. The ECU will sense cranking voltage at the STA terminal whenever the ignition is switched to the "start" position as long as the neutral or clutch switch is closed.



Engine Detonation (Knock) Signal (KNK)

Knock Sensor The knock sensor is a piezoelectric device mounted to the cylinder block which generates a voltage whenever it is exposed to vibration. When engine detonation occurs, vibration of the cylinder block causes the sensor to generate a voltage signal. The sensor signal varies in amplitude depending on the intensity of knock. Typically, detonation vibration occurs in the 7KHz range (7 thousand cycles per second). Knock sensor and ECU designs take advantage of this fact. There are two different types of knock sensors used on Toyota engines. The mass type sensor produces a voltage output over a wide input frequency range; however, its signal output is greatest at a vibration frequency of approximately 7KHz. With this type of sensor, the ECU uses a filter circuit to distinguish between background noise and actual engine knock. The resonance type sensor is tuned into a very narrow frequency band and only produces a significant signal voltage when exposed to vibrations in the 7KHz range. The ECU requires less complicated filter circuitry with this type of sensor.

ECU Detonation Control The ECU and knock sensor are wired as shown in the diagram. When engine detonation occurs, the ECU monitors knock sensor signal feedback to determine the degree of detonation taking place. This is accomplished by filtering out sensor signal voltage which does not go above preprogrammed amplitude parameters. Because other background noise and vibration cause some signal output from the knock sensor, the ECU is also programmed to filter out any signal which does not fall within certain frequency ranges.

When the ECU judges that detonation is taking place, it retards ignition timing until the knocking stops. Timing is then advanced back to calculated value or, if detonation again begins, retarded again until detonation is stopped. In this manner, the ignition system can be operated at maximum efficiency, on the borderline of detonation, while avoiding an audible "ping." In the event that the ECU continues to sense detonation, timing retard is limited based on a clamp value stored in memory. If the ECU determines that the knock retard is not functional, it will enter a fail-safe mode and fix the retard angle to prevent engine damage.



Altitude Sensing (HAC)

Some TCCS equipped engines like the 3F-E, 3VZ-E (Cab and Chassis), and the 7M-GTE incorporate an altitude sensor in the TCCS system to shorten injection duration when the vehicle is operated at higher altitudes.

Because the density of oxygen in the atmosphere is lower at high altitudes, the air volume measured by the air flow meter will not accurately represent actual oxygen entering the engine. This would result in a mixture which is excessively rich, causing emissions and driveability concerns.

The HAC sensor is integrated with the ECU on the 3-FE, 3VZ-E, and 1989 and later 7M-GTE engines. It is remotely mounted behind the glove box on the '87 and '88 7M-GTE Supra. The remotely mounted HAC sensor is wired to the ECU exactly the same as the manifold pressure sensor is wired on D type EFI. In fact, the HAC sensor circuit is electrically the same as a manifold pressure sensor circuit. The HAC sensor simply measures atmospheric pressure rather than intake manifold pressure.

The signal from the HAC circuit in the ECU is used to determine the fuel correction coefficient to be used after basic injection has been calculated. The accompanying graph represents how this correction factor affects final injection duration.



Stop Light Switch (STP) The stop light switch input to the ECU is used to modify the deceleration fuel cut program when the vehicle is braking. Whenever the STIR signal is high (brake pedal is depressed), fuel cutoff and resumption rpm is reduced to improve driveability characteristics of the vehicle.

In the event the STP signal is lost, fuel cut will take place at the standard deceleration speed, causing an objectionable feel when fuel is canceled.

The STP signal at the ECU will be low as long as the brake pedal is not applied. When the pedal is depressed, current flows through the normally open stop light switch to the stop lamps and the ECU, causing the STP voltage to go high.



The ECU, Process Center of theElectronic Control System

The ECU is an extremely reliable piece of hardware which has the capability to receive and process information hundreds of times per second. At the heart of the ECU is the microprocessor. It is the processing center of the ECU where input information is interpreted and output commands are issued. The process and output functions of the ECU can be divided into the following six areas:

• Fuel Injection Control

• ESA / VAST Spark Advance Control

• Idle Speed Control

• Self Diagnosis

• Related Engine and Emissions Control

• Failure Management (fail-safe and back-up)

Fuel, spark, and failure management functions will be covered individually in this chapter. Idle Speed Control, related engine systems, emissions control systems, and the self diagnosis system will be the subject of chapters 6, 7, 8, and 9, respectively.

ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONS


ECU Power Distributionand EFI Main Relay Circuits

The ECU cannot properly function without dependable power feeds and ground circuits. The power distribution system involves several electrical circuits, protection devices, relays, and grounds.

ECU Power Feeds

The ECU receives its ignition-switched power from the EFI main relay on all of Toyota's EFI systems. In addition to the ignition +B power feed, all P7 and TCCS ECUs have a direct battery feed, identified as BATT, supplied from either the EFI, STOP, or ECU +B fuse. The EFI main relay +B output is the power source which feeds the ECU and related engine control circuits. The direct battery feed (terminal BATT) serves to maintain voltage to the ECU keep alive memory when the ignition switch is off. Conventional EFI has no keep alive memory capabilities and, therefore, uses only an ignition switched power feed from the EFI main relay.

Main Relay CircuitsToyota utilizes several different EFI Main Relaycircuits depending on application. These circuitscan be categorized into four distinct types.1) Dual contact EFI Main Relay, ignition switch controlled2) Single contact EFI Main Relay, ignition switch controlled3) Dual EFI Main Relays, ignition switch or ECU controlled4) Single contact EFI Main Relay, ECU controlled

Generally speaking, the EFI Main Relay supplies current to the following major circuits:

• ECU +B and +B1

• Injectors (dual relay or dual contact relay only)

• Circuit opening relay (power contact and pull-in windings)

• Air flow meter VB circuit (when so equipped)

• Output Actuator Vacuum Switching Valves (VSV)

- Fuel Pressure Up (FPU)

- Exhaust Gas Recirculation (EGR)

- Throttle Opener

• ISC motor/solenoid windings

• Check connector +B terminal



Because the EFI Main Relay supplies battery voltage to the +B terminal of the check connector when the ignition switch is in the run position, this is an excellent place to perform a quick check of the relay function.

Dual Contact (Single Relay), Ignition Switch ControlledThis EFI Main Relay configuration is used on the Conventional EFI system. It uses separate power contacts to supply current to the fuel injector/ignition circuits and the ECU/circuit opening relay circuit. This limits current flow that the ECU power contact must handle.

This configuration improves the reliability of the relay, reduces possible voltage drop, and also isolates any inductive noise from the injectors to the EFI Computer by utilizing the battery as a large capacitor.

When the ignition switch is turned to the "run" or "start" position, current is supplied to the pull-in winding of the relay. Pull-in ground is wired directly to the vehicle chassis. The only power feed to the ECU on this system is the +B circuit.

Single Contact, Ignition Switch Controlled This EFI Main Relay circuit is one of the most popular power distribution schemes used on late model TCCS equipped engines. It is used on most applications without a stepper type Idle Speed Control Valve (ISCV).

When the ignition switch is turned to the "run" or "start" position, current is supplied to the pull-in winding of the relay. Pull-in ground is wired directly to the vehicle chassis. ECU BATT voltage is supplied from the STOP fuse on these applications.



Single Contact, ECU Controlled This EFI Main Relay circuit is used exclusively on applications equipped with the stepper type Idle Speed Control Valve. This relay is powered by the ECU rather than the ignition switch to allow control of the relay for approximately two seconds after the ignition is switched off. This allows the ECU to step the ISCV back to engine restart position after ignition power down.

When the ignition switch is turned on or engine cranked, the ECU receives a voltage signal at the IG SW terminal. This causes the ECU to supply current from the MREL terminal to the EFI Main Relay pull-in winding. The pull-in winding is grounded directly to the vehicle chassis. ECU BATT voltage is supplied from the EFI fuse on these applications.

When the ignition switch is turned off, the ECU will maintain current flow through the EFI Main Relay pull-in winding for a few seconds after power down to allow time to reset the stepper ISCV.

Dual Relays, Ignition Switchor ECU Controlled This configuration utilizes two separate relays identified as EFI Main Relay #1 and EFI Main Relay #2. Relay #2 supplies current to the fuel injector circuit. Relay #1 supplies current to the ECU, Circuit Opening Relay, and other circuits depending on application. If a stepper ISCV is used ('85 and '86 5M-GE), the ECU will drive relay #1 so the ISCV can be operated after the ignition is switched off.



ECU Grounds and Quick Checks No electrical circuit will function normally without a dependable ground. Toyota EFI systems use a redundant ground system which significantly reduces the chance of ground problems; however, this circuit should never be overlooked when troubleshooting ECU related systems.

The E2 circuit serves as a signal return or sensor ground. Referring to an EWD, you will notice that the throttle position sensor, water and air temperature sensors, and air flow meter all flow current to ground through circuit E2. The ECU supplies a chassis ground through the E1 circuit which typically terminates somewhere on the engine.

Circuits E01 and E02 serve as grounds for the fuel injector driver circuits. To provide a redundant ground for the ECU, these two grounds are tied to the E1 circuit through a diode. In the event that the E1 wiring to chassis is open circuit, E1 circuit current could flow through the diode to ground. The diode serves to prevent voltage spikes from the injectors from interfering with other ECU circuits.

It is not uncommon for many or even all ECU grounds to terminate at the same point and fasten to the engine with the same fastener. Sometimes a ground fault is due to one fastener being left loose after a service procedure has been performed.

It is a fairly simple task to confirm the integrity of all ECU ground circuits in fairly short order. Two methods can be used to identify and isolate a ground fault; these are the circuit continuity check and the voltage drop check. These procedures along with checks of the power distribution circuits are addressed in exercises 5-1 and 5-2.



Fuel Injection Control



Injector Timing

Injection Timing Control Injection timing control determines when each injector will deliver fuel to its corresponding intake port. There are three different methods of injector timing used on Toyota engines, depending on application. These methods are Simultaneous, Grouped, and Independent injection.

Simultaneous Injection All injectors are pulsed simultaneously by a common driver circuit. Injection occurs once per crankshaft revolution just prior to the crankshaft reaching TDC cylinder *1. This means that twice per engine cycle one half of the calculated fuel is delivered by the injectors. This is the simplest and most common injection timing method in use.

Grouped Injection Injectors are grouped into pairs. The pairs consist of two consecutive cylinders in the firing order; each pair is driven by a separate driver circuit. Four cylinder engines use two groups, six cylinder engines three groups, and the 1UZ-FE V8 engine uses four groups of injectors.

Injection is timed to deliver fuel immediately preceding the intake stroke for the leading cylinder in the pair. The entire group is pulsed once per engine cycle, delivering the entire calculated charge of fuel. This timing method ensures that fuel does not linger behind the intake valve, thereby, reducing emissions, improving fuel economy and throttle response.

Independent Injection Injectors are driven independently and sequentially by separate driver circuits. Injection is timed to deliver the entire fuel charge just prior to each intake valve opening. This timing method provides optimum engine performance, emissions, and fuel economy.



Input Signals Required to Pulse Injectors There are three signals which are necessary to operate the fuel injectors. These are the Ne, G, and IGf signals. Inside the ECU, the Ne Signal is used to produce an injection chive signal. The G signal is used to determine the timing of the injection signals. The IGf signal is monitored for fuel delivery fail-safe. (With Conventional EFI, the IG signal is used to produce the injection drive signal.)

The ECU cannot pulse the injector without an Ne signal and will not start or run if this signal is not present. If the G signal is not present while cranking the engine, the ECU will not be able to identify when to produce the injection signal. The result will be the same, no injection pulse. If the IGf signal is not present, the ECU will go into fuel fail-safe by stopping injection pulses.

If, however, the ECU loses the G signal with the engine running, the engine will continue to run because the timing of injection signals is locked in once the engine starts.



Injector Operating Modes There are two injection operating modes used by the ECU, depending on engine operating conditions. These modes are called synchronous and asynchronous.

Synchronous Injection Synchronous injection simply means that injection events are synchronized with ignition events at specific crankshaft angles. Synchronous injection is used a great majority of the time.

Asynchronous Injection Asynchronous injection is only used during acceleration, deceleration, and starting. It occurs independently of ignition events based on change in idle contact (IDL) or start switch (STA) status without regard to crankshaft angle.



ECU Control of Injector Duration

An Overview of Injection Duration Calculations Determination of final injection pulse width is the function of a three-step process.

Step 1, Basic Injection Duration The first step involves calculation of basic injection duration. Input sensors used in basic duration calculation are:

• Air Flow Meter (Vs or Ks) • Manifold Pressure Sensor (PIM) • Engine rpm (Ne)

The ECU calculates basic injection duration based upon engine speed and air flow volume. These two inputs considered together establish an engine load factor. The ECU monitors the Air Flow Meter signal or Manifold Pressure Sensor for intake air volume information and the Ne signal for engine speed information.

• As either of these parameters increase, injection duration is increased.

Step 2, Injection Duration Correction Factors The second step involves duration corrections. Input sensors used for injection duration corrections are:

• Engine Water Temperature (THW)• Intake Air Temperature (THA)• Throttle Angle (VTA or IDL & PSW)• Exhaust Oxygen Content (OX)

Once basic injection duration is calculated, the ECU must modify the injection duration based on other changing variables. Variables considered in the correction calculation are coolant and intake air temperature, throttle position and exhaust oxygen sensor feedback (when operating in closed loop).

• As engine and intake air temperatures move from cold to warm, injection duration is reduced.

• As the throttle opens (IDL contact break), injection frequency is momentarily increased.

• Fuel injection duration swings back and forth between longer to shorter durations to correct conditions detected by the exhaust oxygen sensor.

Step 3, Battery Voltage Correction The final step is a battery voltage correction. The input signal used in battery voltage corrections is: 0 Battery Voltage (+B)

There is an operational delay between the time the ECU sends the injection signal to the driver circuit and the actual opening of the injector. This delay changes with the strength of the magnetic field around the injector coil. The delay increases as battery voltage falls.

To determine final injection duration, the ECU corrects for injector opening delay by using a battery voltage correction coefficient.

• The battery voltage correction coefficient increases injection duration as sensed battery voltage falls.



ECU Injection StrategyWhile StartingPrime Pulse Because the rpm and intake air volume signals are erratic at cranking speed, injection duration calculation is done differently while the engine is cranking, compared to all other operating conditions.

Starting Injection Control To provide accurate fuel injection duration during cranking periods, the ECU uses a program which determines a basic injection volume based on engine coolant temperature. Once a basic injection duration is calculated, corrections are made for intake air temperature and battery voltage (which is typically low under cranking load).

• Basic injection duration while cranking is increased at low coolant temperatures.

• Injection duration while crankingis corrected for intake air temperatureby increasing duration at low intake airtemperatures.

• To prime the engine upon initial cranking, all injectors are pulsed in an asynchronous mode one time immediately after a G and Ne signal are received.

• Injection duration while cranking is

corrected for battery voltage by increasing injection duration at lower voltage.

The graph represents the basic cranking enrichment strategy used by the ECU. Note that at temperatures below freezing, basic injection duration increases drastically to overcome the poor vaporization characteristics of fuel at these temperatures.



Engine Running InjectionDuration Calculation

After Start-up Enrichment To stabilize the engine immediately after starting, for a short period of time after starting, the ECU supplies extra fuel to the engine to ensure a smooth transition from cranking to running. The maximum enrichment value is determined by the coolant temperature signal, THW.

Basic Injection CalculationOnce the engine has stabilized, engine rpm information and intake air volume measurements are used to determine basic injection duration.

• As intake air volume increases, injector duration increases.

• As engine rpm increases, injector frequency increases.

Injection Corrections A correction coefficient is calculated by determining the values of the various input sensors. This correction coefficient is used to modify the basic injection duration value to achieve a corrected injection duration value.

Correction For Intake Air Temperature The density of intake air varies with temperature. The colder the air, the denser it becomes. For this reason, a correction coefficient is used for changes in air temperature.

Referring to the coefficient graph, note that a standard air temperature of 68'F (20'C is used. At this temperature, the correction factor is 1.0.

For example, a correction factor of 1.0 means that no correction is made from the basic calculation. A coefficient of 1.1 means that injection duration is being increased by a factor of 10% while a coefficient of 0.9 means that injection duration is being decreased by a factor of 10%.

• As intake air temperature falls below the standard temperature, the correction coefficient increases and injection duration is increased (and vice versa).



Correction For Coolant Temperature(Warm-up Enrichment) When the engine is cold, fuel vaporization is relatively poor until the intake manifold warms up. To prevent lean driveability problems associated with this condition, the ECU enriches the air/fuel ratio accordingly based on engine coolant temperature.

The correction coefficient graph above shows a standard value of 158'F (70'C).

• At temperatures below 158'F, basic injection calculations are increased.

• At extremely cold temperatures, injection duration can be increased to almost double normal warm engine values.

Power Enrichment CorrectionWhen the ECU determines that the engine is being operated under moderate to heavy load, it increases injection duration values by up to 20% to 30%. This power enrichment program is based on information received from the air flow meter or manifold pressure sensor, the throttle position sensor and engine rpm.

• As engine load increases, injection duration is increased.

• As engine rpm increases, injection frequency increases at the same rate.

Battery Voltage Correction Because of the injector opening delay which varies with charging system voltage, the ECU must modify the corrected injection duration by a battery voltage correction coefficient to achieve a final injection duration value.

The final injection duration determines the quantity of fuel which is delivered to the engine.



Closed Loop Air/Fuel Ratio CorrectionUnder certain operating conditions, primarily cruise and idle, the ECU corrects the injection duration value based on signals from the exhaust oxygen sensor. This feedback correction is necessary to promote better vehicle emissions control.

By achieving more accurate fuel metering, the oxygen content of the exhaust stream is held within a very narrow range which supports the most efficient operation of the three-way catalyst (TWC).

Stoichiometry and Catalyst Efficiency The accompanying graph represents the efficiency of a three-way catalyst system at varying air/fuel ratios. As the graph clearly shows, the catalyst is most efficient in a narrow air/fuel ratio range.

The theoretical or ideal air/fuel ratio at which all tail pipe emissions are best converted is referred to as stoichiometry. The stoichiometric air/fuel ratio occurs around 14.7 to 1 (14.7 pounds of air for each pound of fuel).

It is important to note that the primary reason for using a closed loop fuel control system is to satisfy the requirements of the three-way catalyst system.



Closed Loop OperationClosed loop operation simply means that the ECU is making air/fuel ratio corrections based on oxygen sensor information. Although the ECU can calculate injection duration very accurately without using information from the oxygen sensor, closed loop control brings the air/fuel ratio within the extremely narrow operating parameters of the three-way catalyst (TWC).

The oxygen sensor monitors the oxygen concentrations in the exhaust stream and outputs a voltage signal to the ECU. This signal allows the ECU to determine whether the air/fuel ratio is leaner or richer than the theoretical value necessary for the best catalyst conversion efficiency.

• Exhaust oxygen sensor voltage signal above 1/2 volt indicates an air/fuel ratio richer than stoichiometry. 'Me ECU will reduce fuel injection duration to correct this condition.

• Exhaust oxygen sensor voltage signal below 1/2 volt indicates an air/fuel ratio leaner than stoichiometry. The ECU will increase fuel injection duration to correct this condition.

• During normal closed loop operation, the oxygen sensor signal rapidly switches between these two conditions (at a rate of more than eight times in ten seconds at 2500 rpm). Small injection duration corrections take place each time the signal voltage switches from high to low and back again.

The closed loop correction coefficient ranges from 0.8 to 1.2 (that is, +20% from the basic fuel calculation). If the air/fuel ratio goes out of the ECU's range of correction, the ECU will typically set a diagnostic code and return to open loop operation.

In a closed loop control system, the command corrects the condition.

• Oxygen sensor monitors exhaust condition

• ECU commands injectors to correct condition

• Oxygen sensor indicates correction accuracy

• ECU again commands injectors to correct condition



Open Loop OperationOpen loop operation means that the ECU is not correcting the air/fuel ratio based on oxygen sensor information. The ECU ignores exhaust oxygen sensor information even if the sensor is detecting an excessively rich or lean mixture. There are certain operating conditions where it is not desirable to operate the system in closed loop due to risk of catalyst overheating and driveability concerns. These conditions are:

• Engine starting• Cold engine operation• Moderate to heavy load operation

In open loop operation, a correction coefficient of 1.0 is used.

Acceleration and Deceleration Corrections When the engine operating conditions are in transition, either accelerating or decelerating, the injection volume must be increased or decreased slightly to improve engine performance and fuel economy. The input sensor signals used and the enrichment or enleanment strategies used vary with engine application.

Acceleration EnrichmentAs the engine is accelerated, a momentary lean condition exists as the throttle begins to open (this is due to the fact that fuel is more dense than air and cannot move into the cylinder as quickly). To prevent a stumble or hesitation, the ECU uses an acceleration enrichment fuel strategy. When the IDL signal goes from on to off, the ECU delivers an acceleration enrichment fuel pulse.

• As the IDL contact opens, the ECU commands all injectors to simultaneously deliver an extra asynchronous injection pulse.

On Conventional EFI engines, this pulse is delivered at the moment the IDL contact breaks. On EFI/TCCS engines, this pulse is delivered synchronous with the Ne signal which follows the IDL contact break.

Deceleration Fuel CutDuring closed throttle deceleration periods from higher engine speeds, fuel delivery is not necessary. In fact, deceleration emissions and fuel economy are adversely affected if fuel is delivered during deceleration.

To prevent excessive decel emissions and improve fuel economy, the ECU stops injection pulses completely during certain deceleration conditions.

• When the IDL contacts close with engine rpm above a given speed, the ECU cuts injection operation completely.

• When the engine falls below the threshold rpm, or when the throttle is opened, fuel injection is resumed.

Referring to the graph, fuel cutoff and resumption speeds are variable, depending on coolant temperature, A/C clutch status, and SIT signal.

• With A/C clutch on, fuel cutoff and resumption speeds will be increased.

• With the stop light switch on, fuel cutoff and resumption speeds will be decreased (some applications only).



Engine Over-rev Fuel CutoffTo prevent potential engine damage, a revlimiter is programmed into the ECU. Any time engine rpm exceeds the pre-programmed threshold, the ECU cuts fuel delivery. Once rpm falls below the threshold, fuel delivery is resumed.

Over-rev rpm threshold varies depending on engine design and application but typically runs in the 6500 to 7500 rpm range, usually cutting fuel slightly above the engine's red line rpm.

Vehicle Over-speed Fuel CutoffOn some vehicles, fuel injection is halted if the vehicle speed exceeds a predetermined threshold programmed into the ECU. Fuel injection resumes after the speed drops below this threshold.



Spark Advance Control

Electronic Spark Advance (ESA)Variable Advance Spark Timing (VAST)

Introduction To ECUSpark Advance Controls

The Advantage of ECUControlled Spark TimingTo maximize engine output efficiency, the ignition spark must be delivered at the precise moment which will result in maximum combustion chamber pressure occurring at about 100 ATDC. The amount of ignition spark advance, or lead time required to achieve this, will vary depending on many factors.

For example, because fuel bum time remains relatively constant, spark lead time must be increased as engine rpm increases. Because fuel has a tendency to detonate under heavy load conditions, spark lead time must be decreased as manifold pressure and intake air flow increase.

Engines equipped with Conventional and P7/EFI systems use a mechanical advance distributor to accomplish changes in spark lead time. The centrifugal (governor) advance increases spark lead time as engine rpm increases, and the vacuum advance decreases lead time as manifold pressure increases.

When all of the variables which affect optimum timing are considered, there are many more factors which influence required spark lead time. The coolant temperature, quality of fuel, and many other engine operating conditions can significantly impact ideal ignition time.

To provide for optimum spark advance under a wide variety of engine operating conditions, a spark advance map is developed and stored in a look up table in the ECU. This map provides for accurate spark timing during any combination of engine speed, load, coolant temperature, and throttle position while using feedback from a knock sensor to adjust for variations in fuel octane.

Prior to strict emissions and fuel economy standards, mechanical control of spark advance was adequate to accomplish reasonable engine performance and emissions control. However, in the automotive environment of the '90s, adequate is not good enough.



Two ECU Spark Advance ControlSystems Used By Toyota There are two distinctly different ECU controlled ignition systems in use on TCCS equipped engines. These systems are known as Electronic Spark Advance (ESA) and Variable Advance Spark Timing (VAST). Both systems accomplish the same goal; they provide ideal ignition timing under a wide variety of engine operating conditions.

You also learned the mechanics of how the ESA and VAST systems signal the igniter and fire the ignition coil. You have learned the system hardware. The objective of this lesson is to identify the process the ECU uses to calculate optimum spark advance angle under a wide variety of operating conditions. The ECU program which accomplishes this is the system software.

ECU Control Of Spark Advance Angle

Overview Of Advance Angle Calculation Determination of optimum spark advance angle is the function of a three-step process.

Step 1, Initial Timing AdjustmentThe first step involves correct adjustment of initial timing. The input sensor used by the ECU to determine initial timing is: 0 Standard Crankshaft Angle (G1, G2, and Ne)

The initial timing adjustment is critical to proper operation of the ECU controlled spark advance system. Initial timing is a function of the physical position of the distributor in the engine and becomes the base upon which all advance functions are added. Once the initial timing is adjusted properly, it will not change.

• If distributor position in the engine is changed, the relationship between Ne and G signals to TDC changes.

• Any deviation from specified initial timing will cause an equal amount of error in the final spark advance angle.



Step 2, Basic Advance AngleThe second step involves calculation of the basic advance angle. Input sensors used in basic advance angle calculation are:

• Intake Air Volume (Vs or Ks)

• Intake Manifold Pressure (PIM)

• Engine rpm (Ne)

The basic advance angle is primarily a function of inputs from the engine rpm and intake air volume sensors. This calculation is equivalent to the combined centrifugal and vacuum advance on a mechanical distributor.

• As engine rpm increases, spark angle is advanced.

• As intake air volume (engine load factor) increases, spark angle is retarded.

Step 3, Corrective Advance AngleThe final step in determining optimum or final spark advance angle is calculation of corrective advance angle. Input sensors used in corrective advance angle calculations are:

• Starting Signal (STA)

• Engine Water Temperature (THW)

• Throttle Angle (VTA or IDL & PSW)

• Knock Detection (KNK)

• Altitude (HAC)

• Electronically Controlled Transmission (ECT)

The biggest advantage of ECU controlled spark advance is the system's ability to adjust timing for all possible variables in the ideal advance angle equation. The corrective advance angle calculation accomplishes this by fine tuning the advance angle for changes in coolant temperature, engine detonation, transmission shift status, altitude, accessory status, and other variables.

• ECU advances spark angle for cold engine operation and retards for over-temperature conditions.

• ECU retards spark angle when detonation is detected.

• ECU advances spark angle for high altitude operation (models equipped with HAC sensor).



ECU Spark AdvanceStrategy While Starting

ESA SystemEngine starting: During starting, when engine speed is below approximately 500 rpm (or when STA signal is high), spark advance angle (IGt signal) is fixed at initial timing. A Backup IC located in the ECU generates a reference timing signal which is output to the microprocessor and the IGt line to the igniter. The reference signal represents base timing and is calculated based on inputs from the G1 and Ne sensors.

VAST SystemEngine starting: During starting, when below a predetermined rpm, no IGt signal is sent from the ECU to the igniter. The ignition coil is driven by the back-up circuit in the igniter at initial timing.

Engine running: Once the engine starts, timing of the IGt signal is controlled by the microprocessor in the ECU. Based on inputs from various sensors, a basic and corrective advance angle are calculated. The final spark advance angle consists of the sum of the initial, basic, and corrective spark advance angles.

Engine running: Once the engine starts, the ECU sends an IGt signal back to the igniter; the ignition coil is driven by this signal at computed timing.



ECU Spark Advance StrategyWhile Running

Basic Ignition Advance AngleThe ECU calculates the basic advance angle by evaluating engine rpm and intake air volume signals. These sensors' signals have the most significant effect on basic timing calculation.

There are other sensor inputs which also affect the basic spark advance angle. The A/C compressor clutch signal advances basic spark angle when the IDL contacts are on (on some engines), and on the 3S-GTE engine, basic advance angle is retarded if the ECU judges that regular fuel is being used, based on signals from the engine knock (KNK) sensor.

Corrective Ignition Advance Angle

Engine Temperature CorrectionsTo improve cold driveability, the ECU advances spark angle. The ECU considers intake air volume and the status of the IDL contact to determine how much cold advance to add to the basic spark calculation.

As the engine temperature approaches overtemp, the ECU will advance spark when the IDL contact is on, to prevent overheating. When the IDL contact is off, the ECU will retard spark to prevent detonation. Advance and retard shown on the graph are corrections to the basic advance angle.



Fuel Feedback IdleStabilization CorrectionTo prevent surging due to closed loop air/fuel ratio swings, when the IDL contacts are on, the ECU advances timing as lean commands are sent to the injectors (fuel injection volume decreased). This very small amount of advance added to the basic advance angle serves to stabilize engine idle quality.

Engine Load Idle Stabilization Correction When engine rpm changes at idle due to increased load, the ECU adjusts timing to stabilize idle speed. The ECU constantly monitors and calculates average engine speed. If the average speed is determined to go below a pre-programmed target rpm, the ECU will add advance to the basic spark angle to help re-establish the target idle speed.

Detonation CorrectionThe ECU constantly monitors the signal from the knock sensor to determine when detonation occurs. When detonation is sensed, basic advance angle is retarded in varying degrees, depending on the strength of the knock sensor signal. Once detonation stops, the ECU gradually cancels the retard, allowing timing to return to the basic advance angle.

The detonation correction strategy allows the engine to operate at optimum timing regardless of fuel octane, maximizing engine performance when high octane fuel is used. On some engines, this system only operates in a closed loop mode under load (vacuum below approximately 8 inches of mercury). Other engines operate in ignition closed loop under all engine load ranges.



ECT (Transmission) Shift CorrectionOn some applications with integrated ECT controls, the Engine and Transmission ECU retards the basic advance angle temporarily during gear shifting. This strategy helps reduce shift shock by reducing engine torque momentarily, just as the transmission shifts. The amount of retard varies depending on the status of engine and ECT sensor inputs.

High Altitude CorrectionThis strategy, which is used only on applications with High Altitude Compensation (HAC) capabilities, improves engine performance and idle quality during high altitude operation by advancing timing over the basic calculated spark angle.

EGR Flow CorrectionThis strategy advances timing from the basic calculation when the IDL contact is off and the ECU is commanding EGR flow. This correction allows the engine to operate more efficiently because it resists detonation when EGR is introduced into the cylinders.

SummaryIt is possible that minor calibration faults in key system inputs can have a significant effect on calculated spark advance, resulting in degraded driveability. When performance problems arise which appear to be the result of inaccurate timing advance calculation, do not overlook calibration of all relevant input sensors which influence timing during the affected driving mode. The best way to confirm sensor calibration is by becoming familiar with, and performing, the ECU Standard Voltage Check procedures.



Purpose of ECU ControlledIdle Speed Control Systems

The Idle Speed Control (ISC) system regulates engine idle speed by adjusting the volume of air that is allowed to by-pass the closed throttle valve. The ECU controls the Idle Speed Control Valve (ISCV) based on input signals received from various sensors. The system is necessary to provide stabilization of curb idle when loads are applied to the engine and to provide cold fast idle on some applications. The Idle Speed Control system regulates idle speed under at least one or more of the following conditions, depending on application:

• Fast Idle• Warm Curb Idle• Air Conditioner Load• Electrical Load• Automatic Transmission Load

Difference BetweenMechanical Air Valvesand ECU Controlled ISCV The ECU controlled ISC systems addressed in this chapter should not be confused with the mechanical air valves which were addressed in Chapter 2, "Air Induction System." The ISC valve is totally controlled by the ECU based on inputs received from the various sensors, and it controls many different idle speed parameters.

The Wax type and Bi-metal mechanical air valves are used only to regulate cold engine fast idle and are not ECU controlled.

There are some engines which utilize a mechanical air valve, for cold fast idle control, in combination with an ECU controlled ISC Vacuum Switching Valve (VSV) to control warm curb idle.

ENGINE CONTROLS PART #3 - IDLE SPEED CONTROL


Four Different ECU ModulatedIdle Speed Control Systems (ISC)

There are four different types of ECU con-trolled ISC systems used on Toyota engines. These systems are referred to as:

• Stepper motor type

• Rotary solenoid type

• Duty control ACV type

• On-off control VSV type

Step Motor Type ISC ValveThe Step Motor type ISCV is located on the intake air chamber or throttle body. It regulates engine speed by means of a stepper motor and pintle valve which controls the volume of air by-passing the closed throttle valve. The ISCV throttle air by-pass circuit routes intake air past the throttle valve directly to the intake manifold through a variable opening between the pintle valve and its seat.

The valve assembly consists of four electrical stator coils, a magnetic rotor, a valve and valve shaft. The valve shaft is screwed into the rotor so that as the rotor turns, the valve assembly will extend and retract.



The ECU controls movement of the pintle valve by sequentially grounding the four electrical stator coils. Each time current is pulsed through the stator coils, the shaft moves one 44 step." Direction of rotation is reversed by reversing the order with which current is passed through the stator coils.

The pintle valve has 125 possible positions, from fully retracted (maximum air by-pass) to fully extended (no air by-pass). In the event that the ISCV becomes disconnected or inoperative, its position will become fixed at the step count where it failed. Because the stepper idle speed control motor is capable of controlling large volumes of air, it is used for cold fast idle control and is not used in combination with a mechanical air valve.



Primary Controlled Parameters

Initial Set-upEngines equipped with the stepper type ISCV use an ECU controlled EFI main relay which delays system power down for about two seconds after the ignition is turned off. During these two seconds, the ECU fully opens the ISCV to 125 steps from seat, improving engine stability when it is started. This reset also allows the ECU to keep track of the ISCV position after each engine restart.

Engine Starting Control When the engine is started, rpm increases rapidly because the ISCV is fully open. This ISCV position is represented by point A on the graph, 125 steps from seat.

When 500 rpm is reached, the ECU drives the ISCV to a precise number of steps from seat based on the coolant temperature at time of start-up. This information is stored in a look up table in the ECU memory and is represented by point B on the graph.

Engine Warm-up ControlAs the engine coolant approaches normal operating temperature, the need for cold fast idle is gradually eliminated. The ECU gradually steps the ISCV toward its seat during warmup. The warm curb idle position is represented by point C on the graph. By

the time the coolant temperature reaches 176'F (80'C), the cold fast idle program has ended.

Feedback Idle Speed ControlThe ECU has a pre-programmed target idle speed which is maintained by the ISCV based on feedback from the Ne signal. Feedback idle speed control occurs any time the throttle is closed and the engine is at normal operating temperature. The target idle speed is programmed in an ECU look up table and varies depending on inputs from the A/C and NSW signals. Any time actual speed varies by greater than 20 rpm from target idle speed, the ECU will adjust the ISC valve position to bring idle speed back on target.



Engine Load/Speed ChangeEstimate ControlTo prevent major loads from changing engine speed significantly, the ECU monitors signals from the Neutral Start Switch (NSW) and the Air Conditioner switch (A/C) and re-establishes target idle speeds accordingly. ISCV position is adjusted very quickly as the status of the A/C or NSW inputs change. Before a change in engine speed can occur, the ECU has moved the ISCV to compensate for the change in engine load. This feature helps to maintain a stable idle speed under changing load conditions.

The following chart shows typical target idle speeds which can be found in New Car Feature books. These speed specifications can be useful when troubleshooting suspected operational problems in the step type idle speed control system or related input sensor circuits.

Other Controlled Parameters

Electrical Load Idle-upWhenever a drop in voltage is sensed at the ECU +B or IG S/W terminals, the ECU responds by increasing engine idle speed. This strategy ensures adequate alternator rpm to maintain system voltage at safe operational levels.

Deceleration Dashpot ControlSome ECUs use a deceleration dashpot function to allow the engine to gradually idle down. This strategy helps improve emissions control by allowing more air into the intake manifold on deceleration. This extra air is available to mix with any fuel which may have evaporated during the low manifold pressure conditions of deceleration.

Learned Idle Speed ControlThe idle speed control program is based on an ECU stored look up table which lists pintle step positions in relation to specific engine rpm values. Over time, engine wear and other variations tend to change these relationships. Because this system is capable of feedback control, it is also capable of memorizing changes in the relationship of step position and engine rpm. The ECU periodically rewrites the look up table to provide more rapid and accurate response to changes in engine rpm.



The Rotary Solenoid ISCV is mounted to the throttle body. This small, lightweight and highly reliable valve controls the volume of intake air which is allowed to by-pass the closed throttle valve. Air volume control is accomplished by means of a movable rotary valve which blocks or exposes the air by-pass port based on signals received from the ECU.

Because the Rotary Solenoid ISCV has large air volume capability, it is used to control cold fast idle as well as other idle speed parameters. Although this ISCV is not used in combination with a mechanical air valve, models equipped with air conditioning do require the use of a separate A/C idle-up device.

The valve assembly consists of two electrical coils, a permanent magnet, a valve and valve shaft. A fail-safe bi-metallic coil is fitted to the end of the shaft to operate the valve in the event of electrical failure in the ISCV system.



The ECU controls movement of the valve by applying a 250 Hz duty cycle to coils T1 and T2. The electronic circuitry in the ECU is designed to cause current to flow alternately in coil T1 when the duty cycle signal is low and in coil T2 when the signal is high. By varying the the duty ratio (on time compared to off time), the change in magnetic field causes the valve shaft to rotate.

As duty ratio exceeds 50%, the valve shaft moves in a direction that opens the air by-pass passage. At a duty ratio less than 50%, the shaft moves in a direction which closes the passage. If the electrical connector is disconnected or the valve fails electrically, the shaft will rotate to a position which balances the magnetic force of the permanent magnet with the iron core of the coils. This default rpm will be around 1000 to 1200 rpm once the engine has reached normal operating temperature.

Rotary ISCV Controlled Parameters

Engine Starling, Warm-upand Feedback Control When the engine is started, the ECU opens the ISCV to a pre-programmed position based on coolant temperature and sensed rpm. The higher the commanded rpm, the longer the duty ratio will be. As the engine approaches normal operating temperature, engine speed is gradually reduced.

Once the engine is fully warmed up, the ECU utilizes a feedback idle speed control strategy which functions identically with the stepper motor ISC system. Different target idle speeds are established depending on the status of load sensor inputs.

Turbo Charger Idle Down ControlOn the 3S-GTE engine, the ISCV remains at a higher idle air by-pass rate for a short period of time after high speed or heavy load operation. This strategy prevents damage to the turbocharger center shaft bearings by maintaining an elevated engine oil pressure.

All other controlled parameters for the Rotary Solenoid ISC system are the same as the with the Stepper type ISCV. Idle load stabilization is maintained when input from the neutral safety switch (NSW), headlights or rear window defogger (ELS) indicate additional engine load.

As with the Stepper type ISC system, the Rotary Solenoid system utilizes a learned idle speed control strategy. The ECU memorizes the relationship between engine rpm and duty cycle ratio and periodically updates its look up tables. Both systems utilize current supplied by the BATT terminal of the ECU to retain this learned memory. If the battery is disconnected, the ECU must relearn target step positions and duty cycle ratios.



Duty Control Air Control Valve (ACV) ISC

The Duty Control ACV is typically mounted on the intake manifold. It regulates the volume of air by-passing the closed throttle valve by opening and closing an air by-pass. Valve opening time is a function of a duty cycle signal received from the ECU.

The ACV is incapable of flowing large volumes of air; therefore, a separate mechanical air valve is used for cold fast idle on engines equipped with this system.

The Duty Control ACV consists of an electrical solenoid and a normally closed (N/C) valve which blocks passage of fresh air from the air cleaner to the intake manifold. The ECU controls the valve by applying a 10 Hz variable duty ratio to the solenoid, causing the valve to pass varying amounts of air into the manifold. By increasing the duty ratio, the ECU holds the air by-pass circuit open longer, causing an increase in idle speed.

Duty Control ACV Controlled Parameters

Starting and Warm Curb IdleWhen the STA signal to the ECU is on, the ECU cycles the VSV at a 100% duty cycle to improve startability. The ACV does not have any effect on cold fast idle or warm-up fast idle speed.



When the engine has reached normal operating temperature, and the IDL contact is closed, the ECU uses a feedback idle speed control strategy to control warm curb idle speed. When loads are applied to the engine from the automatic transmission or electrical devices, the ECU adjusts target idle speeds accordingly. When the IDL contact is open or any time the Air Conditioning (A/C) signal to the ECU is on, the ECU maintains a constant duty cycle ratio to the ACV, allowing a fixed amount of by-pass air to flow.

Diagnostic ModeWhen the TCCS system enters diagnostic mode (TE1 shorted to E1), the ECU will drive the ACV to a fixed duty cycle ratio regardless of engine operating conditions. Curb idle adjustment on engines equipped with this ISC system is performed in diagnostic mode. For more information on curb idle adjustment procedures, refer to Appendix C.

On-Off Control Vacuum SwitchingValve (V-ISC System)The simple On-Off Vacuum Switching Valve (VSV) ISC system is controlled by signals from the ECU or directly by tail lamp and rear window defogger circuits. The Vacuum Switching Valve (VSV) is typically located on the engine (often under the intake manifold) or in the engine compartment, controlling a fixed air bleed into the intake manifold.

The valve is a normally closed (N/Q design which is opened when current is passed through the solenoid windings. Unlike most ECU controlled circuits which are ground circuit driven, the ECU controls this VSV by supplying current to the solenoid coil when pre-programmed conditions are met. Additionally, current can be supplied to the solenoid from the rear window defogger or taillight circuits by passing through isolation diodes.



The VSV allows only a small amount of air to by-pass the closed throttle valve when it is open, increasing engine speed by about 100 rpm when energized. This ISC system does not control cold fast idle, and engines equipped with the system use a mechanical air valve for cold engine fast idle.

On-Off Control VSV Controlled Parameters

Engine Starting and Warm Curb Idle Control The solenoid is energized by the ECU whenever the STA signal is on and for a short period of time thereafter to improve startability. Additionally, when the IDL contact is closed, the ECU will energize the solenoid whenever engine speed drops below a pre-determined rpm.

Automatic Transmission Idle-up ControlThe ECU will energize the VSV for several seconds after shifting the transmission from Park or Neutral to any other gear to stabilize engine speed during the transition from unloaded to loaded conditions.

Electrical Load Idle-upReferring to the electrical schematic, the VSV receives current directly from the tail lamp and rear window defogger circuits through isolation diodes whenever these circuits are operating.

Diagnostic ModeWhenever the TE1 circuit is grounded, the ECU is prevented from actuating the V-ISC Vacuum Switching Valve. This inhibit feature is useful during diagnostic and other service procedures. It is important to note that this will not prevent the VSV from energizing when the defogger or tail lamp relays are energized.



Input Sensors Affecting IdleSpeed Control Output

Major Impact Sensors

The following input signals to the ECU have a major impact on the output commands sent to the Idle Speed Control Valve.

Engine RPM (Ne)The Ne signal is one of the most critical inputs for proper operation of the ISC system. This sensor supplies the engine rpm feedback used to determine whether actual rpm equals target rpm.

Throttle Position (IDL)The Idle Speed Control System is functional only when the throttle is closed and the vehicle is not moving. The ECU monitors the IDL signal to determine when to output commands to the ISC actuator. When the IDL contact is closed and the vehicle is not moving, the ECU outputs signals to the ISCV. When the IDL contact is open, the ISC system is not functional. Without an accurate signal from the IDL contact, the ISC system cannot function normally.

Engine Coolant Temperature (THW)The idle speed control program look up tables list different engine rpm targets depending on coolant temperature for the Step and Rotary ISC systems which control cold fast idle. The ECU uses the THW signal to determine engine coolant temperature for accurate control of idle speed under all engine temperature conditions.

Vehicle Speed (SPD)The ISC system is not functional when the vehicle is moving. The ECU monitors the SPD signal from the vehicle speed sensor to determine when to operate the ISCV. If the IDL contact is closed and no SPD signal is detected, the ECU will output a signal to the ISCV.

Vehicle Speed Sensor OperationThe ECU expects to see a digital signal of four pulses for each speedometer cable revolution when the vehicle is moving. The vehicle speed sensor (VSS) provides this signal.

There are two different types of vehicle speed sensors used to supply information to the engine ECU. Although these sensors differ in design, the final output signal to the ECU is the same for both, four digital pulses per cable revolution.

Reed Switch Type: The Reed Switch vehicle speed sensor is located in the combination meter assembly and is operated by the speedometer cable. The sensor consists of an electrical reed switch and a multiple pole permanent magnet. As the the speedometer cable turns, the permanent magnet rotates past the reed switch. The magnetic flux lines cause the contacts to open and close as they pass. The magnet is arranged so that the sensor contacts open and close four times for each revolution of the sensor.



Photocoupler Type: The Photocoupler vehicle speed sensor is also located in the combination meter and operated by the speedometer cable. The sensor consists of a photocoupler circuit and a 20-slot trigger wheel.

The photocoupler circuit is a simple electronic device which uses a photo-transistor and a light emitting diode (LED) to generate a digital electrical signal (see article on Karman vortex air flow meter in Chapter 5 for operation theory of photocoupler circuit). As the slotted trigger wheel moves between the LED and phototransistor, it intermittently blocks and passes light at the photo-transistor. When the wheel blocks the LED, the transistor turns off and when the wheel passes the light, the transistor turns on.

With 20 slots, this sensor generates 20 digital pulses per speedometer revolution. An electronic circuit in the combination meter conditions this signal into four pulses which are sensed by the SPD circuit in the ECU.

Electrically, both the Reed type and Photocoupler type speed sensors work the same. The sensor is, in fact, a switch. By switching on and off, the sensor pulls a reference voltage from the ECU to ground. The resulting voltage drop is monitored by the ECU as the SPD signal.



Minor Impact Sensors

Neutral Start Switch (NSW)The Neutral Start Switch input to the ECU is used for ISC control as well as having an influence, although minor, on the fuel delivery program. As it relates to the ISC system, this input is used to determine when to increase idle speed for Engine Load/Speed Change Estimate strategy.

The NSW signal at the ECU will be low (less than 1 volt) as long as the neutral start switch is closed, as it will be with the gear selector in Park or Neutral. This low signal is caused by the voltage drop across R1 which has a relatively high resistance compared to the starter and circuit opening relay coils. When the transmission is shifted into any gear, the neutral start switch opens, causing a halt in current flow through the NSW circuit. This causes an increase in signal voltage at the NSW terminal of the ECU.

In the event this signal malfunctions, the ECU will use the wrong target idle speed for in gear operation and a distinct drop in idle rpm will be noticed as the transmission is shifted from Park or Neutral to any drive gear.

Engine Cranking Signal (STA)The STA signal is used by the ECU to allow additional air to enter the intake manifold while cranking the engine. Additionally, it is used to determine when to enrich injection for starting and when to operate the Fuel Pressure-Up (FPU) system. In the event that the STA signal malfunctions, the engine may be difficult to start.

The STA signal at the ECU will be low at all times except while the engine is cranking. While cranking, the STA signal goes high (cranking voltage) as current flows through the closed ignition switch and neutral start switch contacts.



Air Conditioning Compressor Signal (A/C) The A/C signal to the ECU is used to determine when the air conditioning compressor is loading the engine. The signal is used primarily as an indication to increase ISC air flow to stabilize idle speed. The A/C input is also used by the ECU to modify ignition timing and deceleration fuel cut parameters during compressor operation periods. When the A/C signal is high and the IDL contact is closed, the ECU limits minimum ignition spark advance angle. Additionally, decel fuel cut rpm is increased. In the event that this signal malfunctions, idle quality may suffer and driveability during deceleration could be affected.

The A/C signal at the ECU will be high any time the compressor clutch is energized. When power is removed from the clutch circuit, it is simultaneously removed from the A/C input at the ECU.

Electrical Load Sensor (ELS)The ELS circuit signals the ECU when significant electrical load has been placed on the charging system from the vehicle lighting or rear window defogger systems. The ECU uses this information to increase the duty cycle ratio on the Rotary ISC Valve, thereby maintaining a stable idle speed.

The ELS signal at the ECU will be low as long as the tail lamps and rear window defogger are off. When either of these accessories are turned on, current flows to the accessory and through an isolation diode to the ECU. When either accessory is on, the signal at the ECU will go to battery voltage.



System Diagnosis and Troubleshooting

An Overview of the Self Diagnostic System The ECU on all P7 and TCCS engines has a self diagnostic system which constantly monitors most of the electronic control system's input circuits. When the ECU detects a problem, it can turn on the check engine light to alert the driver that a fault exists in the system. At the same time, the ECU registers a diagnostic code in its keep alive memory so that the faulty circuit can be identified by a service technician at a later time.

if the circuit fault goes away, the check engine light will go off. However, the diagnostic code will remain in the ECU memory even after the ignition switch is turned off. For most engines, the contents of the diagnostic memory can be checked by shorting check connector terminals T (or TE1) and E1 together and counting the number of flashes on the check engine light.

After the problem has been repaired, the technician can clear the diagnostic system by removing the power from the ECU BATT feed.

Fault Detection PrinciplesThe ECU fault detection system is programmed to accept sensor signal values within a certain range to be normal, and signals outside of that range to be abnormal. The normal signal range used to diagnose most sensor circuits covers the entire operating range of the sensor signal. As long as the signal value falls within this range, the ECU judges it to be normal. As a result, it is possible for the sensor to generate a signal which does not accurately represent the actual operating condition and not be detected as a problem by the ECU.

The fault detection range graph shows typical THW signal parameters. Point A is normal operating temperature and falls within the fault detection normal range. Point B represents the freezing point of water and also falls in the normal range. If the engine is at normal operating temperature but the THW sensor signals the ECU that the coolant temperature is freezing (point B), the engine will operate excessively rich and may not start when hot. Because point B falls within the normal range, the ECU will not recognize this as a problem. No diagnostic code will be set for this problem.

Limitations of the Self Diagnostic System The self diagnostic system provides an excellent routine to direct the technician to the heart of an electronic control system problem. There are however, several limitations which must be kept in mind when troubleshooting.

• The ECU must see a signal in an abnormal range for more than a given amount of time before it will judge that signal to be faulty. Therefore, many intermittent problems cannot be detected by the ECU.

ENGINE CONTROLS PART #4 - DIAGNOSIS


• When the ECU stores a diagnostic code, the code indicates a problem somewhere in the sensor circuit, not necessarily in the sensor itself Further testing is always required to properly diagnose the circuit.

• Not all circuits are monitored by the ECU. Just because the ECU generates a normal code does not mean that there are no problems within the electronic control system.

• Occasionally, diagnostic codes can be set during routine service procedures or by problems outside the electronic control system. Always clear codes and confirm that they reset prior to circuit troubleshooting.

Check Engine Lamp FunctionsThe check engine lamp serves two functions in the self diagnostic system, depending on the status of the T terminal. When the T terminal is off (not shorted to E1) the check engine light goes on to warn the driver when a major problem is detected in the electronic control system. When the T terminal is on (shorted to E1) the check engine light displays stored diagnostic codes for use by the technician.

VF (Voltage Feedback)Terminal Function The VF terminal also serves two diagnostic functions depending on the status of the T terminal. When the T terminal is off, the VF terminal voltage represents learned value correction factor. When the T terminal is on, the VF terminal will either display an emulated oxygen sensor signal (throttle open, IDL contact off) or indicate whether a diagnostic code is stored in the ECU memory (throttle closed, IDL contact on).



Four Systematic StepsIn DiagnosisSimply stated, there are four steps to follow when performing a methodical diagnosis from start to finish. Using this systematic approach will generally lead to reduced diagnostic time and a higher degree of success. The four steps are listed as follows.

• Routine Quick Checks• Use of the Self Diagnostic System• Troubleshooting by Symptom• Quality Control Check

Routine Quick ChecksThis step in diagnosis includes confirmation of the problem and routine mechanical and electrical engine checks.

Confirmation of the customer concern is an excellent place to begin any diagnosis. It is important to gather and analyze as much information as the customer can supply and, if the check engine warning lamp is on, to retrieve and record the diagnostic codes.

The conditions of the battery and charging system are critical to the proper operation of the electronic control system. Both should be routinely checked by measuring cranking and engine running battery voltage prior to proceeding with diagnosis.

Depending on the problem or driveability symptom indicated, the following checks should be conducted under the hood:

• Inspection of the engine's mechanical condition (i.e., audible cranking rhythm and visual ignition secondary condition).

• Brief inspection of accessible electrical, vacuum and air induction system duct connections.

• Locate and inspect the condition of the ECU main grounds.

• Inspect for leakage in the EGR and PCV valves. • Inspect for unwanted fuel entering the intake

manifold from the EVAP system.

The entire routine quick check procedure can be performed in less than ten minutes and will often save an hour or more of unnecessary diagnostic time.

Use of the Self Diagnostic System Once you are satisfied that there are no routine problems causing the customer concern, use of the self diagnostic system is in order. This system is available on all P7 and TCCS equipped engines and is capable of indicating if certain faults exist in ECU monitored circuits.

The P7 systems have limited diagnostic capabilities and can only display seven diagnostic codes, including a system normal code. This system will only indicate a fault if the circuit is open or shorted to ground.

Late model TCCS systems have more sophisticated diagnostics which monitor more ECU related circuits with as many as 21 or more diagnostic codes. The latest TCCS ECUs have some special capabilities which make them more useful in diagnosis and prevent the check engine warning light from becoming a source of customer dissatisfaction.

• To allow the diagnostic system to find more system faults, the electrical parameters which the ECU uses to set a diagnostic code are altered to find sensor performance faults like oxygen sensor degradation.

• Some minor TCCS system fault codes will set a diagnostic code in the ECU keep alive memory but will not turn on the check engine light and unnecessarily alarm the customer.

• To prevent false indication of certain system faults, some ECUs are programmed to use a two-trip detection logic which prevents the check engine light from illuminating, or certain codes from setting, until the problem has duplicated itself twice, with a key off cycle in between.

• Some ECUs have a special diagnostic TEST mode which causes the ECU to narrow its diagnostic parameters for the technician, thereby, making troubleshooting intermittent problems easier.



Procedures toRetrieve Trouble CodesThere are several different types and locations of diagnostic connectors which are used to trigger and, in some cases, read diagnostic code output from Toyota EFI engines. All late model TCCS applications, from 1988, use a multiple terminal diagnostic check connector. Earlier models use this same multiple terminal or a two-terminal check connector, all located under the hood.

The procedure to examine the ECU memory for diagnostic codes is typically very simple regardless of which vintage engine being diagnosed. All engines equipped with self diagnostic systems have one terminal of the check connector identified as T or TE1. When grounded, this terminal triggers the self diagnostic feature of the ECU. The E1 ground circuit is also located in the check connector.

To enter engine diagnostics:

• Locate the check connector under the hood and identify the T (TE1 on late model TCCS) and E1 terminals.

• Turn the ignition switch to the "on" position and make sure that the check engine light is on.

• Confirm that the throttle is closed (IDL contact on).

• Jumper check connector terminals T (TE1) to E1.



When the T terminal is grounded with the ignition switch in the "on" position, the ECU sees the voltage at terminal T go low. Low voltage on T causes the ECU to enter diagnostic mode, producing diagnostic codes on the check engine light. On '83 through '85 Cressida and Supra models, the check engine light does not flash diagnostic codes. An analog voltmeter must be used to read the codes from the VF terminal of the EFI Service Connector.

Depending on the vintage of the system being tested, the codes will be displayed in either one or two digit format. It is important to refer to the proper repair manual for specific information about diagnostic connector location, code format, and proper procedures for the vehicle you are troubleshooting.



Super Monitor Display: On some 1983 through 1987 Cressida and Supra models, a Super Monitor trip computer was offered as optional equipment. This display can be used to read diagnostic codes by simply pressing and holding the monitor "Select" and "Input M" keys together, for three seconds, with the ignition switch in the "on" position. When the "DIAG" message appears on the display, pressing and holding the "Set" key for three seconds will put the TCCS system into diagnostic mode. The display will indicate any diagnostic codes stored in the ECU's keep alive memory.

Once Diagnostic CodesAre RetrievedOnce diagnostic codes have been retrieved from the ECU keep alive memory, it is advisable to erase the codes and road test the vehicle. 'Me purpose of this procedure is to confirm that the problem(s) will be present during your diagnosis.

If the diagnostic code re-occurs, the problem can be considered a hard fault and troubleshooting will be routine. If the diagnosis code does not re-occur, the problem is either intermittent or was inadvertently stored during a previous service procedure.

If an intermittent fault is suspected, a physical check of the indicated circuit must be performed by flexing connectors and harnesses at likely failure points while monitoring the circuit with a multimeter or oscilloscope. If the problem is temperature, vibration, or moisture related, the circuit can be heated, lightly tapped, or sprayed with water to simulate the failure conditions. Attempting to troubleshoot intermittent problems using the normal diagnostic routines will likely result in a misdiagnosis and wasted time.

Erasing Long Term Memory The procedure to erase stored diagnostic codes is as simple as removing a fuse or disconnecting the battery negative terminal for at least thirty seconds. Fuse removal is the method of choice because it will not disturb any other computer memories in the vehicle (ETR radio stations, trip computer data, etc.)

The proper fuse to remove depends on application but will always be the one which feeds the ECU BATT terminal. The following fuses supply BATT power distribution to the ECU keep alive memory: EFI, STOP, or on some P7 applications, ECU +B.



Monitored andNon-monitored CircuitsAlthough the newer TCCS self diagnostic system is getting more sophisticated every model year, there are still many electronic control system circuits which the ECU does not monitor. Generally speaking, most input sensors are monitored for faults, but most output actuators are not. Exceptions to this are the Neutral Start Switch (NSW) and Power Switch (PSW)* input signals which are not monitored. Codes 25 and 26 monitor the air/fuel ratio rather than the status of a particular circuit.

Troubleshooting After Code RetrievalThe diagnostic code leads only to a circuit level diagnosis. A pinpoint test of the circuit indicated will be required to isolate the problem down to the component or wiring level.

To find the appropriate diagnostic procedure to follow:

• Refer to the last column of the repair manual "Diagnostic Codes" list.

• This will lead to one or more "Troubleshooting with a Voltmeter/Ohmmeter" diagnostic charts which will facilitate circuit diagnosis.

• This may also lead to an "Inspection of Component" procedure which will facilitate diagnosis of the sensor or actuator in the circuit.

But what if you do not have a diagnostic code to help lead you to the cause of the customer complaint? What do you do next? Before we address the third step in the systematic diagnostic approach, the subject of an inoperative self diagnostic system must be addressed.



No Self Diagnostic SystemOutput (Use of Diagnostic Circuit Inspection Schematic) There are several conditions which could cause the self diagnostic system to malfunction. In the event the check engine light does not work or if the system will not flash diagnostic codes, it will be impossible to make an accurate diagnosis of the electronic control system. Following are some suggestions to help troubleshoot this condition if it is encountered.

Normal OperationThe following sequence of events should occur when diagnostics are functioning normally: • With the ignition switch in the "on" position,

the check engine fight should be on steady. • When the T circuit is grounded, the check

engine light should flash a normal code if all monitored circuits are in proper working order.

• If a fault exists in any monitored circuit, the appropriate diagnostic code should be displayed. If there is more than one code stored in the ECU keep alive memory, codes will be displayed in numerical sequence from lowest to highest.

• Diagnostic codes will continue to repeat until the key is turned off or the T circuit ground is removed.

Abnormal OperationIn the event the self diagnostic system is not functioning normally, it will likely exhibit one of the following symptoms.

1) Check engine light fails to come on at power up (key on, engine off, T circuit open).

2) Check engine light will not flash code when T circuit grounded (T jumpered to E1), check engine lamp stays on or stays off.

These conditions must be corrected before further diagnosis can be performed! The following charts will help to direct you to perform a "Diagnostic Circuit Inspection."



At this stage in your diagnosis, you may have already diagnosed the problem and are ready for repair and a quality control check. If the problem has not yet been identified, you are ready for the next diagnostic step.

Troubleshooting By SymptomWhen the self diagnostic system fails to indicate a problem with the electronic control system (normal code displayed), there are two possibilities left. Either there is a problem in the electronic control system which the ECU is not capable of detecting or the problem lies outside of the electronic control system entirely. In either case, the "Troubleshooting" section of the repair manual will help you locate the appropriate diagnostic routine to quickly isolate the problem cause.

The third step in a systematic diagnosis requires use of the "Troubleshooting" and cc Voltage at ECU Wiring Connectors" sections of the repair manual. Based on the symptom the vehicle exhibits, these manual sections will lead you to the diagnostic routine which will assist in solving the problem.

Voltage at ECU Connector ChecksThe self diagnostic system is not capable of detecting sensor circuits which are feeding out of range information to the ECU. By using the Voltage at ECU Wiring Connectors chart, measured voltage signals at the ECU can be compared to standard voltage values listed

in the repair manual. Signals which are out of the normal range can be identified and the cause diagnosed by referring to the far right column of the chart; this will lead to the appropriate pinpoint test to perform.

In the event that all listed values fall within a normal range, the symptom charts in the repair manual should be consulted. Starting with new models introduced after '90, repair manuals include a comprehensive troubleshooting matrix that replaces the symptoms charts. Beginning with '92 repair manuals, this matrix is located at the beginning of the Emissions (EM) section of the repair manual.

Using the Symptom Chartsand Troubleshooting Matrix The most important part of troubleshooting by symptom is to identify the symptom accurately. An accurate description of the problem will ensure that the appropriate diagnostic routines will be selected. Based on the symptom chosen, a series of testing routines are available to assist in pinpointing the problem area.

These test routines address items within the electronic control system as well as areas outside the system which could cause the symptom chosen. The technician's knowledge and experience will be his guide to which tests to perform first and which tests to disregard in any particular situation.



Quality Control Check andConfirmation of Closed LoopThe final step in any diagnosis and repair is a quality control check to confirm that the original customer complaint has been corrected and that the system is functioning normally. In the case of the engine electronic control system, the Quality Control Check should consist of the following items:

• Clear any stored diagnostic codes.

• Confirm closed loop operation.

• Confirm normal air/fuel ratio calibration.

• Confirm codes do not reset.

Three of these confirmations can be performed using the VF terminal of the check connector.

Using the VF Terminal As A Closed Loop and Air/Fuel Ratio MonitorThe VF terminal serves as a closed loop monitor, allowing the technician to track the oxygen sensor activity and confirm closed loop operation.

To Use the VF Terminal as aClosed Loop Monitor

• T terminal must be on (shorted to E1).

• IDL contacts must be off (throttle open).

When these conditions have been satisfied, the voltage signal on the VF terminal will imitate the oxygen sensor signal. Whenever the oxygen sensor signal is high, indicating a rich exhaust condition, the VF terminal voltage will be 5 volts. When the oxygen sensor signal is low, indicating a lean exhaust condition, the VF terminal voltage will be 0 volts.

At 2500 rpm, oxygen sensor switching should occur a minimum of eight times in ten seconds if the closed loop system is operating normally. To test, the engine must be fully warmed up and run at 2500 rpm for one minute to ensure the oxygen sensor has reached operating temperature.



To Use the VF Terminal toConfirm Air/Fuel Ratio

• T terminal must be off (not grounded).

Under this condition, the VF voltage represents the learned value correction factor to fuel injection duration. As you learned in Chapter 5, final injection duration is the sum of basic injection plus injection corrections. Learned value is simply another correction factor which is used to bring the corrected air/fuel ratio as close to the stoichiometric air/fuel ratio as possible.

The ECU fuel injection duration program is the same for every engine; however, each engine is a little bit different from the next. The purpose of the learned value correction is to tailor the standard fuel injection duration program to each individual engine. The injection duration calculation, before oxygen sensor correction, is the ECU's best guess at a stoichiometric air/fuel ratio. The oxygen sensor correction fine-tunes injection duration precisely to 14.7 to 1. The learned value correction factor ensures that oxygen sensor corrections do not become too large to manage.

In this mode, the VF voltage signal will be at one of five different steps (three steps on D type EFI) depending on how close the calculated air/fuel ratio (before oxygen sensor correction) is to stoichiometry. With the engine operating in closed loop, learned value VF should be somewhere in the 1.25 to 3.75 volt range with a nominal value of 2.5 volts.

Generally speaking, a lower voltage indicates the ECU is decreasing fuel to correct for some long term rich condition. Examples of conditions which could cause low learned value VF:

• Crankcase diluted with fuel

• Loaded evaporative canister

• High fuel pressure

A higher voltage indicates that the ECU is increasing fuel to correct for some long term lean condition. Examples of conditions which could cause high learned value VF:

• Atmospheric leaks into intake system

• Worn throttle shaft

• Low fuel pressure



Toyota DiagnosticCommunications Link (TDCL) The TDCL is an enhanced diagnostic check connector which adds a special diagnostic TEST mode to the self diagnostic system. It is only used on '89 and later Cressida, '92 and later Camry, and all Lexus models. It is located under the left side of the instrument panel.

The TDCL uses a TE2 test terminal, which when grounded, triggers the special TEST mode. In TEST mode, the ECU is capable of detecting intermittent electrical faults which are difficult to detect in a normal diagnostic mode. The ECU eliminates most code setting conditions when TEST mode is entered, allowing it to immediately detect a malfunction in many of the monitored circuits. Using the DiagnosticTEST Mode ProcedureWith the ignition switch off, connect terminals TE2 and E1 using SST #09842-18020 (TEST mode will not start if TE2 is grounded after the ignition switch is already on).

• Turn the ignition switch on; then start the engine and drive the vehicle at least 6 mph or higher (code 42, vehicle speed sensor will set if vehicle speed does not exceed 6 mph).

• Simulate driving conditions that problem occurs under.

• When the check engine lamp comes on, jumper TE1 to El without disconnecting TE2.

• Note and record diagnostic codes (codes display in same manner as in normal diagnostic mode).

• Exit diagnostic TEST mode by disconnecting TE2 and turning the ignition switch off.

Diagnostic TEST mode is also available on the > '92 Celica 5S-FE and 3S-GTE applications through the check connector TE2 terminal. For more information on using the VF terminal and the TE2 TEST mode diagnostics, refer to Course #872, TCCS Diagnosis.



Position/Mode Sensors and SwitchesFor many components, it is important that the ECM know the position and/or mode of the component. A switch is used as a sensor to indicate a position or mode. The switch may be on the supply side or the ground side of a circuit.

Power Side Switch CircuitA power side switch is a switch located between the power supply and load. Sometimes the power side switch is called hot side switch because it is located on the hot side, that is, before the load, in a circuit. The Stop Lamp switch is a good example. When the brake pedal is depressed, the Stop Lamp switch closes sending battery voltage to the ECM. This signals the ECM that the vehicle is braking.

MODE SENSORS AND SWITCHES


The following switches act as switches for the ECM. Usually, they are supply side switches. Note in the figure(s) their location between the battery and ECM. Many switches that commonly use battery voltage as the source are:

• Ignition Switch.

• Park/Neutral Switch.

• Transfer Low Position Detection Switch.

• Transfer Neutral Position Detection Switch.

• Transfer 4V;D Detection Switch.



Ground Side Switch CircuitA ground side switch is located between the load and ground in a circuit. Inside the ECM there is resistor (load) connected in series to the switch. The ECM measures the available voltage between the resistor and switch. When the switch is open, the ECM reads supply voltage. When the switch is closed, voltage is nearly zero.

The following switches are typically found on the ground side of the circuit:

• TPS Idle Contact (IDL signal) The TPS Idle Contact Switch uses a 12 volt reference voltage from the ECM.

• Power Steering Pressure Switch.

• Overdrive Switch.



Temperature SensorsThe ECM needs to adjust a variety of systems based on temperatures. It is critical for proper operation of these systems that the engine reach operating temperature and the temperature is accurately signaled to the ECM. For example, for the proper amount of fuel to be injected the ECM must know the correct engine temperature. Temperature sensors measure Engine Coolant Temperature (ECT), Intake Air Temperature (IAT) and Exhaust Recirculation Gases (EGR), etc.

TEMPERATURE SENSORS


Engine Coolant Temperature (ECT) SensorThe ECT responds to change in Engine Coolant Temperature. By measuring engine coolant temperature, the ECM knows the average temperature of the engine. The ECT is usually located in a coolant passage just before the thermostat. The ECT is connected to the THW terminal on the ECM.

The ECT sensor is critical to many ECM functions such as fuel injection, ignition timing, variable valve timing, transmission shifting, etc. Always check to see if the engine is at operating temperature and that the ECT is accurately reporting the temperature to the ECM.

Intake Air Temperature (IAT) SensorThe IAT detects the temperature of the incoming air stream. On vehicles equipped with a MAP sensor, the IAT is located in an intake air passage. On Mass Air Flow sensor equipped vehicles, the IAT is part of the MAF sensor. The IAT is connected to the THA terminal on the ECM. The IAT is used for detecting ambient temperature on a cold start and intake air temperature as the engine heats up the incoming air.

NOTE: One strategy the ECM uses to determine a cold engine start is by comparing the ECT and IAT signals. If both are within 8'C (15'F) of each other, the ECM assumes it is a cold start. This strategy is important because some diagnostic monitors, such as the EVAP monitor, are based on a cold start.

TEMPERATURE SENSORS


Exhaust Gas Recirculation (EGR) Temperature SensorThe EGR Temperature Sensor is located in the EGR passage and measures the temperature of the exhaust gases. The EGR Temp sensor is connected to the THG terminal on the ECM. When the EGR valve opens, temperature increases. From the increase in temperature, the ECM knows the EGR valve is open and that exhaust gases are flowing.

TEMPERATURE SENSORS


ECT, IAT, & EGR Temperature Sensor OperationThough these sensors are measuring different things, they all operate in the same way. From the voltage signal of the temperature sensor, the ECM knows the temperature. As the temperature of the sensor heats up, the voltage signal decreases. The decrease in the voltage signal is caused by the decrease in resistance. The change in resistance causes the voltage signal to drop.

The temperature sensor is connected in series to a fixed value resistor. The ECM supplies 5 volts to the circuit and measures the change in voltage between the fixed value resistor and the temperature sensor.

When the sensor is cold, the resistance of the sensor is high, and the voltage signal is high. As the sensor warms up, the resistance drops and voltage signal decreases. From the voltage signal, the ECM can determine the temperature of the coolant, intake air, or exhaust gas temperature.

The ground wire of the temperature sensors is always at the ECU usually terminal E2. These sensors are classified as thermistors.

Temperature Sensor DiagnosticsTemperature sensor circuits are tested for:

• opens. • shorts. • available voltage. • sensor resistance.

The Diagnostic Tester data list can reveal the type of problem. An open circuit (high resistance) will read the coldest temperature possible. A shorted circuit (low resistance) will read the highest temperature possible. The diagnostic procedure purpose is to isolate and identify the temperature sensor from the circuit and ECM.

High resistance in the temperature circuit will cause the ECM to think that the temperature is colder than it really is. For example, as the engine warms up, ECT resistance decreases, but unwanted extra resistance in the circuit will produce a higher voltage drop signal. This will most likely be noticed when the engine has reached operating temperatures. Note that at the upper end of the temperature/resistance scale, ECT resistance changes very little. Extra resistance in the higher temperature can cause the ECM to think the engine is approximately 20'F = 30'F colder than actual temperature. This will cause poor engine performance, fuel economy, and possibly engine overheating.

TEMPERATURE SENSORS


Solving Open Circuit ProblemsA jumper wire and Diagnostic Tester are used to locate the problem in an open circuit.

TEMPERATURE SENSORS


Solving Shorted Circuit ProblemsCreating an open circuit at different points in the temperature circuit will isolate the short. The temperature reading should go extremely low (cold) when an open is created.

TEMPERATURE SENSORS


ASSIGNMENT NAME: ___________________________

1. List the three types of temperature sensors used and explain the function of each?

2. Temperature sensors are actually ______________?

3. Draw a sample temperature sensor circuit. (Label all parts)

4. The ECT us used by the computer to control what functions?

5. What PCM strategy is used when both the IAT and ECT are within 15’F of each other?

6. Temperature sensors are tested for:

7. Describe the procedure of testing a temperature sensor.

TEMPERATURE SENSORS


Position SensorsIn many applications, the ECM needs to know the position of mechanical components. The Throttle Position Sensor (TPS) indicates position of the throttle valve. Accelerator Pedal Position (APP) sensor indicates position of the accelerator pedal. Exhaust Gas Valve (EGR) Valve Position Sensor indicates position of the EGR Valve. The vane air flow meter uses this principle.

Electrically, these sensors operate the same way. A wiper arm inside the sensor is mechanically connected to a moving part, such as a valve or vane. As the part moves, the wiper arm also moves. The wiper arm is also in contact with a resistor. As the wiper arm moves on the resistor, the signal voltage output changes. At the point of contact the available voltage is the signal voltage and this indicates position. The closer the wiper arm gets to VC voltage, the higher the signal voltage output. From this voltage, the ECM is able to determine the position of a component.

POSITION SENSORS


Throttle Position SensorThe TPS is mounted on the throttle body and converts the throttle valve angle into an electrical signal. As the throttle opens, the signal voltage increases.

The ECM uses throttle valve position information to know:

• engine mode: idle, part throttle, wide open throttle.

• switch off AC and emission controls at Wide Open Throttle (WOT).

• air-fuel ratio correction.

• power increase correction.

• fuel cut control.

The basic TPS requires three wires. Five volts are supplied to the TPS from the VC terminal of the ECM. The TPS voltage signal is supplied to the VTA terminal. A ground wire from the TPS to the E2 terminal of the ECM completes the circuit.

At idle, voltage is approximately 0.6 - 0.9 volts on the signal wire. From this voltage, the ECM knows the throttle plate is closed. At wide open throttle, signal voltage is approximately 3.5 - 4.7 volts.

Inside the TPS is a resistor and a wiper arm. The arm is always contacting the resistor. At the point of contact, the available voltage is the signal voltage and this indicates throttle valve position. At idle, the resistance between the VC (or VCC terminal and VTA terminal is high, therefore, the available voltage is approximately 0.6 - 0.9 volts. As the contact arm moves closer the VC terminal (the 5 volt power voltage), resistance decreases and the voltage signal increases.

POSITION SENSORS


Some TPS incorporate a Closed Throttle Position switch (also called an idle contact switch). This switch is closed when the throttle valve is closed. At this point, the ECM measures 0 volts and there is 0 volts at the IDL terminal. When the throttle is opened, the switch opens and the ECM reads +B voltage at the IDL circuit.

POSITION SENSORS


The TPS on the ETCS-i system has two contact arms and to resistors in one housing. The first signal line is VTA1 and the second signal line is VTA2.

VTA2 works the same, but starts at a higher voltage output and the voltage change rate is different from VTA1 As the throttle opens the two voltage signals increase at a different rate. The ECM uses both signals to detect the change in throttle valve position. By having two sensors, ECM can compare the voltages and detect problems.

POSITION SENSORS


Accelerator Pedal Position (APP) SensorThe APP sensor is mounted on the throttle body of the ETCS-i. The APP sensor converts the accelerator pedal movement and position into two electrical signals. Electrically, the APP is identical in operation to the TPS.

EGR Valve Position SensorThe EGR Valve Position Sensor is mounted on the EGR valve and detects the height of the EGR valve. The ECM uses this signal to control EGR valve height. The EGR Valve Position Sensor converts the movement and position of the EGR valve into an electrical signal. Operation is identical to the TPS except that the signal arm is moved by the EGR valve.

Position Sensor DiagnosticsThe following explanations are to help you with the diagnostic procedures in the Repair Manual. The explanations below are representative to the order listed in the RM. You may find different orders in the RM.

Diagnostic TesterComparing the position of the sensor to Diagnostic Tester data is a convenient way of observing sensor operation. For example, with the TPS, the lowest percentage measured with Key On/Engine Off is with the throttle valve at its minimum setting, and the highest percentage will be at Wide Open Throttle.

POSITION SENSORS


Inspect Throttle Position SensorOn some models, you will find TPS checks in the Throttle Body on Vehicle Inspection in the SF Section.

POSITION SENSORS


POSITION SENSORS


ASSIGNMENT NAME: ___________________________

1. What are some of the common uses of position sensors? List them.

2. Explain how a position sensor (potentiometer) works?

3. Draw a sample position sensor circuit. Label all parts.

4. The PCM (ECM) uses throttle valve position information to control what functions?

5. Why do some TPS have an IDL contact and how does the PCM use this information?

6. What are the typical voltage values of a TPS? (Reference, idle, WOT)

7. Why does the PCM use an EGR position sensor and how is it used? Explain the strategy behind this sensor.

8. Explain the testing procedure for a position sensor such as a TPS. (In detail)

POSITION SENSORS


Mass Air Flow (MAF) SensorsThe Mass Air Flow Sensors converts the amount of air drawn into the engine into a voltage signal. The ECM needs to know intake air volume to calculate engine load. This is necessary to determine how much fuel to inject, when to ignite the cylinder, and when to shift the transmission. The air flow sensor is located directly in the intake air stream, between the air cleaner and throttle body where it can measure incoming air.

There are different types of Mass Air Flow sensors. The vane air flow meter and Karmen vortex are two older styles of air flow sensors and they can be identified by their shape. The newer, and more common is the Mass Air Flow (MAF) sensor.

Mass Air Flow Sensor: Hot Wire TypeThe primary components of the MAF sensor are a thermistor, a platinum hot wire, and an electronic control circuit.

The thermistor measures the temperature of the incoming air. The hot wire is maintained at a constant temperature in relation to the thermistor by the electronic control circuit. An increase in

AIR FLOW SENSORS


air flow will cause the hot wire to lose heat faster and the electronic control circuitry will compensate by sending more current through the wire. The electronic control circuit simultaneously measures the current flow and puts out a voltage signal (VG) in proportion to current flow.

This type of MAF sensor also has an Intake Air Temperature (IAT) sensor as part of the housing assembly. Its operation is described in the IAT section of Temperature Sensors. When looking at the EWD, there is a ground for the MAF sensor and a ground (E2) for the IAT sensor.

AIR FLOW SENSORS


DiagnosisDiagnosis of the MAF sensor involves visual, circuit, and component checks. The MAF sensor passage must be free of debris to operate properly. If the passage is plugged, the engine will usually start, but run poorly or stall and may not set a DTC.

AIR FLOW SENSORS


Vane Air Flow MeterThe Vane Air Flow Meter provides the ECM with an accurate measure of the load placed on the engine. The ECM uses it to calculate basic injection duration and basic ignition advance angle. Vane Air Flow Meters consist of the following components:

• Measuring Plate.

• Compensation Plate.

• Return Spring.

• Potentiometer.

• Bypass Air Passage.

• Idle Adjusting Screw (factory adjusted).

• Fuel Pump Switch.

• Intake Air Temperature (IAT) Sensor.

AIR FLOW SENSORS


During engine operation, intake air flow reacts against the measuring plate (and return spring) and deflects the plate in proportion to the volume of air flow passing the plate. A compensation plate (which is attached to the measuring plate) is located inside a damping chamber and acts as a "shock absorber" to prevent rapid movement or vibration of the measuring plate.

Movement of the measuring plate is transferred through a shaft to a slider (movable arm) on the potentiometer. Movement of the slider against the potentiometer resistor causes a variable voltage signal back to the VS terminal at the ECM. Because of the relationship of the measuring plate and potentiometer, changes in the VS signal will be proportional to the air intake volume.

AIR FLOW SENSORS


The r2 resistor (connected in parallel with r1) allows the meter to continue to provide a VS signal in the event that an open occurs in the main potentiometer (r1). The Vane Air Flow Meter also has a fuel pump switch built into the meter that closes to maintain fuel pump operation once the engine has started and air flow has begun.

The meter also contains a factory adjusted idle adjusting screw that is covered by a tamper -resistant plug. The repair manual does not provide procedures on resetting this screw in cases where it has been tampered with.

Types of VAF MetersThere were two major types of VAF meters. The first design, is the oldest type. It uses battery voltage for supply voltage. With this type of VAF meter, as the measuring plate opens signal voltage increases.

AIR FLOW SENSORS


Karmen Vortex Air Flow MeterThis air flow meter provides the same type of information (intake air volume) as the Vane Air Flow Meter. It consists of the following components:

• Vortex Generator.

• Mirror (metal foil).

• Photo Coupler (LED and photo transistor).

Karman Vortex Air Flow Meter Operation Intake air flow reacting against the vortex generator creates a swirling effect to the air downstream, very similar to the wake created in the water after a boat passes. This wake or flutter is referred to as a "Karman Vortex." The frequencies of the vortices vary in proportion to the intake air velocity (engine load).

AIR FLOW SENSORS


The vortices are metered into a pressure directing hole from which they act upon the metal foil mirror. The air flow against the mirror causes it to oscillate in proportion to the vortex frequency. This causes the illumination from the photo coupler's LED to be alternately applied to and diverted away from a photo transistor. As a result, the photo transistor alternately grounds or opens the 5-volt KS signal to the ECM.

This creates a 5 volt square wave signal that increases frequency in proportion to the increase in intake air flow. Because of the rapid, high frequency nature of this signal, accurate signal inspection at various engine operating ranges requires using a high quality digital multimeter (with frequency capabilities) or oscilloscope.

AIR FLOW SENSORS


ASSIGNMENT NAME: ___________________________

1. Explain the purpose of a Mass Air Flow sensor?

2. List the different types of Mass Air Flow Sensors?

3. Explain in detail the constructions and how a MAF (hot wire type) works?

4. What type of voltage signal is produced by a MAF and what would you expect to change as RPM is increased?

5. Explain in detail the testing procedure of a MAF sensor.

6. Explain in detail the constructions and how a VAF (Vane Air Flow Meter) works?

7. What type of voltage signal is produced by a VAF and what would you expect to change as RPM is increased?

8. Explain in detail the constructions and how a Karmen Vortex works?

9. What type of voltage signal is produced by a Karmen Vortex and what would you expect to change as RPM is increased?

AIR FLOW SENSORS


Pressure Sensors Pressure sensors are used to measure intake manifold pressure, atmospheric pressure, vapor pressure in the fuel tank, etc. Though the location is different, and the pressures being measured vary, the operating principles are similar.

PRESSURE SENSORS


Manifold Absolute Pressure (MAP) SensorIn the Manifold Absolute Pressure (MAP) sensor there is a silicon chip mounted inside a reference chamber. On one side of the chip is a reference pressure. This reference pressure is either a perfect vacuum or a calibrated pressure, depending on the application. On the other side is the pressure to be measured. The silicon chip changes its resistance with the changes in pressure. When the silicon chip flexes with the change in pressure, the electrical resistance of the chip changes. This change in resistance alters the voltage signal. The ECM interprets the voltage signal as pressure and any change in the voltage signal means there was a change in pressure.

Intake manifold pressure is a directly related to engine load. The ECM needs to know intake manifold pressure to calculate how much fuel to inject, when to ignite the cylinder, and other functions. The MAP sensor is located either directly on the intake manifold or it is mounted high in the engine compartment and connected to the intake manifold with vacuum hose. It is critical the vacuum hose not have any kinks for proper operation.

PRESSURE SENSORS


The MAP sensor uses a perfect vacuum as a reference pressure. The difference in pressure between the vacuum pressure and intake manifold pressure changes the voltage signal. The MAP sensor converts the intake manifold pressure into a voltage signal (PIM).

PRESSURE SENSORS


The MAP sensor voltage signal is highest when intake manifold pressure is highest (ignition key ON, engine off or when the throttle is suddenly opened). The MAP sensor voltage signal is lowest when intake manifold pressure is lowest on deceleration with throttle closed.

MAP Sensor DiagnosisThe MAP sensor can cause a variety of driveability problems since it is an important sensor for fuel injection and ignition timing.

Visually check the sensor, connections, and vacuum hose. The vacuum hose should be free of kinks, leaks, obstructions and connected to the proper port.

The VC (VCQ wire needs to supply approximately 5 volts to the MAP sensor. The E2 ground wire should not have any resistance.

Sensor calibration and performance is checked by applying different pressures and comparing to the voltage drop specification. The voltage drop is calculated by subtracting the PIM voltage from the VC voltage.

PRESSURE SENSORS


Barometric Pressure SensorThe Barometric Pressure Sensor, sometimes called a High Altitude Compensator (HAC), measures the atmospheric pressure. Atmospheric pressure varies with weather and altitude. At higher elevations the air is less dense, therefore, it has less pressure. In addition, weather changes air pressure. This sensor operates the same as the MAP sensor except that it measures atmospheric pressure. It is located inside the ECM. If it is defective, the entire ECM must be replaced.

Turbocharging Pressure SensorThe turbocharging pressure sensor operates identically to the MAP sensor and is used to measure intake manifold pressure. The only difference is that when there is boost pressure, the voltage signal goes higher than on a naturally aspirated engine.

PRESSURE SENSORS


Vapor Pressure SensorThe Vapor Pressure Sensor (VPS) measures the vapor pressure in the evaporative emission control system. The Vapor Pressure Sensor may be located on the fuel tank, near the charcoal canister assembly, or in a remote location.

PRESSURE SENSORS


This sensor uses a silicon chip with a calibrated reference pressure on one side of the chip, the other side of the chip is exposed to vapor pressure. Changes in vapor pressure cause the chip to flex and vary the voltage signal to the ECM. The voltage signal out depends on the difference between atmospheric pressure and vapor pressure. As vapor pressure increases the voltage signal increases. This sensor is sensitive to very small pressure changes (1.0 psi = 51.7 mmHg).

Vapor pressure sensors come in variety of configurations. When the VPS is mounted directly on the fuel pump assembly, no hoses are required. For remote locations, there may be one or two hoses connected to the VPS. If the VPS uses one hose, the hose is connected to vapor pressure. In the two hose configuration, one hose is connected to vapor pressure, the other hose to atmospheric pressure. It is important that these hoses are connected to the proper port. If they are reversed, DTCs will set.

PRESSURE SENSORS


VPS DiagnosisCheck all hoses for proper connection, restrictions, and leaks. Check the VC and E2 voltages. Apply the specified pressure and read sensor voltage output. The vapor pressure sensor is calibrated for the pressures found in the EVAP system, so apply only the specified amount to prevent damaging the sensor.

PRESSURE SENSORS


ASSIGNMENT NAME: ___________________________

1. List the different types of Pressure Sensors used on cars?

2. Explain in detail the constructions and how a MAP (Manifold Absolute Pressure) sensor works?

3. What type of voltage signal is produced by a MAP and what would you expect to change as the engine goes from idle to W.O.T.?

4. Explain in detail the testing procedure of a MAP sensor.

5. Explain the need for a Barometric Pressure Sensor?

6. Explain the need for a Turbocharging Pressure Sensor and how does this compare to a MAP sensor?

7. Explain the need for a EVAP Vapor Pressure Sensor and how does this compare to a MAP sensor?

PRESSURE SENSORS


Position / Speed SensorsPosition/speed sensors provide information to the ECM about the position of a component, the speed of a component, and the change in speed of a component. The following sensors provide this data:

• Camshaft Position Sensor (also called G sensor).

• Crankshaft Position Sensor (also called NE sensor).

• Vehicle Speed Sensor.

The Camshaft Position Sensor, Crankshaft Position Sensor, and one type of vehicle speed sensor are of the pick-up coil type sensor.

This type of sensor consists of a permanent magnet, yoke, and coil. This sensor is mounted close to a toothed gear. As each tooth moves by the sensor, an AC voltage pulse is induced in the coil. Each tooth produces a pulse. As the gear rotates faster there more pulses are produced. The ECM determines the speed the component is revolving based on the number of pulses. The number of pulses in one second is the signal frequency.

POSITION / SPEED SENSORS


Pick-Up Coil (Variable Reluctance) Type SensorsThe distance between the rotor and pickup coil is critical. The further apart they are, the weaker the signal.

Not all rotors use teeth. Sometimes the rotor is notched, which will produce the same effect.

These sensors generate AC voltage, and do not need an external power supply. Another common characteristic is that they have two wires to carry the AC voltage.

The wires are twisted and shielded to prevent electrical interference from disrupting the signal. The EWD will indicate if the wires are shielded.

By knowing the position of the camshaft, the ECM can determine when cylinder No. I is on the compression stroke. The ECM uses this information for fuel injection timing, for direct ignition systems and for variable valve timing systems.

This sensor is located near one of the camshafts. With variable timing V-type engines, there is one sensor for each cylinder bank. On distributor ignition systems, it is often called the G sensor and is located in the distributor.

An AC signal is generated that is directly proportional to camshaft speed. That is, as the camshaft revolves faster the frequency increases.



Camshaft Position Sensor (G Sensor)The terminal on the ECM is designated with a letter G, and on some models a G and a number, such as G22 is used.

Variable Valve Position SensorSome variable valve timing systems call the Camshaft Position Sensor the Variable Valve Position Sensor. See section on variable valve timing systems for more information.



Crankshaft Position Sensor (NE Sensor)The ECM uses crankshaft position signal to determine engine RPM, crankshaft position, and engine misfire. This signal is referred to as the NE signal. The NE signal combined with the G signal indicates the cylinder that is on compression and the ECM can determine from its programming the engine firing order. See Section 3 on ignition systems for more information.



Vehicle Speed Sensor (VSS)The ECM uses the Vehicle Speed Sensor (VSS) signal to modify engine functions and initiate diagnostic routines. The VSS signal originates from a sensor measuring transmission/ transaxle output speed or wheel speed. Different types of sensors have been used depending on models and applications.

On some vehicles, the vehicle speed sensor signal is processed in the combination meter and then sent to the ECM.

On some anti-lock brake system (ABS) equipped vehicles, the ABS computer processes the wheel speed sensor signals and sends a speed sensor signal to the combination meter and then to the ECM. You will need to consult the EWD to confirm the type of system you are working on.

Pick-Up Coil (Variable Reluctance) TypeThis type of VSS operates on the variable reluctance principle discussed earlier and it is used to measure transmission/ transaxle output speed or wheel speed depending on type of system.



Magnetic Resistance Element (MRE) Type The MIRE is driven by the output shaft on a transmission or output gear on a transaxle. This sensor uses a magnetic ring that revolves when the output shaft is turning. The MIRE senses the changing magnetic field. This signal is conditioned inside the VSS to a digital wave. This digital wave signal is received by the Combination meter, and then sent to the ECM. The MIRE requires an external power supply to operate.

Reed Switch TypeThe reed switch type is driven by the speedometer cable. The main components are a magnet, reed switch, and the speedometer cable. As the magnet revolves the reed switch contacts open and close four times per revolution. This action produces 4 pulses per revolution. From the number of pulses put out by the VSS, the combination meter/ECM is able to determine vehicle speed.



ASSIGNMENT NAME: ___________________________

1. What are the “G” and “NE” sensors?

2. Explain in detail how an magnetic pick up coil type Cam or Crank sensor works.

3. Explain how the PCM (ECM) uses the Crankshaft position sensor signal.

4. Draw the scope pattern of both a Cam sensor and Crank sensor.

5. What is the function of a vehicle speed sensor (VVS) and list the three types.

6. Explain how a Pick UP Coil (Variable Reluctance) type VSS works?

7. Explain how a Magnetic Resistance Element (MRE) type VSS works?

8. Explain how a Reed Switch type VSS works?



Oxygen and Air/Fuel Ratio SensorsThe ECM uses an oxygen sensor to ensure the air/fuel ratio is correct for the catalytic converter. Based on the oxygen sensor signal, the ECM will adjust the amount of fuel injected into the intake air stream.

There are different types of oxygen sensors, but two of the more common types are:

• the narrow range oxygen sensor, the oldest style, simply called the oxygen sensor.

• wide range oxygen sensor, the newest style, called the air/fuel ratio (A/F) sensor.

Also used on very limited models in the early 90s, was the Titania oxygen sensor.

OBD II vehicles require two oxygen sensors: one before and one after the catalytic converter. The oxygen sensor, or air/fuel ratio sensor, before the catalytic converter is used by the ECM to adjust the air/fuel ratio. This sensor in OBD II terms is referred to as sensor 1. On V-type engines one sensor will be referred to as Bank I Sensor 1 and the other as Bank 2 Sensor 1. The oxygen sensor after the catalytic converter is used by the ECM primarily to determine catalytic converter efficiency. This sensor is refer-red to as sensor 2. With two catalytic converters, one sensor will be Bank 1 Sensor 2 and the other as Bank 2 Sensor 2.

OXYGEN / AIR FUEL SENSORS


Oxygen SensorThis style of oxygen sensor has been in service the longest time. It is made of zirconia (zirconium dioxide), platinum electrodes, and a heater. The oxygen sensor generates a voltage signal based on the amount of oxygen in the exhaust compared to the atmospheric oxygen. The zirconia element has one side exposed to the exhaust stream, the other side open to the atmosphere. Each side has a platinum electrode attached to Zirconium dioxide element.

The platinum electrodes conduct the voltage generated. Contamination or corrosion of the platinum electrodes or zirconia elements will reduce the voltage signal output.



OperationWhen exhaust oxygen content is high, oxygen sensor voltage output is low. When exhaust oxygen content is low, oxygen sensor voltage output is high. The greater the difference in oxygen content between the exhaust stream and atmosphere, the higher the voltage signal.

From the oxygen content, the ECM can determine if the air/fuel ratio is rich or lean and adjusts the fuel mixture accordingly. A rich mixture consumes nearly all the oxygen, so the voltage signal is high, in the range of 0.6 - 1.0 volts. A lean mixture has more available oxygen after combustion than a rich mixture, so the voltage signal is low, 0.4 - 0.1 volts. At the stoichiometric air/fuel ratio (14.7: 1), oxygen sensor voltage output is approximately 0.45 volts.



Small changes in the air/fuel ratio from the stoichiometric point radically changes the voltage signal. This type of oxygen sensor is sometimes referred to as a narrow range sensor because it cannot detect the small changes in the exhaust stream oxygen content produced by changes in the air/fuel mixture. The ECM will continuously add and subtract fuel producing a rich/lean cycle. Refer to Closed Loop Fuel Control in the Fuel Injection section for more information.

NOTE: Think of the oxygen sensor as a switch. Each time the air/fuel ratio is at stoichiometry (14.7: 1) the oxygen sensor switches either high or low.



The oxygen sensor will only generate an accurate signal when it has reached a minimum operating temperature of 400'C (7500F). To quickly warm up the oxygen sensor and to keep it hot at idle and light load conditions, the oxygen sensor has a heater built into it. This heater is controlled by the ECM. See Oxygen Sensor Heater Control for more information.



Air/Fuel Ratio SensorThe Air/Fuel Ratio (A/F) sensor is similar to the narrow range oxygen sensor. Though it appears similar to the oxygen sensor, it is constructed differently and has different operating characteristics.

The A/F sensor is also referred to as a wide range or wide ratio sensor because of its ability to detect air/fuel ratios over a wide range.

The advantage of using the A/F sensor is that the ECM can more accurately meter the fuel reducing emissions. To accomplish this, the A/F sensor:

• operates at approximately 650'C (1200'F), much hotter than the oxygen sensor 400'C (750'F).

• changes its current (amperage) output in relation to the amount of oxygen in the exhaust stream.



OperationA detection circuit in the ECM detects the change and strength of current flow and puts out a voltage signal relatively proportional to exhaust oxygen content.

NOTE: This voltage signal can only be measured by using the Diagnostic Tester or OBD II compatible scan tool. The A/F sensor current output cannot be accurately measured directly. If an OBD 11 scan tool is used, refer to the Repair Manual for conversion, for the output signal is different.

The A/F sensor is designed so that at stoichiometry, there is no current flow and the voltage put out by the detection circuit is 3.3 volts. A rich mixture, which leaves very little oxygen in the exhaust stream, produces a negative current flow. The detection circuit will produce a voltage below 3.3 volts. A lean mixture, which has more oxygen in the exhaust stream, produces a positive current flow. The detection circuit will now produce a voltage signal above 3.3 volts.



NOTEThe A/F sensor voltage output is the opposite of what happens in the narrow range oxygen sensor. Voltage output through the detection circuit increases as the mixture gets leaner.

Also, the voltage signal is proportional to the change in the air/fuel mixture. This allows the ECM to more accurately judge the exact air/fuel ratio under a wide variety of conditions and quickly adjust the amount of fuel to the stoichiometric point. This type of rapid correction is not possible with the narrow range oxygen sensor. With an A/F sensor, the ECM does not follow a rich lean cycle. Refer to Closed Loop Fuel Control in the Fuel Injection chapter for more information.

HINTThink of the A/F sensor as a generator capable of changing polarity. When the fuel mixture is rich (high exhaust oxygen content), the A/F generates current in the negative (-) direction. As the air/fuel mixture gets leaner (less oxygen content), the A/F sensor generates current in the positive (+) direction. At the stoichiometric point, no current is generated.

The detection circuit is always measuring the direction and how much current is being produced. The result is that the ECM knows exactly how rich or lean the mixture is and can adjust the fuel mixture much faster than the oxygen sensor based fuel control system. Therefore, there is no cycling that is normal for a narrow range oxygen sensor system. Instead, A/F sensor output is more even and usually around 3.3 volts.

Oxygen Sensor Diagnosis ServiceThere are several factors that can affect the normal functioning of the oxygen sensor. It is important to isolate if it is the oxygen sensor itself or some other factor causing the oxygen sensor to behave abnormally. See Course 874 Technician Reference book for more information.

A contaminated oxygen sensor, will not produce the proper voltages and will not switch properly. The sensor can be contaminated from engine coolant, excessive oil consumption, additives used in sealants, and the wrong additives in gasoline. When lightly contaminated, the sensor is said to be "lazy," because of the longer time it takes to switch from rich to lean and/or vice versa. This will adversely affect emissions and can produce driveability problems.

Many factors can affect the operation of the oxygen sensor, such as a vacuum leak, an EGR leak, excessive fuel pressure, etc.



It is also very important that the oxygen sensor and heater electrical circuits be in excellent condition. Excessive resistance, opens, and shorts to ground will produce false voltage signals.

In many cases, DTCs or basic checks will help locate the problem.

Oxygen Sensor HeaterFor the oxygen sensor to deliver accurate voltage signals quickly, the sensor needs to be heated. A PTC element inside the oxygen sensor heats up as current passes through it. The ECM turns on the circuit based on engine coolant temperature and engine load (determined from the MAF or MAP sensor signal). This heater circuit uses approximately 2 amperes.

The heater element resistance can be checked with a DVOM. The higher the temperature of the heater, the greater the resistance.

The oxygen sensor heater circuit is monitored by the ECM for proper operation. If a malfunction is detected, the circuit is turned off. When this happens, the oxygen sensor will produce little or no voltage, and possible set DTC P0125.



Air/Fuel Ratio Sensor HeaterThis heater serves the same purpose as the oxygen sensor heater, but there are some very important differences.

Engines using two A/F sensors use a relay, called the A/F Relay, which is turned on simultaneously with the EFI Relay. This heater circuit carries up to 8 amperes (versus 2 amperes for 0, heater) to provide the additional heat needed by the A/F sensor.

This heater circuit is duty ratio controlled pulse width modulator (PMW) circuit. When cold, the duty ratio is high. The circuit is monitored for proper operation. If a malfunction is detected in the circuit, the heater is turned off. When this happens, the A/F sensor will not operate under most conditions and DTC P0125 will set.

Air/Fuel Ratio Sensor Heater DiagnosisDiagnosis of the heater is a similar to the oxygen sensor. Since the A/F sensor requires more heat, the heater is on for longer periods of time and is usually on under normal driving conditions.

Because the heater circuit carries more current, it is critical that all connections fit properly and have no resistance.

The relay is checked in the same manner as other relays.

Titania Element Type Oxygen SensorThis oxygen sensor consists of a semiconductor element made of titanium dioxide (TiO2, which is, like ZrO2, a kind of ceramic). This sensor uses a thick film type titania element formed on the front end of a laminated substrate to detect the oxygen concentration in the exhaust gas.



OperationThe properties of titania are such that its resistance changes in accordance with the oxygen concentration of the exhaust gas. This resistance changes abruptly at the boundary between a lean and a rich theoretical air/fuel ratio, as shown in the graph. The resistance of titania also changes greatly in response to changes in temperature. A heater is, thus built into the laminated substrate to keep the temperature of the element constant.



This sensor is connected to the ECM as shown in the following circuit diagram. A 1.0 volt potential is supplied at all times to the 0" positive (+) terminal by the ECM. The ECM has a built-in comparator that compares the voltage drop at the Ox terminal (due to the change in resistance of the titania) to a reference voltage (0.45 volts). If the result shows that the Ox voltage is greater than 0.45 volts (that is, if the oxygen sensor resistance is low), the ECM judges that the air/fuel ratio is rich. If the 0, voltage is lower than 0.45 volts (oxygen sensor resistance high), it judges that the air/fuel ratio is lean.



ASSIGNMENT NAME: ___________________________

1. What is the purpose and function of an Oxygen Sensor?

2. Explain in detail the operation of the Zirconium Oxygen Sensor

3. Explain in detail how the PCM (ECM) uses the O2 sensor information.

4. Draw an scope pattern of a properly functioning O2 sensor.

5. Explain in detail the test procedure for an zirconium O2 Sensor.

6. Explain in detail the operation of the Air Fuel Ration Sensor.



7. Explain in detail the test procedure for an Air Fuel Ration Sensor.

8. Explain how the heater circuit is controlled in an Air Fuel Ratio Sensor

9. Explain in detail the operation of the Titania Oxygen Sensor.



Knock SensorThe Knock Sensor detects engine knock and sends a voltage signal to the ECM. The ECM uses the Knock Sensor signal to control timing.

Engine knock occurs within a specific frequency range. The Knock Sensor, located in the engine block, cylinder head, or intake manifold is tuned to detect that frequency.

Inside the knock sensor is a piezoelectric element. Piezoelectric elements generate a voltage when pressure or a vibration is applied to them. The piezoelectric element in the knock sensor is tuned to the engine knock frequency.

KNOCK SENSORS


The vibrations from engine knocking vibrate the piezoelectric element generating a voltage. The voltage output from the Knock Sensor is highest at this time.

KNOCK SENSORS


ASSIGNMENT NAME: ___________________________

1. What is the purpose or function of a Knock Sensor?

2. Explain how the PCM (ECM) uses the Knock sensor input signal?

3. Where are Knock sensors usually located?

4. Explain the construction of a Knock Sensor?

5. Draw a scope pattern of a Knock Sensor?

KNOCK SENSORS


Ignition System OverviewThe purpose of the ignition system is to ignite the air/fuel mixture in the combustion chamber at the proper time. In order to maximize engine output efficiency, the air-fuel mixture must be ignited so that maximum combustion pressure occurs at about 10' after top dead center (TDC).

However, the time from ignition of the air-fuel mixture to the development of maximum combustion pressure varies depending on the engine speed and the manifold pressure; ignition must occur earlier when the engine speed is higher and later when it is lower.

IGNITION #1 - IGNITION OVERVIEW


In early systems, the timing is advanced and retarded by a governor advancer in the distributor.

Furthermore, ignition must also be advanced when the manifold pressure is low (i.e. when there is a strong vacuum). However, optimal ignition timing is also affected by a number of other factors besides engine speed and intake air volume, such as the shape of the combustion chamber, the temperature inside the combustion chamber, etc. For these reasons, electronic control provides the ideal ignition timing for the engine.



Electronic Spark Advance OverviewIn the Electronic Spark Advance (ESA) system, the engine is provided with nearly ideal ignition timing characteristics. The ECM determines ignition timing based sensor inputs and on its internal memory, which contains the optimal ignition timing data for each engine running condition. After determining the ignition timing, the ECM sends the ignition Timing signal (IGT) to the igniter. When the IGT signal goes off, the Igniter will turn on shut off primary current flow in the ignition coil producing a high voltage spark (7kV - 35kV) in the cylinder.

Since the ESA always ensures optimal ignition timing, emissions are lowered and both fuel efficiency and engine power output are maintained at optimal levels.

Types of Ignition SystemsIgnition systems are divided into three basic categories:

• Distributor.

• Distributorless Ignition System (DLI) Electronic Ignition.

• Direct Ignition System (DIS).



Essential Ignition System ComponentsRegardless of type the essential components are:

• Crankshaft sensor (Ne signal).

• Camshaft sensor (also called Variable Valve Timing sensor) (G signal).

• Igniter.

• Ignition coil(s), harness, spark plugs.

• ECM and inputs.

Ignition Spark GenerationThe ignition coil must generate enough power to produce the spark needed to ignite the air/fuel mixture. To produce this power, a strong magnetic field is needed. This magnetic field is created by the current flowing in the primary coil. The primary coil has a very low resistance (approximately 1-4 ohms) allowing current flow. The more current, the stronger the magnetic field. The power transistor in the igniter handles the high current needed by the primary coil.

Another requirement to produce high voltages is that the current flow in the primary coil must be turned off quickly. When the transistor in the igniter turns off, current flow momentarily stops and the magnetic field collapses. As the rapidly collapsing magnetic field passes through the secondary winding, voltage (electrical pressure) is created. If sufficient voltage is created to overcome the resistance in the secondary circuit, there will be current flow and a spark generated.



NOTE: The higher the resistance in the secondary circuit, the more voltage that will be needed to get the current to flow and the shorter spark duration. This is important when observing the ignition spark pattern.

IGT SignalThe primary coil current flow is controlled by the ECM through the Ignition Timing (IGT) signal. The IGT signal is a voltage signal that turns on/off the main transistor in the igniter. When IGT signal voltage drops to 0 volts, the transistor in the igniter turns off. When the current in the primary coil is turned off, the rapidly collapsing magnetic field induces a high voltage in the secondary coil. If the voltage is high enough to overcome the resistance in the secondary circuit, there will be a spark at the spark plug.

IGCOn some ignition systems, the circuit that carries the primary coil current is called IGC. lGC is turned on and off by the igniter based on the IGT signal.



IgniterThe primary function of the igniter is to turn on and off the primary coil current based on the IGT signal received from the ECM. The igniter or ECM may perform the following functions:

• Ignition Confirmation (IGF) signal generation unit.

• Dwell angle control.

• Lock prevention circuit.

• Over voltage prevention circuit.

• Current limiting control.

• Tachometer signal.

It is critical that the proper igniter is used when replacing an igniter. The igniters are matched to the type of ignition coil and ECM.

IGF SignalThe IGF signal is used by the ECM to determine if the ignition system is working. Based on IGF, the ECM will keep power supplied to the fuel pump and injectors on most ignition systems. Without IGF, the vehicle will start momentarily, then stall. However, with some Direct Ignition Systems with the igniter in the coil, the engine will run.



IGF Signal Detection using CEMF There are two basic methods of detecting IGF. Early systems used the Counter Electromotive Force (CEMF) created in the primary coil and circuit for generating the IGF signal. The collapsing magnetic field produces a CEMF in the primary coil. When CEMF is detected by the igniter, the igniter sends a signal to the ECM. This method is no longer used.

IGF Detection Using Primary Current MethodThe primary current level method measures the current level in the primary circuit. The minimum and maximum current levels are used to turn the IGF signal on and off. The levels will vary with different ignition systems. Regardless of method, the Repair Manual shows the scope



pattern or provides you with the necessary voltage reading to confirm that the igniter is producing the IGF signal.

Lack of an IGF on many ignition systems will produce a DTC. On some ignition systems, the ECM is able to identify which coil did not produce an IGF signal and this can be accomplished by two methods.

The first method uses an IGF line for each coil.

With the second method, the IGF signal is carried back to the ECM on a common line with the other coil(s). The ECM is able to distinguish which coil is not operating based on when the IGF signal is received. Since the ECM knows when each cylinder needs to be ignited, it knows from which coil to expect the IGF signal.



Dwell Angle ControlThis circuit controls the length of time the power transistor (current flow through the primary circuit) is turned on.

The length of time during which current flows through the primary coil generally decreases as the engine speed rises, so the induced voltage in the secondary coil decreases.

Dwell angle control refers to electronic control of the length of time during which primary current flows through the ignition coil (that is, the dwell angle) in accordance with distributor shaft rotational speed.

Lock Prevention CircuitAt low speeds, the dwell angle is reduced to prevent excessive primary current flow, and increased as the rotational speed increases to prevent the primary current from decreasing.

This circuit forces the power transistor to turn off if it locks up (if current flows continuously for a period longer than specified), to protect the ignition coil and the power transistor.

Over Voltage Prevention CircuitThis circuit shuts off the power transistor(s) if the power supply voltage becomes too high, to protect the ignition coil and the power transistor.



Current Limiting (Over Current Prevention)Current limiting control is a system that improves the rise of the flow of current in the primary coil, ensuring that a constant primary current is flowing at all times, from the low speed to the high speed range, and thus making it possible to obtain a high secondary voltage.

The coil's primary resistance is reduced improving the current rise performance, and this will increase the current flow. But without the current limiting circuit, the coil or the power transistor will burn out. For this reason, after the primary current has reached a fixed value, it is controlled electronically by the igniter so that a larger current will not flow.

Since the current-limiting control limits the maximum primary current, no external resistor is needed for the ignition coil.

NOTE: Since igniters are manufactured to match ignition coil characteristics, the function and construction of each type are different. For this reason, if any igniter and coil other than those specified are combined, the igniter or coil may be damaged. Therefore, always use the correct parts specified for the vehicle.

Tachometer SignalOn some systems the Tach signal is generated in the igniter.



NE Signal and G SignalThough there are different types of ignition systems, the use of the NE and G signals is consistent. The NE signal indicates crankshaft position and engine RPM.

The G signal (also called VVT signal) provides cylinder identification. By comparing the G signal to the NE signal, the ECM is able to identify the cylinder on compression. This is necessary to calculate crankshaft angle (initial ignition timing angle), identify which coil to trigger on Direct Ignition System (independent ignition), and which injector to energize on sequential fuel injection systems.

As ignition systems and engines evolved, there have been modifications to the NE and G signal. Timing rotors have different numbers of teeth. For some G signal sensors, a notch is used instead of a tooth to generate a signal. Regardless, you can determine what style is used by visually examining the timing rotor or consulting the Repair Manual. Many of the different styles are represented with their respective ignition system.



ASSIGNMENT NAME: ___________________________

1. What is Electronic Spark Advance?

2. List the three types of ignition systems:

3. List the five essential ignition system components:

4. Explain the detail the function of the igniter:

5. Explain in detail the function and purpose of both the IGT, IGF, and IGC signals:

6. Define the term Dwell Angle Control”:

7. Explain in detail the function and purpose of both the NE and G signals:



NE Signal and G SignalThough there are different types of ignition systems, the use of the NE and G signals is consistent. The NE signal indicates crankshaft position and engine RPM.

The G signal (also called VVT signal) provides cylinder identification. By comparing the G signal to the NE signal, the ECM is able to identify the cylinder on compression. This is necessary to calculate crankshaft angle (initial ignition timing angle), identify which coil to trigger on Direct Ignition System (independent ignition), and which injector to energize on sequential fuel injection systems.

As ignition systems and engines evolved, there have been modifications to the NE and G signal. Timing rotors have different numbers of teeth. For some G signal sensors, a notch is used instead of a tooth to generate a signal. Regardless, you can determine what style is used by visually examining the timing rotor or consulting the Repair Manual. Many of the different styles are represented with their respective ignition system.

Electronic Spark Advance OperationFor maximum engine output efficiency, the air/fuel mixture must be ignited so that maximum combustion pressure occurs approximately 10’-15' after TDC. As engine RPM increases, there is less time for the mixture to complete its combustion at the proper time because the piston is traveling faster. The ECM controls when the spark occurs through the IGT signal. By varying the time the IGT signal is turned off, the ECM changes ignition spark timing.

IGNITION #2 - ELECTRONIC SPARK ADVANCE


Starting Ignition ControlIgnition timing control consists of two basic elements:

• ignition control during starting.

• after start ignition control.

Ignition Control During StartingIgnition control during starting is defined as the period when the engine is cranking and immediately following cranking. The ignition occurs at a fixed crankshaft angle, approximately 5'- 10' BTDC, regardless of engine operating conditions and this is called the initial timing angle.

Since engine speed is still below a specified RPM and unstable during and immediately after starting, the ignition timing is fixed until engine operation is stabilized.

The ECM recognizes the engine is being cranked when it receives the NE and G signal. On some models, the starter (STA) signal is also used to inform the engine is being cranked.



After-Start Ignition ControlAfter-start ignition control will calculate and adjust ignition timing based on engine operating conditions. The calculation and adjustment of ignition timing is performed in a series of steps, beginning with basic ignition advance control.

Various corrections are added to the initial ignition timing angle and the basic ignition advance angle during normal operation.

After-start ignition control is carried out during normal operation.



The various corrections (that are based on signals from the relevant sensors) are added to the initial ignition timing angle and to the basic ignition advance angle (determined by the intake air volume signal or intake manifold pressure signal) and by the engine speed signal:

Ignition timing = initial ignition timing angle

• basic ignition advance angle

• corrective ignition advance angle

During normal operation of after-start ignition control, the Ignition Timing (IGT) signal calculated by the microprocessor in the ECM and is output through the back-up IC.

Basic Ignition Advance ControlThe ECM selects the basic ignition advance angle from memory based on engine speed, load, throttle valve position, and engine coolant temperature.

Relevant Signals:

• Intake air volume (VS, KS, or VG) (Intake manifold pressure (PIM)).

• Engine speed (NE).

• Throttle position (IDL).

• Engine Coolant Temperature (THW).



Corrective Ignition Advance ControlThe Corrective Ignition Advance Control makes the final adjustment to the actual ignition timing. The following corrective factors are not found on all vehicles.

Warm-Up CorrectionThe ignition timing is advanced to improve driveability when the coolant temperature is low. In some engine models, this correction changes the advance angle in accordance with the intake air volume (intake manifold pressure) and can advance approximately 15' (varies with engine model) by this correction during extremely cold weather.



Over Temperature CorrectionTo prevent knocking and overheating, the ignition timing is retarded when the coolant temperature is extremely high. The timing may be retarded approximately 5' by this correction.

Relevant Signals:

• ECT - THW.

• The following may also be used on some engine models.

• MAF (VS, KS, or VG).

• Engine Speed - NE signal.

• Throttle position TA or (IDL).

Stable Idling CorrectionWhen the engine speed during idling has fluctuated from the target idle speed, the ECM adjusts the ignition timing to stabilize the engine speed. The ECM is constantly calculating the average engine speed. If the engine speed falls below the target speed, the ECM advances the ignition timing by a predetermined angle. If the engine speed rises above the target speed, the ECM retards the ignition timing by a predetermined angle.

This correction is not executed when the engine exceeds a predetermined speed.

In some engine models, the advance angle changes depending on whether the air conditioner is on or off. In other engine models, this correction only operates when the engine speed is below the target engine speed.



Relevant Signals:

• Engine Speed (NE)

• TPS (VTA or IDL)

• Vehicle Speed (SPD)

EGR CorrectionWhen EGR is operating, the ignition timing is advanced according to intake air volume and engine RPM to improve driveability. EGR has the effect of reducing engine knocking, therefore the timing can be advanced.

Relevant Signals:


• TPS (VTA or IDL or PSW

• Intake air volume (VS, KS, or VG) (Intake manifold pressure (PIM))

Torque Control CorrectionThis correction reduces shift shock and the result is that the driver feels smoother shifts. With an electronically-controlled transaxle, each clutch and brake in the planetary gear unit of the transmission or transaxle generates shock to some extent during shifting. in some models, this shock is minimized by delaying the ignition timing when gears are upshifted. When gear shifting starts, the ECM retards the engine ignition timing to reduce the engine torque. As a result, the shock of engagement and strain on the clutches and brakes of the planetary gear unit is reduced and the gear shift change is performed smoothly. The ignition timing angle is retarded a maximum of approximately 200 by this correction. This correction is not performed when the coolant temperature or battery voltage is below a predetermined level.

Relevant Signals:


• TPS (VTA or IDL or PSW

• ECT (THW)

• Battery voltage (+B)



Knock CorrectionEngine knock, if severe enough, can cause engine damage. Combustion chamber design, gasoline octane, air/fuel ratio, and ignition timing all affect when knock will occur. Under most engine conditions, ignition timing needs to be near the point when knock occurs to achieve the best fuel economy, engine power output, and lowest exhaust emissions. However, the point when knock occurs will vary from a variety of factors. For example, if the gasoline octane is too low, and ignition takes place at the optimum point, knock will occur. To prevent this, a knock correction function is used.



When engine knocking occurs, the knock sensor converts the vibration from the knocking into a voltage signal that is detected by the ECM. According to its programming, the ECM retards the timing in fixed steps until the knock disappears. When the knocking stops, the ECM stops retarding the ignition timing and begins to advance the timing in fixed steps. If the ignition timing continues to advance and knocking occurs, ignition timing is again retarded.



The ECM is able to determine which cylinder is knocking by when the knock signal is received. The ECM knows the cylinder that is in the power stroke mode based on the NE and G signals. This allows the ECM to filter any false signals.

Some mechanical problems can duplicate engine knocking. An excessively worn connecting rod bearing or a large cylinder ridge will produce a vibration at the same frequency as engine knocking. The ECM in turn will retard the timing.

Air/Fuel Ratio CorrectionThe engine is especially sensitive to changes in the air - fuel ratio when it is idling, so stable idling is ensured by advancing the ignition timing at this time in order to match the fuel injection volume of air - fuel ratio feedback correction.

This correction is not executed while the vehicle is being driven.

Relevant Signals:

• Oxygen or A/F sensor.

• TPS (VTA or IDL).

• Vehicle Speed (SPD).

Other CorrectionsEngines have been developed with the following corrections added to the ESA system (in addition to the various corrections explained so far), in order to adjust the ignition timing with extremely fine precision.

Transition Correction - During the transition (change) from deceleration to acceleration, the ignition timing is either advanced or retarded temporarily in accordance with the acceleration.

Cruise Control Correction - When driving downhill under cruise control, in order to provide smooth cruise control operation and minimize changes in engine torque caused by fuel cut-off because of engine braking, a signal is sent from the Cruise Control ECU to the ECM to retard the ignition timing.

Traction Control Correction - This retards the ignition timing, thus lowering the torque output by the engine, when the coolant temperature is above a predetermined temperature and the traction control system is operating.



Acoustic Control Induction System (ACIS) Correction - When the engine speed rises above a predetermined level, the ACIS operates. At that time, the ECM advances the ignition timing simultaneously, thus improving output.

Maximum and Minimum Ignition Advance ControlIf the actual ignition timing (basic ignition advance angle + corrective ignition advance or retard angle) becomes abnormal, the engine will be adversely affected. To prevent this, the ECM controls the actual advance so that the sum of the basic ignition and corrective angle cannot be greater or less than preprogrammed minimum or maximum values.

Approximately, these values are:

• MAX. ADVANCE ANGLE: 35'-45'.

• MIN. ADVANCE ANGLE: 100-00.

Advance angle = Basic ignition advance angle + Corrective ignition advance angle



ASSIGNMENT NAME: ___________________________

1. Explain in detail the Electronic Spark Advance Operation:

2. Describe the three Ignition Advance Angles:

3. List the four Relevant Signals of the Basic Ignition Advance Control:

4. Explain “Warm-Up correction:

5. Explain “Over Temperature” correction and list the relevant input signals used:

6. Explain “EGR” correction and list the relevant input signals used:

7. Explain “Stable Idling” correction and list the relevant input signals used:

8. Explain “Knock” correction and list the relevant input signals used:

9. Explain in detail how the PCM (Engine Computer) uses the Knock Sensor to control timing.

10. Explain “Cruise Control” correction:



Distributor Ignition (DI) SystemsThe NE signal is generated by the Crankshaft Position Sensor (also called engine speed sensor). The G signal is generated by the Camshaft Position sensor that may be located in the distributor or on the engine.

IGNITION #3 - DISTRIBUTOR AND DISTRIBUTORLESS TYPES


At the appropriate time during cylinder compression, the ECM sends a signal called IGT to the igniter. This will turn on the transistor in the igniter sending current through the primary winding of the ignition coil. At the optimum time for ignition to occur, the ECM will turn off IGT and the transistor will turn off current flow through the primary winding. The induced current will travel through the coil wire, to the distributor cap, rotor, to the distributor terminal the rotor is pointing at, high tension wire, spark plug, and ground. The rotor position determines the cylinder that receives the spark.



Firing OrderThe firing order can be found in the New Car Features book. The cylinders are identified as follows:

• V-8 engine cylinders are numbered with odd numbered cylinders on the left bank and even numbered cylinders on the right bank.

• V-6 engine cylinders are numbered with even on left bank and odd numbered cylinders on the right bank.

• In-line 6 engines are numbered consecutively 1-6, with the number I cylinder at the front.

• Four cylinder engines are numbered consecutively from front to back.

Many times, original equipment distributor caps have the firing order molded into the cap.



Distributorless & Direct Ignition Systems Overview Essentially, a Distributorless Ignition System is an ignition system without a distributor. Eliminating the distributor improved reliability by reducing the number of mechanical components. Other advantages are:

• Greater control over ignition spark generation - There is more time for the coil to build a sufficient magnetic field necessary to produce a spark that will ignite the air/fuel mixture. This reduces the number of cylinder misfires.

• Electrical interference from the distributor is eliminated - Ignition coils can be placed on or near the spark plugs. This helps eliminate electrical interference and improve reliability.

• Ignition timing can be controlled over a wider range - In a distributor, if too much advance is applied the secondary voltage would be directed to the wrong cylinder.

All of the above reduces the chances of cylinder misfires and consequently, exhaust emissions.

Distributorless Ignition systems are usually defined as having one ignition coil with two spark plug wires for two cylinders. Distributorless Ignition Systems use a method called simultaneous ignition (also called waste spark) where an ignition spark is generated from one ignition coil for two cylinders simultaneously.



Direct Ignition Systems (DIS) have the ignition coil mounted on the spark plug. DIS can come in two forms:

• Independent ignition - one coil per cylinder.

• Simultaneous ignition - one coil for two cylinders. In this system an ignition coil is mounted directly to one spark plug and a high tension cord is connected to the other spark plug. A spark is generated in both cylinders simultaneously.



Distributorless (Simultaneous Ignition) OperationDistributorless Ignition Systems and Direct Ignition Systems that use one coil for two cylinders use a method known as simultaneous ignition. With simultaneous ignition systems, two cylinders are paired according to piston position. This has the effect simplifying ignition timing and reducing the secondary voltage requirement.



For example, on a V-6 engine, on cylinders one and four, the pistons occupy the same cylinder position (both are at TDC and BDC at the same time), and move in unison, but they are on different strokes. When cylinder one is on the compression stroke, cylinder four is on the exhaust stroke, and vice versa on the next revolution.

The high voltage generated in the secondary winding is applied directly to each spark plug. In one of the spark plugs, the spark passes from the center electrode to the side electrode, and at the other spark plug the spark is from the side to the center electrode.



Typically, the spark plugs with this style of ignition system are platinum tipped for stable ignition characteristics.

The voltage necessary for a spark discharge to occur is determined by the spark plug gap and compression pressure. If the spark plug gap between both cylinders is equal, then a voltage proportional to the cylinder pressure is required for discharge. The high voltage generated is divided according to the relative pressure of the cylinders. The cylinder on compression will require and use more of the voltage discharge than the cylinder on exhaust. This is because the cylinder on the exhaust stroke is nearly at atmospheric pressure, so the voltage requirement is much lower.

When compared to a distributor ignition system, the total voltage requirement for distributorless ignition is practically the same. The voltage loss from the spark gap between the distributor rotor and cap terminal, is replaced by the voltage loss in the cylinder on the exhaust stroke in the Distributorless Ignition System.



Direct Ignition System (DIS)As DIS has evolved, there have been changes to the function and location of the igniter. With independent ignition DIS, there may be one igniter for all cylinders or one igniter per cylinder. On simultaneous ignition DIS there is one igniter for all coils. The following gives an overview of the different types used on various engines.

1 MZ-FE 94 DISThis DIS uses one igniter for all coils. The IGF signal goes low when IGT is turned on. The coils in this system use a high voltage diode for rapid cutoff of secondary ignition. If a coil is suspected of being faulty, swap with another coil.



1 MZ-FE with DIS Simultaneous IgnitionThis system uses three IGT signals to trigger the ignition coils in the proper sequence. When a coil is turned on, IGF goes low.



DIS with Independent IgnitionThe DIS with independent ignition has the igniter built into the coil. Typically, there are four wires that make up the primary side of the coil:

• +13.

• IGT signal.

• IGF signal.

• Ground.

The ECM is able to distinguish which coil is not operating based on when the IGF signal is received. Since the ECM knows when each cylinder needs to be ignited, it knows from which coil to expect the IGF signal.

The major advantages of DIS with independent ignition are greater reliability and less chance of cylinder misfire.



Ignition Advance ServiceThough the Diagnostic Tester shows the computed ignition, advance, using a timing light confirms that advance took place and the timing marks are in the correct position.

With Distributor Ignition Systems, the point at which ignition occurs may vary because the base reference point can be moved. It is critical that the base reference point be set to factory specifications.

With DLI and DIS, the base reference point is determined by the Crankshaft Position Sensor and rotor, which is non-adjustable.

The angle to which the ignition timing is set during ignition timing adjustment is called the "standard ignition timing." It consists of the initial ignition timing, plus a fixed ignition advance angle (a value that is stored in the ECM and output during timing adjustment regardless of the corrections, etc., that are used during normal vehicle operation).



Ignition timing adjustment is initiated by connecting terminal T1 (or TE 1) of the check connector or TDCL with terminal E1, with the idle contacts on. This will cause the standard ignition timing signal to be output from the back-up IC in the same way as during after-start ignition control.

The standard ignition timing angle differs depending on the engine model. When tuning up the engine, refer to the repair manual for the relevant engine.

NOTE: Even if terminal T1 or TE1 and terminal E1 are connected, the ignition timing will not be fixed at the standard ignition timing unless the idle contacts are on.

Where the G and NE signal generators are in a fixed position (distributorless or direct ignition systems), ignition timing cannot be adjusted.

DiagnosticsWhen the igniter is built into the ignition coil, it is not possible to do a resistance check of the primary coil winding. A bad primary winding will have to be determined by checking other functions of the coil and the ignition circuit.



DTC 1300 series will set, depending on the engine and type of ignition system, when the ECM does NOT receive the IGF signal. IGF confirms the primary circuit of the ignition system is working. Lack of IGF signal indicates a malfunction in the primary circuit or IGF signal related components.

If the DTC 1300 is set based on IGF, visually check the ignition system and then check for spark. If spark is present, the engine will start then stall when the ECM does not detect IGF (EXCEPT on some engines equipped with DIS with integrated igniter). In addition, when spark is present this confirms the secondary and primary circuits are good. The problem is most likely with the IGF circuitry.



ASSIGNMENT NAME: ___________________________

1. Explain in the difference between Independent (Direct) and Simultaneous (Waste Spark) Ignition systems: (include the number of coils used in each)

2. Explain in detail Simultaneous (Waste Spark) Ignition system operation:

3. Draw a basic 4 cylinder Simultaneous (Waste Spark) Ignition circuit below:

4. Explain in detail Independent (Direct) Ignition system operation:

5. Draw a basic 4 cylinder Independant (Direct) Ignition circuit below:



Fuel Injection SystemThe purpose of the fuel injection system is to precisely inject a metered amount of fuel at the correct time. Based on the input sensor signals, the ECMs programming will decide when to turn each injector on and off.

Fuel Delivery SystemThe purpose of the fuel delivery system is to quietly deliver the proper volume of fuel at the correct pressure. The fuel delivery system must also meet emission and safety regulations. Major components are:

• Fuel Pump.

• Fuel Pump ECU.

• Pressure Regulator.

• Fuel Pressure Control Circuit.

• Fuel Lines.

• Fuel Tank.

• Fuel Filter.

• Pulsation Damper.

• Fuel Injectors.

• Inertia Switch.

FUEL SYSTEMS #1 - OVERVIEW


Return Fuel Delivery SystemWhen the fuel pump is activated by the ECM, pressurized fuel flows out of the tan, through the fuel filter to the fuel rail and up to the pressure regulator. The pressure regulator maintains fuel pressure in the rail at a specified value. Fuel in excess of that consumed by engine operation is returned to the tank by a fuel return line. A pulsation damper, mounted on the fuel rail, is used on many engines to dampen pressure variations in the fuel rail. The injectors, when turned on by the ECM deliver fuel into the intake manifold. When the fuel pump is turned off by the ECM, a check valve in the fuel pump closes maintaining a residual pressure in the fuel system.

Returnless Fuel Delivery System When the fuel pump is activated by the ECM pressurized fuel flows from the pump to the pressure regulator. At the pressure regulator excess fuel is directed to the bottom of the fuel tank and pressurized fuel is sent out of the fuel tank, through the fuel filter, pulsation damper, and into the fuel rail. When the ECM turns on the injectors fuel is delivered into the intake manifold.

Fuel pressure in this system is maintained at a constant and higher pressure, 44-50 psi (301-347 kPa) than the return fuel system. ECM programming and a higher fuel pressure eliminates the need for a vacuum modulated pressure regulator.



The returnless fuel delivery system was adopted because it lowers evaporative emissions since no heated fuel is returned to the fuel tank. On the return fuel delivery system, fuel heated by the engine returns to the fuel tank and has warmer fuel creating more fuel vapors.

Fuel PumpThe fuel pump is mounted in the tank and immersed in fuel. The fuel cools and lubricates the pump. When current flows through the motor, the armature and impeller rotate. The impeller draws fuel in through a filter and discharges pressurized fuel through the outlet port. The fuel pump's pumping capacity is designed to exceed engine requirements. This insures that there will always be enough fuel to meet engine demands.

An outlet check valve, located in the discharge outlet, maintains a residual fuel pressure in the fuel system when the engine is off. This improves starting characteristics and reduces vapor-lock. Without residual fuel pressure, the system would have to be pressurized each time the engine was started and this would increase engine starting (cranking) time. When a hot engine is shut off, fuel temperature in the lines around the engine increases. Keeping the system pressurized increases the boiling point of the fuel and prevents the fuel from vaporizing.

A pressure relief valve will open if the fuel system becomes restricted. This is a safety device to prevent the fuel lines from rupturing and damage to the pump.



On many models the fuel pump is part of the fuel pump assembly. This assembly contains the filters, pressure (fuel system only), sending unit, and fuel pump. Many of the components can be serviced separately.



Jet PumpThe jet pump is an additional pump used when the fuel tank bottom is divided into two chambers. Excess fuel flowing through the fuel return passes through a venturi. This creates a low pressure area around the venturi, and this action will draw the fuel out of Chamber B, and sends it into Chamber A.



Fuel Pump ControlsA variety of fuel pump control circuits and controls have been used over the years. The following basic methods are:

• ON/OFF Control by ECM.

• ON/OFF Control by Fuel Pump Switch.

• ON/OFF Two Speed Control with a Resistor.

• ON/OFF Two Speed Control with Fuel Pump ECU.

• ON/OFF Three Speed Control with Fuel Pump ECU.

The most accurate way of determining the type of fuel control circuit is to look up the circuit in the appropriate EVVD.



The following describes the basic methods of fuel pump control. An essential point to remember is that the fuel pump operates only when the engine is cranking or running.

ON/OFF Control by ECM The following is an explanation of how the fuel pump circuit is activated.

Engine StartWhen the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. At the same time, current flows from the ST terminal of the ignition switch to the L3 coil of the circuit opening relay, turning it on to operate the fuel pump. The fuel pump is now supplying fuel to the fuel injection system.

Note: The circuit opening relay in this example is ground side switched.

Engine RunningOnce the engine starts and the ignition key is moved to the ON (IG) position, current to the L3 coil is shut off, but the ECM will keep the fuel pump on through coil L2 as long as the ECM receives an NE signal. If the NE signal is lost at any time after starting, the ECM turns the fuel pump off.



Engine StoppedWhen the engine stops, the NE signal to the ECM stops. This turns off the transistor, thereby cutting off the flow of current to the L2 coil of the circuit opening relay. As a result, the circuit opening relay opens turning off the fuel pump.

Note: The resistor R and the capacitor C in the circuit-opening relay are for the purpose of preventing the relay contacts from opening when current stops flowing in coil L2 due to electrical noise (fuel pumps controlled by the ECM) or to sudden drops in the intake air volume (fuel pumps controlled by fuel pump switch). They also serve to prevent sparks from being generated at the relay contacts. On some models, an L3 coil is not provided in the circuit-opening relay.

ON/OFF Control by Fuel Pump Switch The fuel pump switch is found on older vehicles using a Vane Air Flow Meter. The air moves the vane when the engine is running closing the fuel pump switch. The following is an explanation of circuit operation.

Engine StartWhen the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. Current also flows from the ST terminal of the ignition switch to the L3 coil of the circuit-opening relay, turning it on to operate the fuel pump. After the engine starts, the cylinders begin drawing in air, causing the measuring plate inside the air flow meter to open. This turns on the fuel pump switch, which is connected to the measuring plate, and current flows to the L2 coil of the circuit-opening relay.



Engine RunningAfter the engine starts and the ignition switch is turned from ST back to IG, current flowing to the L3 coil of the circuit-opening relay is cut off. However, current continues to flow to the L2 coil while the engine is running due to the fuel pump switch inside the air flow meter being on. As a result, the circuit-opening relay stays on, allowing the fuel pump to continue operating.

Engine StoppedWhen the engine stops, the measuring plate completely closes and the fuel pump switch is turned off. This cuts off the flow of current to the L2 coil of the circuit-opening relay. As a result, the circuit-opening relay goes off and the fuel pump stops operating.

Two Speed Fuel Pump ControlLarge displacement engines require a higher volume of fuel during starting and heavy load conditions than small displacement engines. High capacity fuel pumps are used to meet the demand, but they produce more noise and consume more power. To overcome these disadvantages and increase pump life, a two speed fuel pump control is used.

ON/OFF Two Speed Control with a Resistor This type uses a double contact relay and a series limiting resistor.



ON/OFF Two Speed Control with Fuel Pump ECU This type is similar to other systems, but uses a Fuel Pump ECU. In this system, however, ON-OFF control and speed control of the fuel pump is performed entirely by the Fuel Pump ECU based on signals from the ECM. In addition, the Fuel Pump ECU is equipped with a fuel pump system diagnosis function. When trouble is detected, signals are sent from the D1 terminal to the ECM.

High SpeedDuring starting and heavy load condition, the ECM sends a HI signal (about 5 volts) to the FPC terminal of the Fuel Pump ECU. The Fuel Pump ECU then supplies full battery power to the fuel pump.

Low SpeedAfter the engine starts, during idle and light loads, the ECM outputs a low signal (about 2.5 volts) to the Fuel Pump ECU. Then, the Fuel Pump ECU supplies less voltage (about 9 volts) to the fuel pump.

Three Speed Fuel Pump ControlWith this system, the fuel pump is controlled in 3 steps (high speed, medium speed, and low speed).

High SpeedWhen the engine is operating under a heavy load at high RPM or starting, the ECM sends a 5 volt signal to the fuel pump ECU. The fuel pump ECU then applies battery power to the fuel pump causing the fuel pump to operate at high speed.

Medium SpeedUnder heavy loads at low speed, the ECM sends a 2.5 volt signal to the fuel pump control. The fuel pump ECU applies about 10 volts to the fuel pump. This is considered medium speed.



Low SpeedWhen idling or under light loads, the ECM sends a 1.3 volt signal to the fuel pump ECU. The fuel pump ECU applies 8.5 volts to the fuel pump, preventing excessive noise and decreasing power consumption.

Inertia SwitchThe fuel pump inertia switch shuts off the fuel pump when the vehicle is involved in a collision, minimizing fuel leakage.



OperationThe inertia switch consists of a ball, spring loaded link, contact point, and reset switch. If the force of the collision exceeds a predetermined value, the ball will move causing the spring loaded link to drop opening the contact point. This opens the circuit between the ECM and Fuel Pump ECU causing the fuel pump to turn off. If the fuel pump inertia switch has been tripped, it can be reset by pushing up on the reset switch for at least 1 second.



Pressure RegulatorsThe pressure regulator must consistently and accurately maintain the correct fuel pressure. This is important because the ECM does not measure fuel system pressure. It assumes the pressure is correct. There are two basic types of pressure regulators.

Modulated Pressure RegulatorsThe return fuel delivery system uses a pressure regulator located on the fuel pressure rail between the fuel pressure rail and the return line to the fuel tank. There are two types of pressure regulators. One type is modulated by vacuum, the other by atmospheric pressure.

Vacuum Modulated Pressure RegulatorTo maintain precise fuel metering, the vacuum modulated pressure regulator maintains a constant pressure differential across the fuel injector. This means that fuel rail pressure will always be at a constant value above manifold absolute pressure.



Low intake manifold pressure (idle for example) pulls on the diaphragm decreasing spring pressure. This allows more fuel to return to the fuel tank decreasing pressure in the fuel rail. Opening the throttle increases manifold pressure. With less vacuum on the diaphragm spring pressure will increase restricting fuel flow to the fuel tank. This increases pressure in the fuel rail.

Atmospheric Modulated Pressure RegulatorThe atmospheric modulated pressure regulator modifies fuel pressure with changes in atmospheric pressure. A hose is connected from the pressure regulator to the air intake hose between the air filter and throttle plate. Spring pressure and atmospheric pressure keep the fuel pressure at a constant value, 226-265 kPa (38-44 psi). As air pressure changes, such as climbing from low to high altitude, fuel rail pressure decreases because there is less force on the diaphragm.



Constant Pressure Regulator Returnless Fuel Delivery System)The Returnless Fuel Delivery System uses a constant pressure regulator located above the fuel pump in the fuel tank. This type of regulator maintains a constant fuel pressure regardless of intake manifold pressure. Fuel pressure is determined by the spring inside the regulator. Fuel from the fuel pump overcomes spring pressure and some fuel is bypassed into the fuel tank. Fuel pressure is non-adjustable.

High Temperature (Pressure Up) Fuel Pressure ControlSome engines are equipped with a high temperature fuel pressure control to prevent vapor lock for easier starting and better driveability. A three way VSV is connected to the fuel pressure regulator vacuum line. Under normal conditions, the VSV is off and engine vacuum regulates the pressure regulator. If the engine is started when the coolant temperature is 85'C (185'F) or higher and the intake air temperature is above predetermined level, the ECM will turn on the VSV. Engine vacuum is closed off and atmospheric pressure is applied to the pressure regulator diaphragm. This increases fuel pressure preventing vapor lock. Once the engine is started, the VSV may remain on for about 120 seconds.



Fuel Delivery Components Fuel Lines And ConnectorsToday's vehicles use a variety of materials and connectors for fuel lines. Steel and synthetic materials are used, depending on location and model year. It is critical that the correct procedures be followed when servicing the fuel lines.

Connectors can be the threaded type or the quick connector style.



Fuel TankThe fuel tank is designed to safely contain the fuel and evaporative emissions. Typically, it houses the fuel pump assembly and rollover protection valves.

Fuel FiltersTypically, there are two fuel filters in the fuel delivery system. The first filter is the fuel pump filter located on the suction side of the fuel pump. This filter prevents debris from damaging the fuel pump. The second filter, located between the pump and fuel rail, removes dirt and contaminates from the fuel before it is delivered to the injectors. This filter removes extremely small particles from the fuel, the injectors require extremely clean fuel.

The filter may be located in the fuel tank as part of the fuel pump assembly or outside the tank in the fuel line leading to the fuel rail. The filter is designed to be maintenance-free with no required service replacement.



A restricted fuel filter will prevent fuel from reaching the injectors. Therefore, the engine may be hard starting, surge, or have low power under loads. A completely clogged filter will prevent the engine from starting.

Pulsation DamperThe rapid opening and closing of the fuel injectors cause pressure fluctuations in the fuel rail. The result is that the amount of injected fuel will be more or less than the desired amount. Mounted on the fuel rail, the pulsation damper reduces these pressure fluctuations. When pressure suddenly begins to increase the spring loaded diaphragm retracts slightly increasing fuel rail volume. This will momentarily prevent fuel pressure from becoming too high. When pressure suddenly begins to drop, the spring loaded diaphragm extends, slightly decreasing effective fuel rail volume. This will momentarily prevent fuel pressure from becoming too low. Not all engines require the use of a pulsation damper.

The screw mounted at the top of the damper provides an easy check for fuel system pressure. When the screw is up it means the fuel rail is pressurized. Under most conditions, this check is adequate. The screw is nonadjustable and it is used to calibrate the damper at the factory.



Fuel Injection OperationThe fuel injector, when turned on by the ECM, atomizes and directs fuel into the intake manifold.

Fuel InjectorsThere is one injector per cylinder mounted in the intake manifold before the intake valve(s). The injectors are installed with an insulator/seal on the manifold end to insulate the injector from heat and prevent atmospheric pressure from leaking into the manifold. The fuel delivery pipe secures the injector. An O-ring between the delivery pipe and injector prevents the fuel from leaking.



Different engines require different injectors. Injectors are designed to pass a specified amount of fuel when opened. In addition, the number of holes at the tip of the injector varies with engines and model years. When replacing an injector it is critical that the correct injector be used.



Inside the injector is a solenoid and needle valve. The fuel injector circuit is a ground switched circuit, To turn on the injector, the ECM turns on a transistor completing a path to ground. The magnetic field pulls the needle valve up overcoming spring pressure and fuel now flows out of the injector. When the ECM turns off the circuit, spring pressure will force the needle valve onto its seat, shutting off fuel flow.



Injector Timing/Drive CircuitsThe design of the injector drive circuit and ECM programming determines when each injector delivers fuel in relation to the operating cycle of the engine. If the injectors are turned on according to the crankshaft position angle, it is called synchronous injection. That is, the injectors are timed to turn on according to crankshaft position. Depending on engine application, the three main types of synchronous injection designs are: Simultaneous, Grouped, or Sequential. In all these types, voltage is supplied to the injectors from the ignition switch or EFI main relay and the ECM controls injector operation by turning on the driver transistor grounding the injector circuit. Simultaneous and grouped are the oldest styles, and are no longer used.

On simultaneous, all injectors are pulsed at the same time by a common driver circuit. Injection occurs once per engine revolution, just prior to TDC No. 1 cylinder. Twice per engine cycle, one-half of the calculated fuel is delivered by the injectors. With grouped drive circuits, injectors are grouped in combinations. There is a transistor driver for each group of injectors. On sequential drive circuits, each injector is controlled separately and is timed to pulse just before the intake valve opens.

There are times when the ECM needs to inject extra fuel into the engine regardless of crankshaft position and this is called asynchronous injection. Asynchronous injection is when fuel is injected into all cylinders simultaneously when predetermined conditions exist without relation to the crankshaft angle. Two common conditions are starting and acceleration.

FUEL SYSTEMS #2 - INJECTION DURATION CONTROLS


Note: The EWD injector circuit can identify if the injection system is a grouped or sequential. A sequential system will have one injector per injector driver.

Fuel Injection Volume ControlThe amount of fuel injected depends on fuel system pressure and the length of time the injector is turned on. Fuel system pressure is controlled by the pressure regulator, and injector on time is controlled by the ECM. The time the injector is on is often called duration or pulse width, and it is measured in milliseconds (ms). Cold starting requires the highest pulsewidth. Pulsewidth is dependent primarily on engine load and engine coolant temperature. The higher the engine load and the more the throttle is opened to let air in, the greater pulsewidth increases. The ECM determines the duration based on the input sensor signals, engine conditions, and its programming.



Start ModeWhen the ignition switch is in the Start position, the ECM receives a voltage signal at the STA terminal. The ECM determines basic injection duration based on the ECT (THW) signal. On MAP sensor equipped engines the ECM will then modify this duration based on the IAT (THA) signal.



The ECM will adjust the duration based on battery voltage. During cranking, battery voltage is much lower causing the injector valve to lift slowly. The ECM corrects for this by increasing injection duration.

When the ECM receives the NE signal (Crankshaft Position Sensor), all the injectors are turned on simultaneously. This insures there is enough fuel for starting the engine. Note that below freezing, injection duration increases drastically to overcome the poor vaporization characteristics of fuel at these temperatures.

Engine Running (After Start) Injection Duration Control

Total fuel injection duration is determined in three basic steps:

• Basic injection duration.

• Injection corrections.

• Voltage correction.

Basic injection duration is based on air volume and engine RPM. Air volume on MAF equipped engines is determined by the MAF voltage signal.



On MAP sensor equipped engines, the ECM calculates air volume based on the PIM signal, engine RPM, THA signal, and volumetric efficiency values stored in the ECM.

Injection corrections adjust the basic injection duration to accommodate different engine modes and operating conditions. It is based on a variety of input signals.

Voltage correction adjusts the injection duration to compensate for differences in the electrical system voltage.

After Start EnrichmentImmediately after starting (engine speed above a predetermined level), the ECM supplies an extra amount of fuel for a certain period of time to stabilize engine operation.

This correction volume is highest immediately after the engine has started and gradually decreases. The maximum correction volume value is based on engine coolant temperature. The hotter the engine, the less volume of fuel injected.

Warm-Up EnrichmentA rich fuel mixture is needed to maintain driveability when the engine is cold. The ECM injects extra fuel based on engine coolant temperature. As the engine coolant warms up, the amount of warm-up enrichment decreases. Depending on the engine, warm-up enrichment will end at approximately 50'C-80'C (122'F-176’F).

If the ECM is in Fail-Safe Mode for DTC PO 115, the ECM substitutes a temperature value, usually 80'C (176'F).



Correction Based on Intake Air Temperature (MAP Sensor Equipped Engines)The density of the intake air decreases as temperature increases. Based on the IAT (THA) signal, the ECM adjusts the fuel injection duration to compensate for the change in air density. The ECM is programmed so that at 20'C (68'R no correction is needed. Below 20'C (68'F), duration is increased, above 20'C (68'F), duration is decreased.

If the ECM is in Fail-Safe Mode for DTC P0110, the ECM substitutes a temperature value of 20'C (68’F).

Power Enrichment CorrectionWhen the ECM determines the engine is operating under moderate to heavy loads, the ECM will increase the fuel injection duration. The amount of additional fuel is based on the MAF or MAP sensors, TPS, and engine RPM. As engine load (and air volume) increases, fuel injection duration increases. As engine RPM increases, injection frequency increases at the same rate.

Acceleration CorrectionOn initial acceleration, the ECM extends the injection duration richening the mixture to prevent a stumble or hesitation. The duration will depend on how far the throttle valve travels and engine load. The greater the throttle travel and engine load, the longer the injection duration.



Deceleration Fuel CutDuring closed throttle deceleration periods from moderate to high engine speeds, fuel delivery is not necessary or desirable. To prevent excessive decel emissions and improve fuel economy, the ECM will not open the injectors under certain decel conditions. The ECM will resume fuel injection at a calculated RPM.

Referring to the graph, fuel cut-off and resumption speeds are variable, depending on coolant temperature, A/C clutch status, and the STA signal. Essentially, when extra engine loads are present, the ECM will begin fuel injection earlier.

Fuel Tau Cut is a mode employed on some engines during long deceleration time with the throttle valve closed. During these times, excess oxygen would enter the catalytic converter. To prevent this, the ECM will very briefly pulse the injectors.

Engine Over-Rev Fuel CutoffTo prevent engine damage, a rev-limiter is programmed into the ECM. Any time the engine RPM exceeds the pre-programmed threshold, the ECM shuts off the injectors. Once RPM falls below the threshold, the injectors are turned back on. Typically, the threshold RPM is slightly above the engine's redline RPM.

Vehicle Over-Speed Fuel CutoffOn some vehicles, fuel injection is halted if the vehicle speed exceeds a predetermined threshold programmed into the ECM. Fuel injection resumes after the speed drops below this threshold.



Battery Voltage CorrectionThe applied voltage to the fuel injector will affect when the injector opens and the rate of opening. The ECM monitors vehicle system voltage and will change the injection on time signal to compensate. If system voltage is low, the injection on time signal will be longer, but the actual time the injector is open will remain the same (if system voltage were higher).



EVAP Purge CompensationWhen the evaporative purge valve is on, fumes from the charcoal canister are drawn into the intake manifold. The ECM will compensate based on the oxygen sensor output and shorten the injector pulse width.



ASSIGNMENT NAME: ___________________________

1. Explain in detail both Grouped Injection and Sequential Injection?

2. What inputs are use for Injection Duration control during “After start”?

3. Explain detail “Afterstart Enrichment Correction”

4. Explain in detail “Warm-Up Enrichment Correction”

5. Explain explain the “Fuel Correction” based on Intake Air Temperature (MAP sensor equipped engines:

6. Explain in detail “Power Enrichment Correction”



7. Explain in detail “Acceleration Enrichment Correction”

8. Explain in detail “Deceleration Fuel Cut”

9. Explain in detail the “Engine Over-Rev Fuel Cutoff”

10. Explain in detail “Vehicle Over-Speed Fuel Cutoff”

11. Explain in detail “Battery Voltage Correction”

12. Explain in detail “EVAP Canister Purge Compensation”



Closed Loop SystemsA system that controls its output by monitoring its output is said to be a closed loop system. An example of a closed loop system is the vehicle's charging system. The voltage regulator adjusts the voltage output of the alternator by monitoring alternator voltage output. If voltage is too low, the voltage regulator will increase alternator output. Without the voltage regulator, alternator output could not be adjusted to match the electrical loads. Many systems are closed loop systems. Some other examples are: cruise control, ignition system knock control, idle speed control, and closed loop air/fuel ratio correction control. When the ECM corrects the air/fuel ratio based on the oxygen or air/fuel ratio sensor, the system is said to be in closed loop.

Open Loop SystemsAn open loop system does not monitor its output and make adjustments based on its output. The temperature control in a vehicle not equipped with automatic air conditioning serves as an example.

Closed Loop Fuel ControlThe ECM needs to monitor the exhaust stream and adjust the air/fuel ratio so that the catalytic converter will operate at peak efficiency, reducing regulated emission gases. Measuring the amount of oxygen remaining after combustion is a means to indicate the air/fuel ratio. A richer mixture will consume more oxygen during combustion than a leaner mixture. The oxygen sensor or air/fuel ratio sensor measures the amount of oxygen remaining after combustion in the exhaust stream. From this information, the ECM will control the injection duration to achieve the desired, ideal air/fuel ratio of 14.7: 1. This is necessary so the catalytic converter will operate at peak efficiency.

Note: The engine operation often requires different air/fuel ratios for starting, maximum power, and maximum fuel economy. The 14.7:1 ratio is for catalytic converter efficiency.

FUEL SYSTEMS #3 - CLOSED LOOP / FUEL TRIM


Stoichiometry and Catalyst EfficiencyFor the catalytic converter to operate at peak efficiency, the air/fuel ratio must be at the ideal stoichiometric ratio of 14.7 parts air to one part fuel as measured by weight. This why the ECM tries to maintain a 14.7 to I ratio whenever possible.



Open Loop ModeThe ECM will be in open loop mode when:

• starting the engine.

• the engine is cold.

• hard acceleration.

• during fuel cut-off.

• wide open throttle.

If the engine will not go into closed loop mode, the problem may be insufficient engine temperature, no response from the oxygen sensor or air/fuel sensor, or the heater circuit is inoperative. Usually, no response from the oxygen or A/F sensor will set DTC P0125.

If there is a driveability problem only in closed loop, anything that disrupts air/fuel ratio, the oxygen or A/F sensor circuit may be the cause.



Closed Loop Operation/Oxygen SensorWhen in closed loop, the ECM uses the oxygen sensor voltage signal to make minor corrections to the injection duration. This is done to help the catalytic converter operate at peak efficiency.

When the voltage is higher than 450 mV, the air/fuel ratio is judged to be richer than the ideal air/fuel ratio and the amount of fuel injected is reduced at a constant rate. The reduction in the duration continues until the oxygen sensor signal switches to a low voltage (lean air/fuel ratio).



When the voltage signal is lower than 450 mV, the air/fuel ratio is judged to leaner than the ideal air/fuel ratio so the amount of fuel injected is increased at a constant rate. The increase in duration continues until the oxygen sensor switches to high voltage (rich air/fuel ratio). At this point, the ECM will slowly decrease the amount of fuel, therefore the air/fuel ratio oscillates slightly richer or leaner from the ideal air/fuel ratio. The result is an average of approximately 14.7: 1. This produces the proper mixture of exhaust gases so that the catalytic converter operates at its most efficient level.

The frequency of this rich/lean cycle depends on exhaust flow volume (engine RPM and load), the oxygen sensor response time, and the fuel control programming. At idle, exhaust flow volume is low, and the switching frequency of the oxygen sensor is low. As engine speed increases, the switching frequency of the oxygen sensor increases, generally eight or more times at 2,500 RPM in ten seconds.

Closed Loop Operation Air/Fuel SensorWith an A/F sensor, air/fuel mixture correction is faster and more precise. An oxygen sensor signal voltage abruptly changes at the ideal A/F ratio and changes very little as the air/fuel ratio extends beyond the ideal ratio. This makes fuel control less precise, for the ECM must gradually and in steps change the injection duration until the oxygen sensor signal abruptly switches.

By contrast, the A/F sensor outputs a voltage signal that is relatively proportional to the A/F ratio. The ECM now knows how much the A/F ratio has deviated from the ideal, and thus, the fuel control program can immediately adjust the fuel injection duration. This rapid correction reduces emission levels because the ECM can more accurately maintain the ideal air/fuel ratio for the best catalytic converter efficiency.

Therefore, when observing A/F sensor voltage output, the output is relatively constant because there is no cycling between rich and lean.

Fuel TrimAs the engine and sensors change over time, the ECM needs a method to adjust the injection duration for improved driveability and emission performance. Fuel trim is a program in the ECM designed to compensate for these changes.

When in closed loop, the ECM modifies the final injection duration based on the oxygen sensor. These minor corrections are needed to maintain the correct air/fuel ratio. However, if more correction than normal (as determined by the ECM) is needed, the ECM will use the fuel trim strategy to compensate. Fuel trim allows the ECM to learn and adjust the injection



duration quickly by reducing the correction time back to normal. This means that driveability and performance will not suffer.

Fuel trim can be observed on the Diagnostic Tester as a percentage. A positive percentage means that the ECM has increased the duration and a negative percentage means the ECM has decreased the duration.

There are two different fuel trim values that affect final injection duration and can be observed by the technician; short term fuel trim (SHORT FT) and long term fuel trim (LONG FT). SHORT FT is a temporary addition or subtraction to the basic injection duration. LONG FT is part of the basic injection duration calculation and it is stored in the ECM's memory.

SHORT FTSHORT FT is based on the oxygen sensor, and therefore, it only functions in closed loop. SHORT FT responds rapidly to changes in the oxygen sensor. If SHORT FT is varying close to 0%, little or no correction is needed. When SHORT FT percentage is positive, the ECM has added fuel by increasing the duration. A negative percentage means the ECM has subtracted fuel by decreasing the duration. The SHORT FT value is temporary and not stored when the ignition key is turned off.

SHORT FT is used to modify the long term fuel trim. When the SHORT FT remains higher or lower longer than expected, the ECM will add or subtract this value to the LONG FT.

LONG FTLONG FT is stored in memory because it is part of the basic injection duration calculation. The ECM uses the SHORT FT to modify the LONG FT. The LONG FT does not react rapidly to sudden changes, it only changes when the ECM decides to use the SHORT FT value to modify the LONG FT. LONG FT is stored in the ECM's memory and it is not erased when the ignition key is turned off. Because LONG FT is part of the basic injection duration, it affects injection duration in closed and open loop. Like the SHORT FT, when LONG FT is at 0% there has been no modification to the basic injection duration. A positive percentage means the ECM is adding fuel; a negative percentage, subtracting fuel.

Fuel System MonitorThe fuel system monitor is designed to set a DTC if the fuel injection system is going to exceed emission standards. This monitor uses the fuel trim correction levels for detection. The amount of fuel trim correction that will set a DTC varies with each engine type and model year.



ASSIGNMENT NAME: ___________________________

1. Explain in detail Open Loop Operation?

2. Explain in detail Closed Loop Operation?

3. Explain the relationship between “Stiochometric Fuel Ratio” and “Catalytic Converter efficiency”:

4. List the five engine conditions when the ECM will be in “Open Loop Mode”:

5. Explain in detail how the ECM uses the Oxygen Sensor to control fuel duration:

6. Explain the term “Fuel Trim”

7. Explain in detail both “SHORT Fuel Trim” and “LONG Fuel Trim”;



OBD (On-Board Diagnostic System, Generation 1)In April 1985, the California Air Resources Board (CARB) approved On-Board Diagnostic system regulations, referred to as OBD. These regulations, which apply to almost all 1988 and newer cars and light trucks marketed in the State of California, require that the engine control module (ECM) monitor critical emission related components for proper operation and illuminate a malfunction indicator lamp (MIL) on the instrument panel when a malfunction is detected. The OBD system also provides for a system of Diagnostic Trouble Codes (DTC) and fault isolation logic charts in the repair manual, to assist technicians in determining the likely cause of engine control and emissions system malfunctions. The basic objectives of this regulation are twofold:

• To improve in-use emissions compliance by alerting the vehicle operator when a malfunction exists.

• To aid automobile repair technicians in identifying and repairing malfunctioning circuits in the emissions control system.

OBD self diagnosis applies to systems which are considered to be most likelyto cause a significant increase in exhaust emissions if a malfunction occurs.Most notably, this includes:

• All major engine sensors• The fuel metering system• Exhaust gas recirculation (EGR) function

OVERVIEW OF OBD AND REGULATIONS


Malfunction Indicator Light (MIL)When a malfunction occurs, the MIL remains illuminated as long as the fault is detected and goes off once normal conditions return, leaving a Diagnostic Trouble Code (DTC) stored in the ECM memory. Circuits are monitored for continuity, shorts, and in some cases, normal parameter range.

The Malfunction Indicator Light (MIL) is also a visual inspection item in most emissions inspection and maintenance programs U/M), allowing the emissions inspector to make a quick visual determination whether the engine control/emissions system is functioning normally. During the visual inspection phase of the I/M test, the inspector must observe the MIL during a "key on bulb check" and again with the engine running. The MIL should be on during the bulb check and go off when the engine starts. When a vehicle passes this check, it is highly probable that the engine control system is functioning normally.

Although the OBD regulation applies only to California emissions certified vehicles, some or all of the OBD system features are found on Federal emissions certified vehicles as well.

OBD Diagnostic Trouble Codes (DTC)Diagnostic Trouble Codes or DTCs are generated by the on-board diagnostic system and stored in the ECM memory. They indicate the circuit in which a fault has been detected. DTC information remains stored in the ECM long term memory regardless of whether a continuous (hard) fault or intermittent fault caused the code to set. Toyota products with OBD will continue to store a DTC in the ECM long term memory until the code is cleared by removing power from the ECM BATT terminal. In most cases, the EFI fuse powers this keep alive memory.



Serial Data StreamsAlthough not required by the OBD regulation, the use of serial data accessible by special scan tools, has been introduced by some manufacturers. Serial data is electronic information about sensors, actuators, and ECM fuel/spark strategy, which is accessed from a single wire coming from the ECM. The term serial data implies that the information is digitally coded and transmitted in a series of data words. The data words are decoded and displayed by a scan tool.

The typical Toyota OBD serial data stream consists of up to 20 data words including sensor values, switch status, actuator status, and other engine operating data.

OBD-II (On-Board Diagnostic System, Generation 2)Although OBD supplies valuable information about a number of critical emissions related systems and components, there are several important items which were not incorporated into the OBD standard due to technical limitations at the time that the system was phased into production (during the 1988 model year.) Since the introduction of OBD, several technical breakthroughs have occurred. For example, the technology to monitor engine misfire and catalyst efficiency has been developed and implemented on production vehicles.



OBD-II (On-Board Diagnostic System, Generation 2) Continued As a result of these technical breakthroughs and because existing I/M programs have proven to be less effective than desired in detecting critical emissions control system defects which occur during normal road load operation, a more comprehensive OBD system was developed under the direction of CARB.

OBD-II, which is implemented over the 1994 through 1996 model years, adds catalyst efficiency monitoring, engine misfire detection, canister purge system monitoring, secondary air system monitoring, and EGR system flow rate monitoring. Additionally, a serial data stream consisting of twenty basic data parameters and diagnostic trouble codes is a required part of the diagnostic system.

In addition to the basic required OBD-II data stream, Toyota has an enhanced data stream which consists of approximately 60 additional data words. Access to all OBD-II data is made by connecting a generic scan tool to a standardized Data Link Connector (DLC) located under the left side of the instrument panel. The standards for data, the scan tool, diagnostic test modes, diagnostic trouble codes, and everything related to the introduction of the OBD-II regulation are established by the Society of Automotive Engineers.

The goal of the OBD-II regulation is to provide the vehicle with an on-board diagnostic system which is capable of continuously monitoring the efficiency of the emissions control system, and to improve diagnosis and repair efficiency when system failures occur. In essence, an emissions I/M station will be programmed into every OBD-II equipped vehicle.

OBD-II FeaturesThe following information will familiarize you with the highlights of the OBD-II system features:

Oxygen Sensor (02S) DiagnosticsEnhanced diagnostics for the oxygen sensor(s) include monitoring for degradation and contamination by monitoring switching frequency and lean-rich, rich-lean switch time.

Fuel System MonitoringMost fuel systems continually shift their base calibration to compensate for changes in atmospheric pressure, temperature, fuel composition, component variations, and other factors. This adaptive behavior is normal as long as it remains within the design limits of the system.

When conditions occur which cause the fuel system to operate outside of its design parameters, for example, a skewed air flow meter signal, incorrect fuel pressure, or other mechanical problems, the OBD-II system is designed to detect this abnormal operating condition. If the condition occurs for longer than a specified amount of time, a DTC will be stored. When a DTC stores, the engine speed, load, and warm-up status is stored in a retrievable serial data freeze frame.



Misfire MonitoringBy using a high frequency crankshaft position signal, the ECM can closely monitor crankshaft speed variations during individual cylinder power strokes. When an engine is firing cleanly on all cylinders, the crankshaft speeds up with each power stroke. When misfire occurs, crankshaft speed increase is effected for that cylinder.

Toyota OBD-II engines use a 36 minus 2 tooth Ne sensor which directly measures crankshaft speed and position. This information is processed by the ECM to determine if misfire occurs, which cylinder it is occurring in, and the degree of misfire.

When a misfire of any significance is detected, a DTC is stored and the engine speed, load and warm-up status at the time of misfire will be stored. Additionally, the vehicle operator will be alerted to the condition by a rapidly flashing MIL during periods when significant misfire is occurring.



Catalyst MonitoringA sub-oxygen sensor (S2) placed downstream, at the outlet of the catalytic converter, is monitored for switching frequency and compared to the switching frequency of the main oxygen sensor (S1), placed upstream of the catalyst. The oxidation efficiency of the catalyst can be determined by comparing the switching frequency of these two sensors. As the catalyst conversion efficiency declines, the switching frequency of sensor 2 increases, approaching that of sensor 1. In addition to being used for diagnostics, sensor 2 also assists in maintaining optimum fuel control when the catalyst begins to degrade.

EGR System MonitoringEnhanced monitoring of EGR flow rate characteristics include the ability to detect flow rates which are above or below the design flow rate for a given engine operating condition. One method of accomplishing this is to simply monitor the change in temperature on the intake side of the EGR passage. Another method is to measure the degree of rich correction to the fuel delivery system as EGR flow is momentarily inhibited.



Evaporative Purge System Monitoring By monitoring the oxygen sensor and injection pulse width as the canister is being purged, the ECM can detect the reduction of exhaust oxygen content and corresponding decrease in injection pulse width to correct for this momentary rich condition. In this manner, the ECM can detect a failure in the canister purge control system and store a DTC to alert the vehicle operator of the malfunction. Purge flow monitoring is only used on 95 and later OBD-Il equipped vehicles.

Secondary Air System MonitoringBy switching secondary air upstream of the oxygen sensor momentarily during closed loop operation, the ECM can monitor the oxygen sensor response and corresponding injection pulse width increase to determine if the secondary air system is functioning normally.

Malfunction Indicator Light IlluminationOnce a malfunction has been established (two trip detection logic where applicable) the MIL will illuminate and remain illuminated even if the condition is intermittent. The MIL will remain on after subsequent restarts even if the malfunction condition is no longer present. The OBD-II system can only extinguish the MIL if the malfunction does not reoccur during three subsequent sequential trip cycles.

The OBD-II system can only erase a stored DTC if the malfunction is not detected during forty sequential trip cycles. Toyota systems do not erase the code, but rather place a flag on any code which does not reoccur during 40 subsequent trip cycles.

DTCs can be erased using the generic scan tool or by removing power from the ECM BATT terminal.

Readiness TestThe OBD-II diagnostic system continually monitors for misfire and fuel system faults. It also performs a functional test on the catalyst, EGR system, and oxygen sensors once during every driving cycle or "trip ". Certain driving conditions must be encountered before these systems can be confirmed as operating normally. For example, the engine must be fully warmed up, throttle angle must have exceeded a specified angle, the engine must have achieved a specified load, and so on.

In the event that these driving conditions have not been met, the ECM will not have completed its "readiness test", and is not capable of displaying supported test data. Under these conditions, the scan tool will display a message indicating that "not all supported readiness tests are complete", warning the operator that this test data is not available.



Readiness Test ContinuedThe readiness test is a flag which is used during I/M inspections to indicate that the vehicle on-board diagnostic system cannot supply information required during the test. In this case, the vehicle must be operated until all readiness testing conditions have been satisfied.



Stored Engine Freeze Frame DataUpon detection of a malfunction, the OBD-II system will store all data at the time that the DTC set. This freeze frame data can be retrieved using the generic scan tool.

Standardization of Service Information and DTCsUnder the provisions of OBD-II regulations, emissions related diagnostic and service information will be readily available to the service industry, from the vehicle manufacturer. This information includes procedures and specifications necessary to diagnose the engine control system. Although enhanced diagnostics may be available using special equipment and procedures, at a minimum, repair procedures will be written using the generic scan tool and other commonly available test equipment like multimeters; and oscilloscopes.

In an effort to simplify diagnostics, OBD-II requires that all manufacturers standardize DTCs on OBD-II equipped vehicles. Eventually, all emissions related service information will be standardized in format and available through an electronic media.



Clean Air Act Amendments of 1990On November 15, 1990, the Clean Air Act was amended, directing the Environmental Protection Agency (EPA) to promote new regulations, under section 207(a), requiring automobile manufacturers to install on-board diagnostic systems capable of.

• Identifying deterioration or malfunction of major emissions components which could result in vehicle failure to comply with federal emissions standards.

• Alerting the vehicle operator of the need to maintain and/or repair emissions related components and/or systems.

• Storing DTCs and providing access to vehicle on-board information.

Additionally, manufacturers will:• Make available to all interested parties, all necessary emissions maintenance and repair

information.

Adoption of these provisions was prompted by the fact that in 1990, 96urban areas in the U.S. were in violation of National Ambient Air QualityStandards (NAAQS) for ozone and 41 areas for carbon monoxide.

Although CAAA'90 regulations vary slightly from CARB OBD-II, EPA has elected to adopt California OBD-II for Federal emissions certification, effective with the '96 model year. Beginning in the '98 model year, a new Federal OBD standard will be adopted, effectively eliminating the different status between California and Federal emissions certification.



What is Serial Data? Serial data is electronically coded information which is transmitted by one computer and received and displayed by another computer. Using an analog/digital circuit, the transmitting computer digitizes the data from sensors, actuators, and other calculated information. Typically, this means that each sensor or actuator value is converted into a one byte (8 bits) binary word before it is transmitted to the receiving computer.

In order to display the data in familiar units that you are used to working with, the receiving computer interprets each binary word as it is received and displays it as an analog voltage, temperature, speed, time, or other familiar unit of measurement.

Serial data gets its name from the fact that data parameters are transmitted, one after another, in series. The display on the receiving computer updates or refreshes once each data cycle, after all data has been received. Therefore the refresh rate of the data is determined by how many words are on the data stream and how quickly the data is transmitted.

The data transmission rate is referred to as the baud rate. Baud rate refers to the number of data bits that can be transmitted per second. For example, if a data stream has 12 parameters, and each parameter is converted into an 8 bit data word, the total size of the data transmission is 96 bits of data (12 words x 8 bits per word.) If this data can be transmitted once every second, the baud rate is 96 bits/second or 96 baud. In this case, the display screen will refresh data values once every second.

SERIAL DATA


In the case of Toyota engine control systems, there are three different types of serial data which can be received and displayed by your Diagnostic Tester, depending on application. These are OBD, OBD-II, and V-BoB. In all three cases, data is digitized by the transmitting computer (ECM or V-BoB) and displayed by the Diagnostic Tester. The main difference between these three data sources are the specific parameters available on the data stream and the speed at which data can be transmitted and refreshed on the Diagnostic Tester display.

SERIAL DATA


Displaying Engine DataThe type of serial data available depends on the vehicle you are working on. Many Toyota vehicles with OBD, manufactured since 1989, have a serial data stream available on the VF1 terminal of DLC 1 (Check connector) or the ENG terminal of DLC 2 (TDCL).

Vehicles which support a serial data stream can be identified by the presence of a TE2 circuit (see the application matrix on page 86 of this handbook). Depending on the vehicle, there can be as many as 20 different sensor, actuator, and diagnostic data parameters represented on the OBD data stream.

The OBD-II system, which phased in during the 1994 through 1996 model years, has a high speed data stream available on terminal 2 of DLC 3 01962 connector). There are in excess of 50 data parameters represented on the OBD-II engine data stream.

Accessing serial data on any of these vehicles is a simple matter using the Diagnostic Tester.

SERIAL DATA


For 1989 and later models which do not support serial data streams, the Vehicle Break-out Box gives you the ability to create one. By connecting the V-BoB in series with the ECM, information from every wire can be serialized and displayed by the Diagnostic Tester. Although it takes a little bit longer to install the V-BoB, the unlimited amount of high speed data makes the effort well worth the time invested.

SERIAL DATA


The OBD Diagnostic CircuitThis unidirectional data stream typically consists of 14 to 20 data words representing primarily sensor inputs and three outputs; injection pulse width, spark advance angle, and idle speed control command. Data is transmitted at a rate of 100 baud, updating on the Diagnostic Tester display approximately once every 1.25 seconds. Depending on application, the data is accessed from either DLC 1 or DLC 2. Data is triggered by grounding the TE2 circuit and reading the VF1 circuit.

Diagnostic Trouble Codes can be displayed using the Diagnostic Tester or by grounding the TE1 circuit and counting the Malfunction Indicator Lamp (MIL) flashes. The scan tool reads codes by counting the low voltage pulses on the W terminal of the Diagnostic Link Connector (DLC). Therefore, code retrieval is a relatively slow process, especially when multiple codes are stored.

SERIAL DATA


The OBD-II Diagnostic CircuitThe OBD-II data line is a bi-directional communication link which is capable of transmitting and receiving data. This feature allows the Diagnostic Tester to operate system actuators and send commands to the ECM in addition to displaying system data.

The high speed OBD-II data stream typically consists of 50 to 75 data words representing virtually all sensor inputs, actuator outputs, several calculated parameters, many fuel feedback related parameters, and cylinder misfire data. The data is transmitted at a rate of 10.4 Kilo baud, giving the Diagnostic Tester a display refresh rate capability of approximately once every 200 milliseconds.

Data is accessed from DLC 3, terminal 2. It is triggered by a communication signal generated by the Diagnostic Tester when any OBD-II function has been selected.

On OBD-Il vehicles, the scan tool reads DTCs directly from the serial data stream, therefore, codes are displayed almost instantly. Codes can only be retrieved and displayed using the Diagnostic Tester or an equivalent J1978 scan tool.

SERIAL DATA


SERIAL DATA


Uses and Limitations of Scan Tool Serial Data for Diagnosis A scan tool is an exceptionally useful tool when diagnosing engine control system problems. It gives you access to vast quantities of information from a conveniently located diagnostic connector.

• A scan tool allows a "quick check" of sensors, actuators, and ECM calculated data. For example, when checking for sensor signals which may be shifted out of normal range, scan data allows you to quickly compare selected data to repair manual specifications or known good vehicle data.

• When checking for intermittent fault conditions, it provides an easy way to monitor input signals while wiring or components are manipulated, heated, and cooled.

There are, however, several important limitations you need to consider when attempting to diagnose certain types of problems using serial data.

• Serial data is processed information rather than a live signal. It represents what the ECM "thinks" it is seeing rather than the actual signal which would be measured at the ECM terminal. Serial data can also reflect a signal value the ECM has defaulted to, rather than the actual signal.

For example, with OBD, the Engine Coolant Temperature sensor data displayed with an open circuit is the failsafe value of 176’F. If the actual voltage was measured at the THW terminal of the ECM, it would be 5 volts, equivalent to -40'F.

SERIAL DATA


In the case of output commands, serial data represents the calculated output, not necessarily what the circuit driver is doing. For example, when cranking an engine which is in fuel cut failsafe (due to an open IGf line), calculated injection pulse is displayed on serial data even though the injector driver is not being operated.

Using serial data to troubleshoot intermittent problems also has its limitations because of data transmission speed.

When the data refresh rate is slow, as it is with slower baud rate data streams, it is easy to miss changes which occur in a signal between display updates. As a result, intermittent signal problems are often not detected on a slow serial data stream.

For example, a Throttle Position Sensor signal wire that goes open circuit every time the vehicle drives over a bump. If the open condition does not last for at least 1.25 seconds, there is a good possibility that the change in signal value will go undetected by your scan tool.

When troubleshooting intermittent problems on vehicles without high speed serial data (like Enhanced OBD-II), it is much better to use serial data generated by V-BoB than to use the OBD serial data. It takes more time to connect V-BoB to the ECM, but if an intermittent problem occurs, the high speed serial data generated by V-BoB will catch the fault.

Given this information, it is clear that care must be exercised when interpreting serial data and using it to make diagnostic decisions. Once you are familiar with irregularities like these, the risk of diagnostic error is significantly reduced.

SERIAL DATA


Serial Data InterpretationUsing and interpreting serial data may seem confusing at first because there is so much data. Some of the data uses unfamiliar names, and some of it is displayed in unfamiliar units. To help you become familiar with the new terminology and what each data parameter means, refer to appendices A & B of this handbook. They provide detailed definitions, specifications, and an explanation of each data parameter available on OBD, OBD-II, and V-BoB data streams.

ECM Strategy for Fuel and Spark Control Troubleshooting driveability problems can be complicated, especially when there is so much diagnostic data available. You may sometimes find it difficult to decide which information is important and which information you should ignore. The key is getting back to the basics. That means the basic theory and the basic data.

As you have learned, fuel and spark calculation are, for the most part, affected by only a few input sensors. In fact, basic injection and spark calculation are a function of just two sensors; the engine speed and engine load sensors.

There are only four other sensors which have significant effects on injection (and to a lesser degree on spark advance corrections); those are engine coolant temperature, intake air temperature, throttle angle, and oxygen sensor feedback.

Data analysis is much easier once you are familiar with these six input parameters, their units of display, and their nominal values.

Six Important Sensor Inputs The six major sensor inputs which have the most impact on fuel and spark calculations are, in order of importance:

• Engine Load - Vane Air Flow meter- Karman Vortex Air Flow meter- Mass Air Flow meter- Manifold Absolute Pressure sensor

• Engine Speed -Engine rpm (Ne) sensor

• Engine Coolant Temperature -Engine Coolant Temperature sensor

• Throttle Position - Throttle Position sensor- Closed Throttle Position switch

• Intake Air Temperature -Intake Air Temperature sensor

• Exhaust Oxygen: -02 Sensor

SERIAL DATA INTERPRETATION


Fuel TrimTo better understand how oxygen feedback and learned corrections are determined, a brief review of injection theory is in order.

Review of Injection Duration TheoryFinal fuel injection duration is a function of three steps:

• Basic injection duration • Duration corrections for operating conditions • Battery voltage correction

Basic injection duration is based on engine load, speed, and a correction factor called fuel trim. Duration corrections for operating conditions are based on the sensors listed below. These are adjustments to the basic injection duration based on changing operating conditions.

• Engine Coolant Temperature (ECT) • Throttle Position (TP) • Intake Air Temperature (IAT) • Exhaust Oxygen (02S)

Battery voltage correction is an adjustment to the final injection duration to account for variations in injector opening time caused by changing operating voltage.



Calculation of Basic Injection DurationThe first step in determining how much fuel to deliver to the engine is calculation of basic injection duration. Basic injection duration is a function of:

• Engine load (VAF, MAF, or MAP)• Engine speed (Ne)• Long fuel trim (LFT) correction factor

This basic injection duration value is the ECM's best guess at the actual injection time necessary to achieve an ideal air/fuel ratio. Generally, this basic injection calculation is very accurate, typically within ± 20% of what actual injection needs to be. Once within this range, the ECM can trim the air/fuel ratio to stoichiometry based on oxygen sensor information.

Oxygen Feedback CorrectionDepending on many different factors, the amount of correction required for 02S feedback will vary. If the amount of necessary correction remains relatively small, for example less than 10%, the ECM can easily adjust the mixture. As 02S feedback correction approaches the ± 20% limit, the ECM fuel correction range becomes limited.



Oxygen Feedback Correction ContinuedWhen the amount of necessary correction becomes excessive, the ECM has a "learned memory" to adjust or "trim" the basic injection calculation. By increasing or decreasing basic injection duration, 02S corrections can be held within an acceptable range, maintaining the ECM ability to correct over a wide air/fuel ratio range.

Fuel Trim Impact on Injection DurationFuel trim is a term used to describe the percentage of correction to injection duration based on oxygen feedback. There are two different fuel trim values which affect final injection duration; long fuel trim (Long FT) and short fuel trim (Short FT).

Long FT is part of the basic injection duration calculation. It is determined by how closely the fuel system achieves the design air/fuel ratio.

Long FT is a learned value which gradually changes in response to factors beyond the control of system design. For example, fuel oxygen content, engine wear, air leaks, variations in fuel pressure, and so forth.

Short FT is an addition to (or subtraction from) basic injection duration. Oxygen sensor information tells the ECM how close it comes to design air/ fuel ratio and the Short FT corrects for any deviation from this value.

How Short FT WorksShort FT is a temporary correction to fuel delivery which changes with every cycle of the oxygen sensor. Under normal conditions, it fluctuates rapidly around its ideal value of 0% correction and is only functional during closed loop operation.

Short FT is a parameter on the OBD-Il data stream, that can be displayed on the Diagnostic Tester. Its normal range is ± 20%, but under normal operating conditions, rarely goes beyond ± 10%.

Short FT responds to changes in 02S output. If basic injection duration results in a lean air/fuel ratio, Short FT responds with positive corrections (+1% to +20%) to add fuel or enrich the mixture. If basic injection is too rich, Short FT responds with negative corrections (-I% to -20%) to subtract fuel or enlean the mixture.

When Short FT is varying close to ± 0%, this indicates a neutral condition where the basic injection duration calculation is very close to stoichiometry, without any significant correction for 02S.



How Long FT WorksLong FT is a data parameter on the OBD and OBD-II data streams. It is a more permanent correction to fuel delivery because it is part of the basic injection duration calculation. Long FT changes slowly, in response to Short FT. Its normal range is ± 20%, positive values indicating rich correction and negative values indicating lean correction.

If Short FT deviates significantly from ± 10% for too long, the Long FT shifts, changing the basic injection duration. This shift in basic injection duration should bring Short FT back to the ± 10% range.

Unlike Short FT which effects injection duration calculation in closed loop only, the Long FT correction factor effects the basic injection duration calculation in open and closed loop. Because Long FT is stored in a nonvolatile RAM (NVRAM) and is not erased when the ignition is switched off, the fuel system is able to correct for variances in engine and fuel conditions even during warm-up and wide open throttle conditions.

On OBD data streams, Long FT is displayed as Target A/F. On non data stream equipped engines, Long FT is referred to as Learned Voltage Feedback (LVF) and can be accessed from the check connector VF1 terminal.

To gain a better understanding of Long and Short fuel trim, use the example given below. Referring to the graphic on the opposite page:

Condition #1shows a fuel system operating within normal design parameters. Based on engine load and speed, basic injection is calculated at 3.0 ins. The short FT is varying ± 10% and oxygen sensor voltage switching is normal.

Condition #2shows effects of air leak into intake. Basic injection remains at 3.0 ms because none of the inputs effecting basic injection duration have changed.

• Extra air causes engine to run lean, causing oxygen sensor to go lean.

• Short FT tries to correct but reaches +20% limit without bringing oxygen sensor back to normal switching.

• ECM learns that it will need to increase basic injection duration so that oxygen sensor can return to normal operating range.



Condition #3shows what happens after ECM shifts Long FT to +10%. Although MAF and rpm remain the same, basic injection increases by 10% based on shift in Long FT. Basic injection is now 3.3 ms.

• The fuel system is now supplying enough fuel to restore nearly normal oxygen sensor switching. Switching is taking place but the voltage swings are lower than normal. Short FT is still making an excessive correction (+15%) to achieve this.

• ECM learns that it must continue shifting Long FT to get Short FT back to ±10%.

Condition #4shows the result of another shift in Long FT. MAF and rpm are still the same as in condition #1, however, basic injection duration has increased by 20% to 3.6 ms.

• Basic injection is now back within ± 10% of required injection.

• Normal oxygen sensor switching is accompanied by Short FT switching ± 10% of basic injection duration.



Learned Voltage Feedback and Target Air Fuel RatioAlthough Long FT, Target A/F, and LVF (Learned Voltage Feedback) are essentially the same, there is a difference in how this data parameter is displayed on OBD engines. LVF and Target A/F are displayed as a voltage signal with a range of 0 to 5 volts. The signal, which varies in fixed 1.25 volt increments, has a nominal value of 2.50 volts.

When LVF is at 2.50 volts, it indicates that basic injection duration calculation is within ± 10% of required injection duration (to achieve 14.7 to 1 AFR). If basic injection duration deviates more than ± 10% of required injection, LVF will shift to correct the excessively lean or rich condition.

Lower voltage indicates decreased injection duration to correct for a rich condition. Higher voltage indicates increased injection duration to correct for a lean condition.



Using Fuel Trim in DiagnosisWhen troubleshooting driveability problems, one of the first checks to make is a quick inspection of the oxygen feedback system. Determine if the vehicle is operating in closed loop and if the fuel system is correcting for an excessively lean or rich operating condition.

When to Use Fuel Trim DataFuel trim value outside of prescribed operating range is not a problem in itself. This condition is typically an indication that other problems exist. Fuel trim data can help lead you to the causeof these problems. Typically you will use fuel trim data to:

• Perform a pre-diagnosis quick check of feedback control• Troubleshoot the cause of emissions system failure (I/M test failures)• Troubleshoot cause of driveability problems, particularly when these problems occur

during open loop operating modes (i.e. starting, warm-up, power enrichment) • Perform post-repair quick check of feedback control

Where to Find Fuel Trim DataThe easiest way to perform a fuel trim inspection is to use your Diagnostic Tester. Fuel trim data is available on all OBD-II and most OBD data streams. The following chart indicateswhat fuel trim data is available for diagnosis:



How to Determine Fuel System Loop StatusLong FT and LVF only "learns" during closed loop operation. Therefore, the engine must be operating in closed loop when performing tests involving fuel trim data. To confirm closed loop operation, refer to the following chart:

An alternate method of determining closed loop operation on all vehicles with DLC 1 (Check Connector) is to use your Diagnostic Tester to perform the 02S/rpm test. This test allows you to monitor the oxygen sensor(s) signal frequency and amplitude directly from the OX1 and OX2 terminals of DLC 1.



Sub-systems and Conditions Affecting Fuel TrimOnce you know the driveability symptom and are able to confirm that the air/fuel ratio is excessively lean or rich, it is a fairly easy task to identify all of the sub-systems which can effect the mixture. Check each sub-system to confirm proper operation.

The following chart lists sub-systems and other factors which can cause the oxygen feedback system to make rich or lean corrections and, in some cases, cause fuel trim data to approach its correction limits:

NOTE: OBD vehicles without High Altitude Compensation operating at high altitude (> 5000 feet) may operate at the lean fuel trim correction limit. This is a normal condition.



Introduction to Combustion ChemistryThe gasoline-powered internal combustion engine takes air from the atmosphere and gasoline, a hydrocarbon fuel, and through the process of combustion releases the chemical energy stored in the fuel. Of the total energy released by the combustion process, about 20% is used to propel the vehicle, the remaining 80% is lost to friction, aerodynamic drag, accessory operation, or simply wasted as heat transferred to the cooling system.

Modern gasoline engines are very efficient compared to predecessors of the late '60s and early '70s when emissions control and fuel economy were first becoming a major concern of automotive engineers. Generally speaking, the more efficient an engine becomes, the lower the exhaust emissions from the tailpipe. However, as clean as engines operate today, exhaust emission standards continually tighten. The technology to achieve these ever-tightening emissions targets has led to the advanced closed loop engine control systems used on today's Toyota vehicles. With these advances in technology comes the increased emphasis on maintenance, and when the engine and emission control systems fail to operate as designed, diagnosis and repair.

Understanding the Combustion ProcessTo understand how to diagnose and repair the emissions control system, one must first have a working knowledge of the basic combustion chemistry which takes place within the engine. That is the purpose of this section of the program.

The gasoline burned in an engine contains many chemicals, however, it is primarily made up of hydrocarbons (also referred to as HC. Hydrocarbons are chemical compounds made up of hydrogen atoms which chemically bond with carbon atoms. There are many different types of hydrocarbon compounds found in gasoline, depending on the number of hydrogen and carbon atoms present, and the way that these atoms are bonded.

Inside an engine, the hydrocarbons in gasoline will not burn unless they are mixed with air. This is where the chemistry of combustion begins. Air is composed of approximately 21% oxygen (02), 78% nitrogen (N2), and minute amounts of other inert gasses.

EMISSIONS #1 - COMBUSTION CHEMISTRY


The hydrocarbons in fuel normally react only with the oxygen during the combustion process to form water vapor (H2O) and carbon dioxide (CO2), creating the desirable effect of heat and pressure within the cylinder. Unfortunately, under certain engine operating conditions, the nitrogen also reacts with the oxygen to form nitrogen oxides (NOx), a criteria air pollutant.

The ratio of air to fuel plays an important role in the efficiency of the combustion process. The ideal air/fuel ratio for optimum emissions, fuel economy, and good engine performance is around 14.7 pounds of air for every one pound of fuel. This "ideal air/fuel ratio" is referred to as stoichiometry, and is the target that the feedback fuel control system constantly shoots for. At air/fuel ratios richer than stoichiometry, fuel economy and emissions will suffer. At air/fuel ratios leaner than stoichiometry, power, driveability and emissions will suffer.



Under "Ideal" Combustion ConditionsIn a perfectly operating engine with ideal combustion conditions, the following chemical reaction would take place:

• Hydrocarbons would react with oxygen to produce water vapor (H2O) and carbon dioxide (CO2)

• Nitrogen (N2) would pass through the engine without being affected by the combustion process. In essence, only harmless elements would remain and enter the atmosphere. Although modern engines are producing much lower emission levels than their predecessors, they still inherently produce some level of harmful emission output.

The Four-Stroke Combustion CycleDuring the Intake Stroke, air and fuel moves into the low pressure area created by the piston moving down inside the cylinder. The fuel injection system has calculated and delivered the precise amount of fuel to the cylinder to achieve a 14.7 to 1 ratio with the air entering the cylinder.

As the piston moves upward during the Compression Stroke, a rapid pressure increase occurs inside the cylinder, causing the air/fuel mixture to superheat. During this time, the antiknock property or octane rating of the fuel is critical in preventing the fuel from igniting spontaneously (exploding). This precise superheated mixture is now prime for ignition as the piston approaches Top Dead Center.



Just before the piston reaches top dead center to start the Power Stroke, the spark plug ignites the air/fuel mixture in the combustion chamber, causing a flame-front to begin to spread through the mixture. During combustion, hydrocarbons and oxygen react, creating heat and pressure. Ideally, the maximum pressure is created as the piston is about 8 to 12 degrees past top dead center to produce the most force on the top of the piston and transmit the most power through the crankshaft. Combustion by-products will consist primarily of water vapor and carbon dioxide if the mixture and spark timing are precise.

After the mixture has burned and the piston reaches bottom dead center, the Exhaust Stroke begins as the exhaust valve opens and the piston begins its return to top dead center. The water vapor, carbon dioxide, nitrogen, and a certain amount of unwanted pollutants are pushed out of the cylinder into the exhaust system.



Harmful Exhaust EmissionsAs previously mentioned, even the most modern, technologically advanced automobile engines are not "perfect"; they still inherently produce some level of harmful emission output. There are several conditions in the combustion chamber which prevent perfect combustion and cause unwanted chemical reactions to occur. The following are examples of harmful exhaust emissions and their causes.

Hydrocarbon (HC) EmissionHydrocarbons are, quite simply, raw unburned fuel. When combustion does not take place at all, as with a misfire, large amounts of hydrocarbons are emitted from the combustion chamber.

A small amount of hydrocarbon is created by a gasoline engine due to its design. A normal process called wall quenching occurs as the combustion flame front burns to the relatively cool walls of the combustion chamber. This cooling extinguishes the flame before all of the fuel is fully burned, leaving a small amount of hydrocarbon to be pushed out the exhaust valve.



Another cause of excessive hydrocarbon emissions is related to combustion chamber deposits. Because these carbon deposits are porous, hydrocarbon is forced into these pores as the air/fuel mixture is compressed. When combustion takes place, this fuel does not burn, however, as the piston begins its exhaust stroke, these hydrocarbons are released into the exhaust stream.

The most common cause of excessive hydrocarbon emissions is misfire which occurs due to ignition, fuel delivery, or air induction problems. Depending on how severe the misfire, inadequate spark or a noncombustible mixture (either too rich or too lean) will cause hydrocarbons to increase to varying degrees. For example, a total misfire due to a shorted spark plug wire will cause hydrocarbons to increase dramatically. Conversely, a slight lean misfire due to a false air entering the engine, may cause hydrocarbons to increase only slightly.

Excess hydrocarbon can also be influenced by the temperature of the air/ fuel mixture as it enters the combustion chamber. Excessively low intake air temperatures can cause poor mixing of fuel and air, resulting in partial misfire.



Carbon Monoxide (CO) EmissionCarbon monoxide (CO) is a byproduct of incomplete combustion and is essentially partially burned fuel. If the air/fuel mixture does not have enough oxygen present during combustion, it will not bum completely. When combustion takes place in an oxygen starved environment, there is insufficient oxygen present to fully oxidize the carbon atoms into carbon dioxide (CO2). When carbon atoms bond with only one oxygen atom carbon monoxide (CO) forms.

An oxygen starved combustion environment occurs as a result of air/fuel ratios which are richer than stoichiometry (14.7 to 1). There are several engine operating conditions when this occurs normally. For example, during cold operation, warm-up, and power enrichment. It is, therefore, normal for higher concentrations of carbon monoxide to be produced under these operating conditions. Causes of excessive carbon monoxide includes leaky injectors, high fuel pressure, improper closed loop control, etc.



When the engine is at warm idle or cruise, very little carbon monoxide is produced because there is sufficient oxygen available during combustion to fully oxidize the carbon atoms. This results in higher levels of carbon dioxide (CO2) the principal by-product of efficient combustion.

Oxides of Nitrogen (NOx) EmissionHigh cylinder temperature and pressure which occur during the combustion process can cause nitrogen to react with oxygen to form Oxides of Nitrogen (NOx). Although there are various forms of nitrogen-based emissions that comprise Oxides of Nitrogen (NOx), nitric oxide (NO) makes up the majority, about 98% of all NOx emissions produced by the engine.

Generally speaking, the largest amount of NOx is produced during moderate to heavy load conditions when combustion pressures and temperatures are their highest. However, small amounts of NOx can also be produced during cruise and light load, light throttle operation. Common causes of excessive NOx include faulty EGR system operation, lean air/fuel mixture, high temperature intake air, overheated engine, excessive spark advance, etc.



Air/Fuel Mixture Impact on Exhaust EmissionsAs you can see in the graph above, HC and CO levels are relatively low near the theoretically ideal 14.7 to 1 air/fuel ratio. This reinforces the need to maintain strict air/fuel mixture control. However, NOx production is very high just slightly leaner than this ideal mixture range. This inverse relationship between HC/CO production and NOx production poses a problem when controlling total emission output. Because of this relationship, you can understand the complexity in reducing all three emissions at the same time.



Exhaust Analysis Using 4 and 5 Gas Analyzers So far we've discussed how harmful exhaust emissions are produced during combustion. However, in addition to these harmful emissions, both carbon dioxide (CO2) and oxygen (O2) readings can provide additional information on what's going on inside the combustion chamber.

Carbon Dioxide (CO2)Carbon dioxide, or CO2, is a desirable byproduct that is produced when the carbon from the fuel is fully oxidized during the combustion process. As a general rule, the higher the carbon dioxide reading, the more efficient the engine is operating. Therefore, air/fuel imbalances, misfires, or engine mechanical problems will cause CO2 to decrease. Remember, "ideal" combustion produces large amounts Of CO2 and H2O (water vapor).

EMISSIONS #2 - EMISSION ANALYSIS


Oxygen (O2)Oxygen (O2) readings provide a good indication of a lean running engine, since O2 increases with leaner air/fuel mixtures. Generally speaking, O2 is the opposite of CO, that is, O2 indicates leaner air/fuel mixtures while CO indicates richer air/fuel mixtures. Lean air/fuel mixtures and misfires typically cause high O2 output from the engine.

Other Exhaust EmissionsThere are a few other exhaust components which impact driveability and/or emissions diagnosis, that are not measured by shop analyzers. They are:

• Water vapor (H2O) • Sulfur Dioxide (SO2) • Hydrogen (HO • Particulate carbon soot (C)

Sulfur dioxide (SO2) is sometimes created during the combustion process from the small amount of sulfur present in gasoline. During certain conditions the catalyst oxidizes sulfur dioxide to make SO3, which then reacts with water to make H2SO4 or sulfuric acid. Finally, when sulfur and hydrogen react, it forms hydrogen sulfide gas. This process creates the rotten egg odor you sometimes smell when following vehicles on the highway. Particulate carbon soot is the visible black "smoke you see from the tailpipe of a vehicle that's running very rich.



Causes of Excessive Exhaust Emissions As a general rule, excessive HC, CO, and NOx levels are most often caused by the following conditions:

• Excessive HC results from ignition misfire or misfire due to excessively lean or rich air/fuel mixtures

• Excessive CO results from rich air/fuel mixtures• Excessive NOx results from excessive combustion temperatures

There are lesser known causes to each of these emissions that will be discussed later. When troubleshooting these types of emissions failures, you will be focusing on identifying the cause of the conditions described above. For example, to troubleshoot the cause of excessive CO emissions, you need to check all possible causes of too much fuel or too little air (rich air fuel/ratio). The following lists of causes will help familiarize you with the sub-systems most often related to excessive CO, HC and NOx production.

Causes of Excessive HydrocarbonsAs mentioned, high hydrocarbons is most commonly caused by engine misfires. The following list of problems could cause high HC levels on fuel injected vehicles. As with any quick reference, there are other less likely causes that may not be included in the list. Here are some of the more common causes:

• Ignition system failures -faulty ignition secondary component-faulty individual primary circuit on distributorless ignition system -weak coil output due to coil or primary circuit problem

• Excessively lean air/fuel mixture - leaky intake manifold gasket- worn throttle shaft

• Excessive EGR dilution - EGR valve stuck open or excessive EGR flow rate- EGR modulator bleed plugged

• Restricted or plugged fuel injector(s)

• Closed loop control system incorrectly shifted lean

• False input signal to ECM -incorrect indication of load, coolant temp., O2 content, or throttle position

• Exhaust leakage past exhaust valve(s) - tight valve clearances- burned valve or seat

• Incorrect spark timing - incorrect initial timing- false input signal to ECM



• Excessive combustion blowby - worn piston rings or cylinder walls

• Insufficient cylinder compression

• Carbon deposits on intake valves

Causes of Excessive Carbon MonoxideHigh carbon monoxide levels are caused by anything that can make the air/mixture richer than "ideal". The following examples are typical causes of rich mixtures on fuel injected vehicles:

• Excessive fuel pressure at the injector(s)

• Leaking fuel injector(s)

• Ruptured fuel pressure regulator diaphragm

• Loaded/malfunctioning EVAP system (two speed idle test)

• Crankcase fuel contamination (two speed idle test)

• Plugged PCV valve or hose (two speed idle test)

• Closed loop control system incorrectly shifted rich

• False input signal to ECM -incorrect indication of load, coolant temp., O2 content, or throttle position

Note: It should be pointed out that due to the reduction ability of the catalytic converter, increases in CO emissions tend to reduce NOx emissions. It is not uncommon to repair a CO emissions failure and, as a result of another sub-system deficiency, have NOx increase sufficiently to fail a loaded-mode transient test.



Causes of Excessive Oxides of NitrogenExcessive oxides of nitrogen can be caused by anything that makes combustion temperatures rise. Typical causes of high combustion temperature on fuel injected vehicles include:

• Cooling system problems - insufficient radiator airflow - low coolant level - poor cooling fan operation - thermostat stuck closed or restricted - internal radiator restriction

• Excessively lean air/fuel mixture - leaky intake manifold gasket - worn throttle shaft

• Closed loop control system incorrectly shifted lean

• Improper oxygen sensor operation - slow rich to lean switch time - rich biased 02 sensor voltage

• Improper or inefficient operation of EGR system - restricted EGR passage - EGR valve inoperative - EGR modulator inoperative - plugged E or R port in throttle body - faulty EGR VSV operation - leaky/misrouted EGR hoses

• Improper spark advance system operation - incorrect base timing - false signal input to ECM - improper operation of knock retard system

• Carbon deposits on intake valves



Evaporative EmissionsUp to now, we've only discussed the creation and causes of tailpipe or exhaust emission output. However, it should be noted that hydrocarbon (HC) emissions come from the tailpipe, as well as other evaporative sources, like the crankcase, fuel tank and evaporative emissions recovery system.

In fact, studies indicate that as much as 20% of all HC emissions from automobiles comes from the fuel tank and carburetor (on carbureted vehicle, of course). Because hydrocarbon emissions are Volatile Organic Compounds (VOCs) which contribute to smog production, it is just as important that evaporative emission controls are in as good a working order as combustion emission controls.

Fuel injected vehicles use an evaporative emissions system to store fuel vapors from the fuel tank and burn them in the engine when it is running. When this system is in good operating order, fuel vapor cannot escape from the vehicle unless the fuel cap is removed. The subject of Evaporative Emissions Systems is addressed in the next section of this program.



Diagnosis Using an Exhaust Gas AnalyzerUse of a four or five gas exhaust analyzer can be helpful in troubleshooting both emissions and driveability concerns. Presently, shop grade analyzers are capable of measuring from as few as two exhaust gasses, HC and CO, to as many as five. The five gasses measured by the latest technology exhaust analyzers are: HC, CO, CO2, O2 and NOx. Remember, HC, CO, CO2, and NOx are measured in Enhanced I/M programs.

All five of these gasses, especially O2 and CO2, are excellent troubleshooting tools. Use of an exhaust gas analyzer will allow you to narrow down the potential cause of driveability and emissions concerns, focus your troubleshooting tests in the area(s) most likely to be causing the concern, and save diagnostic time. In addition to helping you focus your troubleshooting, an exhaust gas analyzer also gives you the ability to measure the effectiveness of repairs by comparing before and after exhaust readings.

In troubleshooting, always remember the combustion chemistry equation: Fuel (hydrogen, carbon, sulfur) + Air (nitrogen, oxygen) = Carbon dioxide + water vapor + oxygen + carbon monoxide + hydrocarbon + oxides of nitrogen + sulfur oxides

In any diagnosis of emission or driveability related concern, ask yourself the following questions:

• What is the symptom?

• What are the "baseline" exhaust readings? At idle, 2500 rpm, acceleration, deceleration, light load cruise, etc.

• Which sub-system(s) or component(s) could cause the combination of exhaust gas readings measured?



The Effects of Secondary AirSome Toyota engines use a secondary air system to supplement the oxygen supply for the oxidation catalyst. This supplementary air is introduced into the exhaust stream upstream of the catalytic converter. Secondary air increases the oxygen content of the exhaust stream and reduces the carbon dioxide by diluting it.

Analyzing Exhaust Emission Readings

• Hydrocarbons are measured by an exhaust analyzer in parts per million (ppm). As you know, HC is unburned fuel that remains as a result of a misfire. When combustion doesn't take place or when only part of the air/fuel charge burns, hydrocarbon levels goes up.

• Carbon Monoxide is measured by an exhaust analyzer in percent (%) or parts per hundred. CO is a byproduct of combustion, therefore, if combustion does not take place, carbon monoxide will not be created. Based on this premise, when a misfire occurs, the carbon monoxide that would have normally been produced during the production process is not produced. Generally speaking, on fuel injected vehicles, high CO means too much fuel is being delivered to the engine for the amount of air entering the intake manifold.

• Nitrogen Oxides measured by an exhaust analyzer in parts per million (ppm). Nitrogen oxides are a by-product of combustion. NOx is formed in large quantities when combustion temperatures exceed about 2500' F. Anything which causes combustion temperatures to rise will also cause NOx emissions to rise. Misfire can also cause NOx to rise because of the increase in oxygen that it causes in the catalytic converter feed gas.

• Carbon Dioxide measured by an exhaust analyzer in percent (%) or parts per hundred. Carbon dioxide is a by-product of efficient and complete combustion. Near perfect combustion will result in carbon dioxide levels which approach the theoretical maximum of 15.5%. Carbon dioxide levels are effected by air/fuel ratio, spark timing, and any other factors which effect combustion efficiency.



• Oxygen is measured by an exhaust analyzer in percent (%) or parts per hundred. The amount of oxygen produced by an engine is effected by how close the air/fuel ratio is to stoichiometry. As the mixture goes lean of stoichiometry, oxygen increases. As mixture goes rich of stoichiometry, oxygen falls close to zero. Because oxygen is used up in the combustion process, concentrations at the tailpipe will be very low. If misfire occurs, however, oxygen will increase dramatically as it passes unused through the combustion chamber.

Another factor in analyzing NOx emissions are the two primary emissions sub-systems designed to control NOx levels, the EGR and reduction catalyst systems. NOx emissions will increase when the EGR system malfunctions or when the reduction catalyst efficiency falls. Efficiency of the reduction catalyst is closely tied to normal operation of the closed loop fuel control system. Reduction efficiency falls dramatically when catalyst feed gas carbon monoxide content is too low (oxygen content too high.)



Pre-Catalyst Versus Post-Catalyst TestingWhen using an exhaust analyzer as a diagnostic tool, it is important to remember that combustion takes place twice before reaching the tailpipe. First, primary combustion takes place in the engine. This determines the composition of catalyst feed gas, which dramatically effects catalyst efficiency. When the exhaust gases reach the three-way catalytic converter, two chemical processes occur.

Catalyst ReductionFirst, nitrogen oxide gives up its oxygen. This only occurs when a sufficient amount of carbon monoxide is available for the oxygen to bond with. This chemical reaction results in reduction of nitrogen oxide to pure nitrogen and oxidation of the carbon monoxide to form carbon dioxide.

Catalyst OxidationSecond, hydrocarbon and carbon monoxide continue to burn. This occurs only if there a sufficient amount of oxygen available for the hydrogen and carbon to bond with. This chemical reaction results in oxidation of hydrogen and carbon to form water vapor (H2O) and carbon dioxide (CO2).



Examples of Deceiving Post-Catalytic AnalysisWhen troubleshooting an emissions failure, your primary concern will be what comes out of the tailpipe. In other words, it doesn't matter whether the efficient burn occurred in the engine or the catalyst. However, when troubleshooting a driveability concern, the catalytic converter may mask important diagnostic clues which can be gathered with your exhaust analyzer. The following are examples of situations where post-catalyst reading may be deceiving.

• Example 1: A minor misfire under load is causing a vehicle to surge. The exhaust gas from the engine would show an increase in HC and O2, and a reduction in CO2. However, once this exhaust gas reaches the catalytic converter, especially a relatively new and efficient catalyst, the oxidation process will continue. The excess HC will be oxidized, causing HC and O2 to fall, and CO2 to increase. At the tailpipe, the exhaust readings may look perfectly normal.

In this example, it is interesting to note that NOx readings will increase because of the reduced carbon monoxide and increased oxygen levels in the catalyst feed gas. This could be detected with a five gas analyzer.



• Example 2: A small exhaust leak upstream of the exhaust oxygen sensor is causing a false lean indication to the ECM. This resulted in excessively rich fuel delivery to bring oxygen sensor voltage back to normal operating range. The customer concern is a sudden decrease of 20% in fuel economy.

• Example 3: A restriction in the fuel return line elevates pressure causing an excessively rich air/fuel ratio and a 20% decrease in fuel economy. Although carbon monoxide emissions from the engine are elevated as a result of this rich air/fuel ratio, the catalytic converter is able to oxidize most of it into carbon dioxide. The resulting tailpipe readings appear to be normal, except for oxygen, which is extremely low for two reasons. First, the increase in CO caused a proportionate decrease in O2 in the converter feed gas. Second, the little oxygen left over was totally consumed oxidizing the CO into CO2.

Based on this example, you can see that oxygen is a better indicator of lean or rich air/fuel ratios than carbon monoxide when testing post catalytic converter.



General Rules of Emission Analysis• If CO goes up, O2 goes down, and conversely if O2 goes UP, CO goes down.

Remember, CO readings are an indicator of a rich running engine and O2 readings are an indicator of a lean running engine.

• If HC increases as a result of a lean misfire, O2 will also increase

• CO2 will decrease in any of the above cases because of an air/fuel imbalance or misfire

• An increase in CO does not necessarily mean there will be an increase in HC. Additional HC will only be created at the point where rich misfire begins (3% to 4% CO)

• High HC, low CO, and high O2 at same time indicates a misfire due to lean or EGR diluted mixture

• High HC, high CO, and high O2 at same time indicates a misfire due to excessively rich mixture.

• High HC, Normal to marginally low CO, high O2, indicates a misfire due to a mechanical engine problem or ignition misfire

• Normal to marginally high HC, Normal to marginally low CO, and high O2 indicates a misfire due to false air or marginally lean mixture



To verify that the exhaust readings are not being diluted in the exhaust system or analyzer sampling point, combine the CO reading with the CO2 reading. An undiluted sample should always have a sum of greater than 6%. Remember, the secondary air system may be diluting the sample if it is not disabled during analysis. In fact, engines with secondary air injection systems will have relatively high oxygen concentrations in the exhaust because of the extra air pumped into the exhaust, post combustion.

Factors That Degrade Emissions & DriveabilityThe following major factors contribute to the overall increase in exhaust emissions levels and degraded vehicle driveability:

• Lack of scheduled maintenance- Sub-system failures- Combination of multiple marginal sub-systems

• Tampering- Removal of emissions sub-system equipment- Modification of engine/emissions sub-systems

• Use of leaded fuels or incompatible additives in closed loop control systems



Engine MechanicalThe engine control and emissions sub-systems all rely on good mechanical condition of the engine to operate normally and effectively. Mechanical malfunctions effect exhaust emissions and driveability, both directly and indirectly:

• Directly, any mechanical malfunction will likely cause significant increases in exhaust emissions by causing misfire, allowing combustion gasses to escape past exhaust valves or piston rings, by altering air/fuel ratios, or any number of other possibilities.

• Indirectly, mechanical malfunctions change the composition of catalyst feed gas, preventing the catalytic converter from operating efficiently.

Examples of mechanical problems that can increase exhaust emission output include; low cylinder compression causing poor combustion and/or misfire, worn oil control rings that allow excessive engine oil (HC) to be consumed during combustion, etc. Remember, always check the integrity of basic engine mechanical systems before moving on to more complex engine or emission sub-systems.

Air Induction SystemThe air induction sub-system meters and measures engine air based on driver demand. In the event that unmetered air enters the engine or if it is not measured accurately, the unbalanced air /fuel ratio will cause increases in exhaust emissions and/or driveability concerns. The following areas of the air induction system may require your attention when troubleshooting an emissions or driveability concern.

EMISSION SUB SYSTEMS - Engine & Emission Systems


False Intake Air EntryIf unmeasured air enters engines equipped with L-type injection, they may exhibit lean surges, misfire and rough idle. Lean operating conditions can also cause increases in hydrocarbons, due to misfire, and in NOx due to leaner air/fuel ratios, increased combustion temperatures and decreased reduction catalyst efficiency.

Engines equipped with D-type injection will exhibit an elevated engine idle speed if unmeasured air enters the induction system. Generally, this will not cause exhaust emissions to increase significantly.

Intake Valve DepositsIntake valve deposits are hardened carbon deposits which form on the back side of the intake valve. The degree of deposits vary depending on many factors like fuel properties, driving habits, and engine family. Intake valve deposits can cause driveability concerns as well as increased exhaust emissions.

Excessive intake valve deposits can cause an engine to run excessively lean while cruising and accelerating, and excessively rich during deceleration. During lean operating periods, NOx emissions are elevated. During rich operating periods, CO emissions are elevated. The amount of emissions increase has a linear relationship with the degree of deposits on the valves. At some point, deposits can effect emissions enough to put a vehicle out of compliance in an Enhanced I/M test.



Effects of Intake Valve Deposits on DriveabilityThere are several common driveability symptoms which can be caused by intake valve deposits; stumble, hesitation and loss of power under load. Stumble and hesitation, especially when the engine is cold, are by far the most common problems caused by excessive intake valve deposits. The porous carbon deposits act like a sponge, absorbing enough fuel vapor to cause these symptoms.

Severe carbon deposits can also cause a loss of power at high engine rpm. When deposits accumulate sufficiently to restrict airflow through the intake valve, the volumetric efficiency of the engine is effected, causing the engine to loose power.

The best way to confirm excessive deposits is to visually inspect the valves using a borescope. If repairs are necessary, equipment is available to clean the valves without removing the cylinder head. Refer to Toyota Technical Service Bulletins for more information on procedures and special service tools.



Fuel Delivery SystemThe fuel delivery and injection control system delivers fuel to the engine and meters the amount of fuel which is injected into the intake manifold. There are two factors which, under normal conditions, should determine the air/fuel ratio; fuel pressure and injection duration. In the event that either of these factors is incorrect, normal air/fuel ratio will be upset.

One factor which can upset the normal air/fuel ratio is unmeasured fuel. Leaking injectors, a leaking fuel pressure regulator diaphragm, crankcase oil diluted with gasoline, or a saturated evaporative emissions system can all cause an excessively rich air/fuel ratio.

Finally, the air fuel ratio can also be upset by restriction in the injector nozzle or problems with the injector spray pattern. Symptoms caused by fuel injector spray pattern and restrictions are similar to those caused by intake valve deposits; stumble, hesitation, loss of power, etc.



Fuel Injector Test MethodsTesting fuel injectors for restriction and/or spray pattern can be accomplished one of two ways; visual inspection and pressure drop method.

Visual InspectionVisual inspection requires that the suspect injector(s) be removed from the engine, connected to a test apparatus, and electrically energized for a fixed time period. The injector should deliver the specified volume and spray pattern should appear uniformly conical.

Pressure Drop TestThe pressure drop method requires the use of a fuel pressure gauge and an injector pulse timer available from specialty tool vendors. Generally speaking, this test can be performed without removing the injector from the engine. By energizing the injector for a fixed pulse width and observing the pressure drop on the fuel system, the relative fuel flow can be compared for each injector. If all injectors exhibit a consistent pressure drop, it follows that all injectors are flowing the same volume of fuel. There are three shortcomings with this type of test which limit its usefulness, they are:

• Actual injector flow volume can not be determined, only relative flow

• Spray pattern cannot be observed during this test

• There are no specifications for the pressure drop test.



Incorrect Injection DurationIn addition to the problems mentioned above, false sensor input from any of the six major input sensors can also cause the air/fuel ratio to shift sufficiently to cause driveability and/or emissions concerns. If engine load is incorrectly calculated, fuel requirements are also miscalculated, resulting in a driveability or emissions concern. This type of a condition can be identified by reading sensor signals and comparing them to standard values. With this type of condition, the ECM adaptive fuel program will probably be making major corrections to bring the air/fuel ratio back into a neutral range (stoichiometry).

The best way to confirm that a neutral air/fuel ratio is being delivered to the engine, is to monitor the adaptive fuel correction to injection duration. This can be accomplished several different ways, depending on the engine being tested:

1. OBD vehicles without serial data: Use a voltmeter on terminal VF1 at DLC 1 (check connector)

2. OBD vehicles with serial data: Use a scan tool to monitor Target A/F data

3. OBD-II vehicles: Use a scan tool to monitor Fuel Trim data



A Few Words on FuelEffects of Octane Rating on Engine Performance and "Knocking"When diagnosing any customer concern related to poor engine performance or engine "knocking", always suspect fuel quality, or more specifically the octane rating of the fuel being used. The octane rating is a reflection of the fuel's ability to withstand engine knock, and is rated by its Antiknock Index (or pump octane rating). This number is displayed on a yellow sticker on the side of each gas pump.

Since octane requirements differ from vehicle to vehicle, always check in the Owner's Manual for vehicle's exact octane requirement and verify with the customer that their concern is not the result of low octane fuel. On vehicles with Knock Control systems, low octane may not cause the engine to knock, since the system has the ability to retarded spark advance; however, the engine may perform poorly as a result of a conservative spark advance strategy. If the engine knocking or performance concern is not the result of a sub-system problem, you may want to suggest to the customer a change in fuel grade or retailer.

Gasoline Volatility and Seasonal Fuel BlendsVolatility refers to a fuel's ability to change from a liquid to a vapor. This characteristic of fuel is very important in maintaining satisfactory vehicle driveability. If fuel volatility is too low, hard starting and poor warm-up driveability problems may result. If fuel volatility is too high, vapor lock, hot driveability problems, and excessive evaporative emissions may result.

Since fuel vaporization is naturally sensitive to ambient temperature change, refiners typically provide a more volatile fuel blend in the winter to provide easy start-up and cold weather driveability. Conversely, in the summer, a less volatile fuel blend is provided to lessen the chance of vapor lock or hot driveability problems.

Occasional driveability concerns may arise when retailers change blends between seasons (typically spring or fall). For example, if a change was made to a winter blend, yet the weather remained uncharacteristically hot, a hot driveability problem may arise (and vice versa).

Oxygenated FuelsAs a result of the 1990 Clean Air Act Amendments, the use of oxygenated and reformulated fuels has already occurred in many metropolitan areas across the United States. Oxygenated gasoline contain oxygen carrying compounds (usually ethanol or MTBE) that chemically enleans the AT mixture. This leaner AT mixture results in lower carbon monoxide (CO) emissions from the tailpipe.

A few points require clarification concerning oxygenated fuels. First, late model feedback control vehicles may see a slight fuel economy loss (around 2%) when using oxygenated fuels. This occurs as a result of feedback system enrichening the mixture when the O2 sensor detects the additional oxygen provided by the fuel. Second, fuel system components in older model vehicles may experience swelling (hoses, O-rings, gaskets, etc.) from the alcohol used in some oxygenated fuels. The Owner's Manual contains detailed information on the allowable percentages of both MTBE and ethanol.



Emission Control Sub-Systems

Closed Loop Feedback Control SystemThe heart of the emissions control system is the closed loop fuel feedback control system. It is responsible for controlling the content of the catalytic converter feed gas and ultimately determines how much HC, CO and NOx leaves the tailpipe. The closed loop control system works primarily during idle and cruise operations and makes adjustments to injection duration based on signals from the exhaust oxygen sensor.

During closed loop operation, the ECM keeps the air/fuel mixture modulated around the ideal 14.7 to 1 air/fuel ratio (stoichiometry). By precisely controlling fuel delivery, the oxygen content of the exhaust stream is held within a narrow range that supports efficient operation of the three-way catalytic converter. However, if the air/fuel ratio begins to deviate from its preprogrammed swings, catalyst efficiency falls dramatically, especially the reduction of NOx.

EMISSION SUB SYSTEMS - Closed Loop Feedback Control System


Closed Loop OperationWhen the ECM has determined conditions suitable for entering closed loop operation (based on many sensor values), it uses the oxygen sensor signal to determine the exact concentration of oxygen in the exhaust stream. From this signal, the ECM determines whether the mixture is richer (low 02) or leaner (high 02) than the ideal 14.7 to I air/fuel ratio:

• If the oxygen sensor signal is above 0.45 volt, the ECM determines that the air/fuel mixture is richer than ideal and decreases the injection duration.

• If the oxygen sensor signal is below 0.45 volt, the ECM determines that the air/fuel mixture is leaner than ideal and increases the injection duration.

During normal closed loop operation, the oxygen sensor signal switches rapidly between these two conditions, at a rate of more than 8 cycles in 10 seconds at 2500 rpm. Small injection corrections take place each time the signal switches above and below the 0.45 threshold voltage.



Closed loop control works on the premise of the command changing the condition and can be summarized as follows:

• 02S indicates rich = ECM commands leaner injection duration

• 02S indicates lean = ECM commands richer injection duration

In short, the oxygen sensor informs the ECM of needed adjustments to injector duration based on exhaust conditions. After adjustments are made, the oxygen sensor monitors the correction accuracy and informs the ECM of additional adjustments. This monitor/command cycle occurs continuously during closed loop operation in an effort to keep the air/fuel mixture modulated around the ideal ratio.



Open Loop Operating ConditionsThere are certain operating conditions that require the mixture to be richer or leaner than ideal. During these conditions the ECM ignores the oxygen sensor signal and controls fuel duration using other sensor information. This operation, called Open Loop, typically occurs during engine start "clock out", cold engine operation, acceleration, deceleration, moderate to heavy load conditions, and wide open throttle (WOT).

Effects of Incorrect Closed Loop Control on Emissions and DriveabilityGenerally, incorrect fuel control affects emissions and driveability as follows:

• Air/fuel ratio too rich may result in emissions failure for CO and HC, rich misfire, engine stalling, rough idle, hesitation, overheated converter, etc.

• Air/fuel mixture too lean may result in failure for HC and NOx, lean misfire, engine stalling, stumble, flat spot, hesitation, rough idle, poor acceleration, etc.



Closed Loop Control System Functional ChecksIf you suspect that the closed loop system is not properly controlling fuel delivery, one of the first checks you should perform is an Oxygen (02) Sensor signal check. Since the ECM relies on the 02S signal to fine tune injection duration during closed loop operation, an accurate check of the 02S signal is crucial in diagnosing problems that you suspect are the result of improper closed loop control.

Remember, the engine (and engine control system) must meet certain conditions prior to checking the 02S signal or your results may be inaccurate. This usually means that the engine and 02 sensor must reach operating temperature, the feedback system is in closed loop, and engine speed is maintained at a specified rpm. 02S signal checks can be performed on OBD/OBD-II vehicles by using the Diagnostic Tester. Older vehicles may require you to backprobe the 02S signal wire using the Autoprobe or digital multimeter.

Oxygen Sensor (02S) Signal ChecksMonitoring oxygen sensor signal switching frequency and amplitude is the key to a quick functional test of the entire closed loop control subsystem. The check can be performed as follows:

• Start engine and allow it reach operating temperature

• Make sure all accessories are off

• Run engine at 2500 rpm for at least two minutes to ensure 02 sensor is at normal operating temperature

• 02S signal frequency should be at least eight cycles in ten seconds (0.8 hz) in order to ensure efficient catalyst operation.

• Also, signal amplitude should consistently exceed 550 mv on the rich swing and fall below 400 mv on the lean swing. If the sensor is degraded, either signal frequency or amplitude or both will be effected.



02S Check Using AutoprobeIf the Autoprobe feature of the Diagnostic Tester is used, set up the oscilloscope to read the 02S signal. Follow these steps:

• Calibrate the Autoprobe

• Set time to 1 sec/div (use 0.2 sec/div when measuring switch time)

• Set volts to 0.2 v/div

• Set trigger to automatic

• Use the single shot trigger to capture and freeze the signal

02S Check Using a Digital MultimeterIf a digital multimeter (DMM) is used, like the Fluke 80 series, set up the meter as follows:

• DC volts • Select the MIN/MAX feature• Press the MIN/MAX button to toggle between maximum, minimum, and average signal

voltage

Tests can be performed by connecting your test instrument to the OX1 / OX2 terminal of DLC1, or by back probing directly at the oxygen sensor connector.

Many factors can contribute to the degradation of the oxygen sensor including age and contamination. Since this topic relates closely with catalytic converter operation, it will be discussed in detail later.



Closed Loop Control Quick CheckIf you suspect that the ECM is not responding correctly to the oxygen sensor signal, a quick check of the closed loop system can be made by artificially driving the system rich or lean and observing the corresponding change in closed loop fuel control. This check can be performed as follows:

• Temporarily remove the fuel pressure regulator signal hose and plug it, to create a rich condition. The ECM should respond by commanding the injectors to lean the mixture.

• Temporarily create an intake manifold vacuum leak to make a lean condition. The ECM should respond by commanding the injectors to enrich the mixture.

On vehicles with serial data, changes to 02S signal, fuel trim, and injection duration can be observed using the Diagnostic Tester.

CAUTION: When performing this type of check, avoid prolonged mixture imbalances (both lean or rich) for any extended length of time, as this may cause the catalyst to overheat and permanently damage the converter.



Closed loop control has the ability to provide approximately ± 20% correction range from the basic fuel calculation. This allows the system to easily compensate for small mixture imbalances; however, major air/fuel imbalances (such as large vacuum leaks, leaky fuel pressure regulator, etc.) may push its correction abilities to the limit without bringing the air/fuel mixture back to the "ideal" ratio. If this occurs, whether the mixture is driven too rich or too lean, increased emission levels and driveability problems may result from the systems inability to correct for these problems.

Check For Major Fuel CorrectionA quick check of the adaptive fuel correction will show the ECM's intentions of correcting this condition. Depending on the model, this adaptive correction factor may be called VF Voltage, Target AN, or Long-Term Fuel Trim, and on serial data equipped vehicles may be checked using the Diagnostic Tester.



Spark Advance ControlThe Spark Advance Control system maximizes engine efficiency by continuously adjusting spark advance timing to deliver peak combustion pressures when the piston reaches about 10' after TDC. Incorrect spark timing can have a significant effect on emission output and vehicle driveability. If ignition timing is excessively advanced during certain conditions, detonation will occur resulting in increased HC and NOx levels. Since NOx production is most predominant under loaded engine operating conditions, the spark advance system must ensure accurate ignition timing during these conditions. If ignition timing is incorrectly retarded, only partial combustion will take place resulting poor engine performance and increased emission levels.

Causes of Incorrect Spark TimingOn systems that use the ECM to compute ignition spark advance, there are only two conditions which are likely to cause spark timing to be incorrect; initial timing or a false input signal to the ECM.

The first step in troubleshooting emissions and driveability concerns should always include a quick check of initial ignition timing. Any error in initial timing will be reflected throughout the entire spark advance curve.

If engine load is miscalculated because of incorrect input signals, spark advance angle will not be appropriate for engine operating conditions. This will result in driveability and emission problems. Refer to course 850 for additional information on spark advance strategy.

ENGINE SUB SYSTEMS - Spark Advance Control


The Effects of Fuel OctaneToyota engines equipped with a knock detection system are very sensitive to fuel octane levels. Motor fuels with low octane ratings will cause the engine to detonate, which will in turn, cause the detonation retard system to retard timing. On some vehicles with advanced ECM operating strategies, an adaptive memory factor is used to track signals from the knock sensor. When detonation occurs frequently, the ECM relearns the basic spark advance curve, retarding spark throughout the entire engine operating range. This retarded spark curve will negatively effect engine performance and fuel economy under all driving conditions, even after a tank of higher octane fuel is purchased. The retarded spark curve will remain stored in the ECM keep alive memory until the engine is operated for a substantial amount of time on the higher octane fuel, or until the "keep alive memory" is cleared by removing power from the BATT terminal.

Purpose of Spark Advance Control SystemsThe amount of spark advance needed by the engine varies depending on a number of different operating conditions. Generally, spark advance follows the following strategy:

• spark advance increases with higher engine speeds for performance and fuel economy.

• spark advance needs to decrease under heavy load conditions to avoid detonation.

They are many variables the system must consider when determining the proper spark lead time. Coolant temperature, fuel quality, and engine load are just a few of the many factors that can significantly impact ideal ignition time. The ECM determines proper spark timing by applying various input signals against a preprogrammed spark advance strategy or "map".

Fuel injected Toyota vehicles use either a mechanical or electronic spark advance control system. They are referred to as either conventional EFI ignition system (mechanical), Variable Advance Spark Timing (VAST) or Electronic Spark Advance (ESA).



Effects of Spark Advance on Emissions and Driveability• Too much spark advance, particularly during high engine load conditions, increases the

likelihood of engine detonation and increases combustion temperature and pressure. This results in an increase in HC and NOx output, decreased engine performance, and possible permanent damage the engine.

• Too little spark advance causes only partial combustion of the air/ fuel charge, resulting in very poor engine performance and fuel economy. Partial combustion will also result in an increase in CO levels.

Functional TestingSpark advance problems can result from an incorrect initial timing setting or a problem with spark advance during operation. Before attempting to check spark advance during operating conditions, the initial or "base" ignition timing setting should checked and adjusted.

This procedure varies between systems, but on TCCS equipped vehicles, it generally requires jumping terminals at an underhood check connector (DLC1) to default the TCCS system to initial timing. After checking or adjusting initial timing, remove the test wire to inform the ECM to reestablish corrective control over timing. Refer to the Repair Manual for details on performing this procedure.



Even with initial timing correct, it is still possible that the system is miscalculating ignition timing as a result of incorrect sensor inputs. For example, if an airflow meter indicates light engine load, when in fact, the engine is experiencing high engine load, the ECM may incorrectly respond by over advancing ignition timing to the point of causing detonation. Refer to course 850 and 873 handbook for additional information on spark advance control strategy.

If inaccurate sensor inputs are suspected on earlier EFI and TCCS vehicles, it is recommended that you perform standard voltage checks of all major sensor inputs to the ECM. Compare these readings to those listed on the standard voltage chart on the Repair Manual or readings obtained from other known good vehicles. On OBD-II vehicles, you may observe ignition timing and identify incorrect signal data using the Diagnostic Tester. Some of the more important spark control parameters include engine speed, engine load, throttle angle, and coolant temperature.

On early EFI vehicles, all spark advance is handled by mechanical means. This system uses a centrifugal advance mechanism to represent engine speed and vacuum advance mechanism to represent engine load. Resolving advance problems with this type system requires inspecting governor weights, springs, pivots, signal rotor, vacuum diaphragm, vacuum signal source, breaker plate, etc.



Knock Detection ControlThe KNK (knock) input signal is critical in the prevention of engine detonation. The ECM uses the knock sensor(s) to determine when, and to what degree, engine detonation is occurring and then retards ignition timing as needed. The spark advance program is designed to provide the maximum spark advance possible, while keeping the engine from producing an audible "ping". If problems occur with this input signal, detonation may result, producing significant levels of HC and NOx emissions.

The ECM is designed to filter out KNK signal voltages that it considers are outside of the engine detonation range. Thus, a check of a knock control system by tapping on the engine close to the knock sensor may produce an output signal, but will not cause spark timing to retard. A check of the KNK signal pattern using the Diagnostic Tester Oscilloscope or lab scope may provide you the most diagnostic information.



Idle Air Control SystemsThe Idle Air Control (IAC) system is used to stabilize idle speed during cold engine and after warm-up operations. Idle speed stabilization is needed due to the effect engine load changes has on emission output, idle quality and vehicle driveability. The IAC system uses an ECM controlled idle air control valve (IACV) that regulates the volume of air bypassed around the closed throttle. The ECM controls the IACV by applying various input signals against an IAC program stored in memory.

There are four different types of IACVs used on Toyota models. These systems are referred to as:

• Step-Motor • Duty-Control Rotary Solenoid • Duty-Control Air Control Valve (ACV) • On/Off Vacuum Switching Valve (VSV)

Step-Motor IAC SystemThis system uses a step-motor type IACV to control bypass airflow. The IACV consists of a step-motor with four coils, magnetic rotor, valve and seat, and can vary bypass airflow by positioning it's valve into one of 125 possible "steps". Basically, the higher the IACV step number, the larger the airflow opening and the greater the volume of air bypassed around the closed throttle.

The ECM controls IACV positioning by sequentially energizing its four motor coils. For each coil that is pulsed, the IACVs magnetic rotor moves one step, which in turn changes the valve and seat positioning slightly. The ECM commands larger IACV position changes by repeating the sequential pulses to each of the four coils, until the desired position is reached. If the IACV is disconnected or inoperative, it will remain fixed at it's last position.

EMISSION SUB SYSTEMS - Idle Air Control Systems


Duty-Control Rotary Solenoid IAC SystemThis system uses a rotary solenoid IACV to perform idle speed stabilization. Bypass air control is accomplished by means of a movable rotary valve which blocks or exposes a bypass port based on command signals from the ECM. The IACV consists of two electrical coils, permanent magnet, valve, bypass port, and bi-metallic coil.

The ECM controls IACV positioning by applying a duty cycled signal to the two electrical coils in the IACV. By changing the duty ratio (on time versus off time), a change in magnetic field causes the valve to rotate. Basically, as duty ratio exceeds 50%, the valve opens the bypass passage and as duty ratio drops below 50%, the valve closes the passage. If the IACV is disconnect or inoperative, the valve will move to a default position and idle rpm will be around 1000 to 1200 rpm at operating temperature.

Duty-Control ACV SystemThis system regulates air bypass volume by using an ECM duty-cycle controlled Air Control Valve (ACV). The ACV uses an electric solenoid to control a normally closed air valve which blocks passage of air from the air cleaner to the intake manifold. Since the ACV is incapable of flowing high air volume, a separate mechanical air valve is used to perform cold fast-idle on



vehicles equipped with this system. With this type system, the ECM varies bypass airflow by changing the duty ratio of the command signal to the ACV. By increasing the duty ratio, the ECM holds the air bypass open longer, causing an increase to idle speed. The ACV does not have any effect on cold fast idle or warm-up fast idle speed, and is only used during starting and warm curb-idle.

On/Off VSV Type IAC SystemThis type of IAC system uses a normally closed Vacuum Switching Valve (VSV) to control a fixed air bleed into the intake manifold. This on/off type VSV is controlled by signals from the ECM or directly through the tail lamp or rear window defogger circuits.

The ECM controls the VSV by supplying current to the solenoid coil when preprogrammed conditions are met. Also, current can be supplied to the solenoid from the tail lamp or rear window defogger circuits by passing through isolation diodes. Engines using this IAC system must also use a mechanical air valve for cold fast-idle.

IAC System Control ParametersDepending on system type and application, the IAC system may perform a combination of the following control functions; initial set-up, engine startup, warm-up control, feedback idle control, engine speed estimate control, electric load idle-up, learned idle speed control, and A/T idle-up control. Refer to course 850 handbook for specific details concerning the operating parameters for each of the IAC systems.



Air ValvesThere are two types of non-ECM controlled air valves that are used on some engines to perform cold fast-idle control. The first type simply uses a thermo-wax element to vary the amount of bypass air based on the coolant temperature. Once the engine reaches operating temperature, the air valve should be fully closed.

The second type uses a spring loaded gate balanced against a bi-metal element. As engine temperature rises, the bi-metal element deflects to close the gate valve, thereby reducing the amount of bypass air. A heater coil surrounds the bi-metal element and is used to heat the element whenever the engine is running (fuel pump operates). An air valve quick check can be performed by pinching off the supply hose and observing rpm drop. The drop should be less than 50 rpm when the engine is warm, and should be significantly higher when the engine is cold.



Effects of IAC Operation on Emissions & DriveabilityImproper operation of the IAC system can have significant impact on idle quality and driveability. If idle speed is too low, the engine may stall or idle very rough. If idle speed is too high, harsh A/T gear engagement may result.

On some IAC systems, the IACV step count or ECM duty ratio may provide hints as to whether a major correction is being made to offset a idle speed problem. For instance, if false air entry causes idle speed to be much higher than normal, the IAC system may correct for this condition by decreasing bypass air volume in an effort to bring idle speed back to the "target" idle speed.

The IACV step count or duty ratio may also identify a restricted air passage, misadjusted throttle, or IAC valve problem. Observe IAC signal data at idle, while applying various "loads" to the engine. Look for a corresponding change to IACV step count or duty ratio, as loads are placed on the engine. Also, a signal comparison to other known good vehicles may be helpful.

IAC System Functional TestsBecause functional checks vary between the four major types of IAC systems, refer to the Repair Manual for specific procedures on performing an on-vehicle IAC inspection. On some late model OBD-II vehicles, an active test feature will allow you to manually command IACV positioning from fully open to fully closed. A quick check can be made by commanding a change to IACV positioning while watching for expected changes to idle rpm.



Exhaust Gas Recirculation SystemThe Exhaust Gas Recirculation (EGR) system is designed to reduce the amount of Oxides of Nitrogen (NOx) created by the engine during operating periods that usually result in high combustion temperatures. NOx is formed in high concentrations whenever combustion temperatures exceed about 2500’F.

The EGR system reduces NOx production by recirculating small amounts of exhaust gases into the intake manifold where it mixes with the incoming air/fuel charge. By diluting the air/fuel mixture under these conditions, peak combustion temperatures and pressures are reduced, resulting in an overall reduction of NOx output. Generally speaking, EGR flow should match the following operating conditions:

• High EGR flow is necessary during cruising and mid-range acceleration, when combustion temperatures are typically very high

• Low EGR flow is needed during low speed and light load conditions • No EGR flow should occur during conditions when EGR operation could adversely affect

engine operating efficiency or vehicle driveability (engine warm up, idle, wide open throttle, etc.)

EGR Impact on the Engine Control SystemThe ECM considers the EGR system an integral part of the entire Engine Control System (ECS). Therefore, the ECM is capable of neutralizing the negative performance aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods of high EGR flow. By integrating fuel and spark control with the EGR metering system, engine performance and fuel economy can actually be enhanced when the EGR system is functioning as designed.

EMISSION SUB SYSTEMS - Exhaust Gas Recirculation


EGR Theory of OperationThe purpose of the EGR system is to precisely regulate EGR flow under different operating conditions, and to override flow under conditions which would compromise good engine performance. The precise amount of exhaust gas which must be metered into the intake manifold varies significantly as engine load changes. This results in the EGR system operating on a very fine line between good NOx control and good engine performance.

If too much exhaust gas is metered, engine performance will suffer. If too little EGR flows, the engine may knock and will not meet strict emissions standards. The theoretical volume of recirculated exhaust gas is referred to as EGR ratio. As the accompanying graph shows, the EGR ratio increases as engine load increases.

EGR System ComponentsTo achieve this designed control of exhaust gas recirculation, the system uses the following components:

• Vacuum Actuated EGR Control Valve

• EGR Vacuum Modulator Assembly

• ECM Controlled Vacuum Switching Valve (VSV)

EGR Control ValveThe EGR control valve is used to regulate exhaust gas flow to the intake system by means of a pintle valve attached to the valve diaphragm. A ported vacuum signal and calibrated spring on one side of the diaphragm are balanced against atmospheric pressure acting on the other side of the diaphragm. As the vacuum signal applied to the valve increases, the valve is pulled further from ifs seat. The key to accurate EGR metering is the EGR vacuum modulator assembly which precisely controls the strength of the applied vacuum signal.



EGR Vacuum ModulatorBecause exhaust backpressure increases proportionally with engine load, the EGR vacuum modulator uses this principle to precisely control the strength of the vacuum signal to the EGR valve. The typical EGR control system uses two ported vacuum signals from the throttle body. Port E is the first stage ported vacuum signal and Port R is the second stage ported vacuum signal uncovered by the opening throttle valve.

When vacuum is applied from port E, the strength of the vacuum signal applied to the EGR valve will be dependent on the amount of exhaust backpressure acting on chamber A of the vacuum modulator. When vacuum is applied from port R, the strength of the vacuum signal applied to the EGR valve will no longer be dependent on the strength of the exhaust backpressure signal. During this mode, the EGR signal strength is determined solely by



the strength of the vacuum signal from port E of the throttle body. The EGR vacuum modulator provides the ability to precisely match EGR flow rate to amount of load applied to the engine.

ECM Controlled Vacuum Switching Valve (VSV)In addition to the EGR modulator, an ECM controlled VSV is used to inhibit EGR operation during conditions where it could adversely affect engine performance and vehicle driveability. The EGR VSV can be either normally open or closed and installed in series between the vacuum modulator and EGR valve or installed on a second port on the EGR valve. This VSV controls an atmospheric bleed which inhibits EGR operation any time a given set of ECM parameters are met.

ECM Override of EGRAs mentioned, the ECM is capable of inhibiting EGR flow through operation of the VSV bleed. When the ECM determines an inhibit condition, it de-energizes the VSV, blocking the vacuum signal to the EGR valve and opening the valve diaphragm to an atmospheric bleed. This causes the EGR valve to close. Typical EGR inhibit parameters are shown below.

Variations on EGR VSV PlacementThere are three basic variations of the EGR vacuum circuit depending on engine application. All three systems function similarly, the only difference being the placement of the VSV in the vacuum circuit and the logic of the VSV and ECM.



EGR Fault Detection SystemAn EGR malfunction detection system is incorporated into the TCCS system to warn the driver when the EGR system is not operating properly. The system uses an Exhaust Gas Temperature (THG) sensor on the intake side of the EGR valve where it is exposed to exhaust gas flow whenever the EGR valve opens.

The ECM compares the THG signal with parameters stored in memory. If EGR gas temperature is determined to be too cold when the ECM has the EGR valve enabled, the MIL will be illuminated, and a diagnostic code will be stored in ECM memory. This diagnostic configuration allows the ECM to monitor entire EGR system operation.

EGR Effect On Emissions & Driveability• Too little EGR flow may cause detonation and IM240 emissions failure for excessive NOx.

Because EGR tends to reduce the volatility of the air/fuel charge, loss of EGR typically causes detonation to occur. If EGR is commanded but doesn't flow (restricted passage in manifold, nonfunctional valve, etc.) severe detonation will occur.

• Too much EGR flow and/or excessive flow for driving conditions may cause stumble, flat spot, hesitation, and surging. Because EGR dilutes the air/fuel charge, too much EGR for a given engine demand can cause a misfire. It is not uncommon to see tip in hesitation, stumble and surging when too much EGR is metered.

EGR System Functional TestsOn some OBD-II vehicles, the EGR system can be controlled using the active test feature of the Diagnostic Tester. This is the easiest way to verify EGR system operation and can generally be performed as follows:

• Start the engine and allow it to reach operating temperature

• Using the Diagnostic Tester, access the Active Test menu

• Select "EGR System" from the Active Test menu

• Raise engine speed and maintain a steady 3000 rpm

• Activate the EGR VSV (turn EGR On)

• You should notice a slight drop in engine speed and a rise in EGRT gas temperature as EGR is activated

If engine speed and EGRT gas temperature does not change, the EGR system is not functioning and the problem may be mechanical or electrical. If the rpm drop is very slight, the problem may be a partially blocked or restricted EGR passage.



EGR System InspectionOn other vehicles, the only way to accurately check the operation of the EGR system is to perform a systematic inspection of the entire system. The following inspection procedures are for a 95 5S-FE Camry:

• First, inspect the EGR modulator filter and, if necessary, remove and clean the filter with compressed air.

• "Tee" a vacuum gauge into the vacuum line between the EGR valve and VSV. • Start the engine and confirm that it does not run rough at idle. Note: This verifies that the

EGR valve is closed. • Next, connect terminals TE1 to E1 at DLC 1.

• With coolant temperature cold (A/T: below 140' F, M/T: below 131' F) and engine at 2500 rpm, the vacuum gauge should indicate zero.

Note: This verifies that the VSV is inhibiting EGR flow during cold engine operations.



• Next, warm the engine to operating temperature and maintain 2500 rpm. The vacuum gauge should now indicate low vacuum (typically around 3")

Note: This verifies proper low vacuum signal to the EGR valve during light engine load conditions.

• Next, with engine speed at 2500 rpm, connect the R port of the EGR modulator directly to a manifold vacuum source. The vacuum gauge should now indicate high vacuum (typically around 13") and the engine should run rough.

Note: This verifies proper high signal vacuum to the EGR valve when R port vacuum overrides the backpressure modulator.

• Disconnect terminals TE1 and El at DLC1 and reattach the EGR hoses to their original location.



If the problem is related to the EGR valve itself, make sure heavy carbon deposits are not keeping the valve unseated or causing it to stick when opening. Also, if EGR valve control is OK remove the valve and check the EGR exhaust and intake passages for restrictions. Heavy carbon deposits can be removed by using a special carbon scrapping tool.

This inspection example systematically confirms the integrity of the EGR valve, VSV, backpressure modulator, system hoses, and EGR passages. Once the suspect part/component is identified, it should be individually tested and then repaired or replaced as necessary. Because slight model to model variations exist between EGR systems, refer to the Repair Manual for specific EGR system inspection procedures.



Evaporative Emission Control SystemApproximately 20% of all hydrocarbon (HC) emissions from the automobile originate from evaporative sources. The Evaporative Emission Control (EVAP) system is designed to store and dispose of fuel vapors normally created in the fuel system; thereby, preventing its escape to the atmosphere. The EVAP system delivers these vapors to the intake manifold to be burned with the normal air/fuel mixture. This fuel charge is added during periods of closed loop operation when the additional enrichment can be managed by the closed loop fuel control system. Improper operation of the EVAP system may cause rich driveability problems, as well as failure of the Two Speed Idle test or Enhanced I/M evaporative pressure or purge test.

The EVAP system is a fully closed system designed to maintain stable fuel tank pressures without allowing fuel vapors to escape to the atmosphere. Fuel vapor is normally created in the fuel tank as a result of evaporation. It is then transferred to the EVAP system charcoal canister when tank vapor pressures become excessive. When operating conditions can tolerate additional enrichment, these stored fuel vapors are purged into the intake manifold and added to the incoming air/fuel mixture.

EMISSION SUB SYSTEMS - Evaporative Emission Control System


Toyota vehicles use two different types of evaporative emission control systems:

• Non-ECM controlled EVAP systems use solely mechanical means to collect and purge stored fuel vapors. Typically, these systems use a ported vacuum purge port and a Thermo Vacuum Valve (TVV) to prohibit cold engine operation.

• ECM controlled EVAP systems uses a manifold vacuum purge source in conjunction with a duty cycled Vacuum Switching Valve (VSV). This type of EVAP system has the ability to provide more precise control of purge flow volume and inhibit operation.

Non-ECM Controlled EVAP SystemNon-ECM controlled EVAP systems typically use the following components:

• Fuel tank

• Fuel tank cap (with vacuum check valve)

• Charcoal canister (with vacuum & pressure check valves)

• Thermo Vacuum Valve (TVV)

• Ported vacuum purge port (port P; on throttle body)

EVAP System OperationUnder some conditions, the fuel tank operates under a slight pressure to reduce the possibility of pump cavitation due to fuel vaporization. Pressure is created by unused fuel returning to the tank and is maintained by check valve #2 in the charcoal canister and the check valve in the fuel tank cap.

Under other conditions, as fuel is drawn from the tank, a vacuum can be created in the tank causing it to collapse. This is prevented by allowing atmospheric pressure to enter the tank through check valve #3 in the charcoal canister or the fuel tank cap check valve. The EVAP system is designed to limit maximum vacuum and pressure in the fuel tank in this manner.

When the engine is running, stored fuel vapors are purged from the canister whenever the throttle has opened past the purge port (port P) and coolant temperature is above a certain point (usually around 129' F). Fuel vapors flow from the high pressure area in the canister, past check valve #1 in the canister, through the Thermo Vacuum Valve (TVV), to the low pressure area in the throttle body. Atmospheric pressure is allowed into the canister through a filter located on the bottom of the canister. This ensures that purge flow is constantly maintained whenever purge vacuum is applied to the canister.

When coolant temperature falls below a certain point (usually around 95’F), the TVV prevents purge from taking place by blocking the vacuum signal to check valve #1.



ECM Controlled EVAP System OperationIntroduced on the'95 Avalon for CA, this system is similar to the Non-ECM controlled systems, except that an ECM controlled Vacuum Switching Valve (VSV) is used in place of the Thermo Vacuum Valve (TVV). The VSV is normally closed and duty cycle controlled, which means the ECM rapidly opens and closes the VSV passage to provide precise, variable control of purge flow volume and inhibit operation.

Because this system uses a manifold vacuum purge port, it may provide slight purge flow during idle if conditions can tolerate its enrichment. The ECM uses engine speed, intake air volume, coolant temperature, and oxygen sensor information to control EVAP operation.

EVAP Purge System MonitoringBy monitoring the oxygen sensor and injection pulse width as the canister is being purged, the ECM can detect the reduction of exhaust oxygen content and corresponding decrease in injection pulse width to correct for this momentary rich condition. In this manner, the ECM can detect a failure in the EVAP purge control system and store a DTC to alert the vehicle operator of the malfunction. Purge flow monitoring is only used on '95 and later OBD-II equipped vehicles.

EVAP Effect on Emissions and DriveabilityDuring Two Speed Idle tests, it is not uncommon for vehicles to fail off idle tailpipe tests for excessive CO emissions due to normal evaporative purge cycle operation. It is also possible for the charcoal canister to become saturated with liquid fuel to the degree that it becomes unserviceable.



To avoid emissions failures due to normal evaporative emissions purge cycle, the vehicle should not be tested after long hot soak periods, prolonged idle or after having been left in sitting in the sun on a hot day. All of these conditions will cause large amounts of fuel vapor to store in the charcoal canister. To put the EVAP system through it's normal purge cycle, the vehicle can be driven at highway speeds for five minutes. This should purge any vapor from the canister which would normally accumulate during the above mentioned conditions.

If the canister continues to cause high CO emissions after a normal purge cycle has been performed, it is possible that the canister is irrecoverably saturated. If the EVAP is suspected as potential cause of high CO emissions failure or rich driveability problems, the following checks should be made:

• Isolate the EVAP system from the engine intake by removing the purge port hose from throttle body port.

• Test vehicle with EVAP system isolated.

If the EVAP system is determined to be at fault, use procedures in the appropriate Repair Manual to inspect the charcoal canister, filter, check valves, TVV or VSV and the related vacuum plumbing.



Enhanced I/M EVAP Purge and Pressure Test Diagnosis Evaporative System Purge and Pressure Tests will be required as a part of Enhanced I/M testing. If the vehicle fails for either purge or pressure, checks can be made to verify the operation and integrity of evaporative control system.

EVAP System Pressure Test DiagnosisThe Enhanced I/M Evaporative Pressure Test is performed by filling the EVAP vapor line and fuel tank with nitrogen to a pressure of 14 inches of water (approximately 0.5 psi). If the system maintains at least 8 inches of water pressure after 2 minutes, it passes the test.

If the EVAP system fails the pressure test, a leak exists either in the vapor vent line between the canister and tank, the fuel tank itself, or the fuel cap. Visual checks may or may not identify the source of leak(s) in the system; however, you should never pressurize the EVAP system with shop air! Doing this would introduce oxygen into the EVAP system were it could combine with fuel vapors and create a very explosive condition. Secondly, the system is tested at very low pressure which would make accurate, pressure regulation difficult. If the system was accidentally pressurized beyond this point, severe damage to the system may result.



EVAP Pressure Testing Using Special Test EquipmentThe best way to test and identify leak(s) that cause a pressure test failure is to use special EVAP pressure testing equipment available from aftermarket suppliers. This equipment allows you to perform an actual pressure test, in addition to having features that help you locate the leak. There are many variations and differences between test equipment and procedures, but for the sake of example, here is the test procedure for an EVAP pressure tester that uses pressurized nitrogen gas:

1. Disconnect the fuel tank vapor line from the canister and attach the pressure tester to this line.

Note: The tester may have an adapter that allows you to connect the pressure line between the tank filler neck and the fuel cap.

2. Activate the tester and pressurize the line until 14 inches of water pressure is maintained.

3. Observe the pressure gauge and note if the pressure begins to drop.

Note: It is normal for pressure to initially rise or fall slightly then stabilize after a few seconds. This is caused by the initial temperature variation between the nitrogen and EVAP fuel vapors. Once temperatures stabilize, the pressure will equalize if no leak exist.

4. If the pressure drops dramatically, listen for leaks from the fuel cap, tank seams, and hoses.

5. Check for frayed or cracked hoses, poor connections, damaged fuel tank seams, faulty fuel cap gasket or check valve.

6. The leak may be found by spraying the suspected area with soapy water and looking for bubbles.

7. Special ultrasonic leak detectors are now available that can "listen" for the exact frequencies caused by these low pressure leaks. Another method uses the exhaust analyzer to check for the escape of fuel vapors (HC) from the leaky part/component.

Note: The drawback to using the exhaust analyzer is the limited amount of fuel vapors that exist in EVAP system (fuel tank). If the leak is not quickly identified, all HC vapors will escape leaving only a nitrogen (inert gas) leak to locate.

8. If the leak cannot be identified by the completion of the test, select the manual mode that provides a constant pressure on the system.

9. Once the leaky part/component is identified, perform the needed repair or replacement.



EVAP Purge Test DiagnosisThe evaporative purge test is performed during the IM240 transient (drive cycle) test. A flow transducer is placed in series with the purge line between the canister and engine. In order to pass, the system must purge at least 1 liter of flow by the end of the IM240 drive cycle. Toyota vehicles with properly operating EVAP systems normally purge 25 liters or more by the completion of drive cycle.

If the EVAP system fails the purge test, a problem exists with the purge port, the purge hose to the canister, or the charcoal canister itself. Since 1 liter of flow is such a nominal amount, the test really only verifies whether the system is purging or not. There are checks that you can make to confirm vacuum to the canister or the effects of purge flow on the air/fuel mixture; however, the only real way of measure actual flow volume is to use a flow transducer, similar to the one used in the actual purge test.

EVAP Purge Test Using Special EquipmentThe most accurate method of checking EVAP purge flow is to check the system in the same manner in which it was tested. EVAP purge flow testers (sometimes combined with pressure testers) are currently available from aftermarket sources and typically operates as follows:

1. Precondition the vehicle by running the engine until it reaches operating temperature.

2. Connect the tester's flow transducer into the EVAP purge line between the engine and evaporative canister.

3. With the engine off, zero the tester to calibrate the purge flow reading.

4. Next, with the engine idling, start the timer and observe the purge flow rate and accumulated purge volume on the tester display.



Note: On TVV equipped systems that use a ported vacuum purge source, no purge should take place during idle, however, on systems using a VSV, the ECM may command a very slight amount of flow during idle.

5. Slowly raise engine speed and maintain a steady 2500 rpm. During this period purge flow should increase dramatically and, on a properly functioning EVAP system, 1 liter of flow should be surpassed in a matter of seconds.

6. If the system does not flow at least 1 liter within the 240 second test period or it marginally passes the test, perform the following functional checks to help identify the suspect parts or components.

Note: Since most vehicles flow 25 liters or more during the same period, marginal passes should also be checked and repaired since these systems are not functioning properly and will probably fail in future tests.

7. Once the problem has been identified and repaired, perform this test again to confirm sufficient improvements in purge volume.



EVAP System CheckIf the system fails the purge flow test or flows very little, the following Evaporative Emission System Check may help identify problems causing no or low purge flow. The following inspection procedures are for a '95 5S-FE Camry:

1. First, visually inspect the fuel tank, fuel cap, canister, lines and connections for any damage, cracks, fuel leakage, or deterioration and repair or replace as necessary.

2. Check the canister for a clogged filter or stuck check valve by performing the following:

• Apply low pressure compressed air (0.68 psi) into the fuel tank vapor port (port A) of the canister and confirm that air flows out from all other canister ports.

Note: Airflow from canister ports is difficult to detect.

• Next, apply low pressure compressed air to the purge port (port B) of the canister and confirm that air does not flow out from any of the other ports.

Note: Replace the canister if a problem is detected with either of the checks above.

• Clean the canister filter by applying air pressure (43 psi) to the tank vapor port (port A) while holding the purge port (port B) closed with your finger.

Note: If carbon blows out during this test replace the canister.



3. Check the operation of the TVV by performing the following:

• Disconnect the hoses from the TVV and then attach a hand operated vacuum pump to the lower port of the TVV.

• With coolant temperature cold (below 95’F), operate the vacuum pump and confirm that air does not flow (vacuum is held) from the upper port to the lower port.

Note: It is normal for some TVWs to allow a slight amount of airflow when cold.

• Next, allow coolant temperature to rise above 129' F. Operate the vacuum pump and confirm that air now flows (vacuum bleeds off) between the top port and the lower port.

Note: If the TVV fails any of the checks above, replace it.

This EVAP check example systematically confirms the integrity of the evaporative canister and TVV. Once repair or replacement is made, retest the system to confirm sufficient purge improvement needed to pass a retest. Because slight variations exist between evaporative system tests, refer to the Repair Manual for specific EVAP test procedures and specifications.



Positive Crankcase Ventilation System During normal compression stroke, a small amount of gases in the combustion chamber escapes past the piston. Approximately 70% of these "blowby" gases are unburned fuel (HC) that can dilute and contaminate the engine oil, cause corrosion to critical parts, and contribute to sludge build up. At higher engine speeds, blowby gases increase crankcase pressure that can cause oil leakage from sealed engine surfaces.

The purpose of the Positive Crankcase Ventilation (PCV) system is to remove these harmful gases from the crankcase before damage occurs and combine them with the engine's normal incoming air/fuel charge. Fuel injected Toyota vehicles use two different types of closed PCV systems to prevent the escape of crankcase vapors into the atmosphere:

• Fixed Orifice PCV System

• PCV System Using Variable Flow PCV Valve

Fixed Orifice PCV SystemOn some early Toyota EFI vehicles, a fixed orifice PCV system is used to meter blowby from the crankcase into the intake manifold, where they would be consumed during normal engine operation. This system is simple in design and construction, and provides crankcase ventilation based on the size of the fixed orifice valves and the normal operating characteristics of intake manifold vacuum. The two fixed orifice valves are used to balance the strength of vacuum applied to the crankcase as engine operating conditions change. The biggest drawback of this type system is that blowby production does not always match intake manifold vacuum characteristics.

EMISSION SUB SYSTEMS - Positive Crankcase Ventilation System


PCV System Using Variable-Flow PCV ValveUnlike fixed orifice type systems, PCV systems that use a variable-flow PCV valve more accurately match ventilation flow with blowby production characteristics. By accurately matching theses two factors, crankcase ventilation performance is optimized, while engine performance and driveability remains unaffected.



PCV System Components The variable-flow type PCV systems are also very simple in design and consists of the following components:

• PCV Valve

• PCV purge hose

• Breather hose

PCV System OperationLike the previous system, this system also uses manifold vacuum to draw crankcase vapors back into the intake manifold. Typically, blowby production is the greatest during high load operations and very light during idle and light load operations. Since the characteristics of manifold vacuum do not match the flow requirements needed for proper crankcase ventilation, a PCV valve is used to regulate blowby flow back into the intake manifold.

• During idle and deceleration, blowby production is very low, but intake manifold vacuum is very high. This causes the pintle inside the PCV valve to fully retract against spring tension. The positioning of the pintle provides a small vacuum passage and allows for low blowby flow to the combustion chamber.

• During low load cruising, the pintle inside the PCV valve is positioned somewhat in the center of its travel. This positioning allows a moderate volume of blowby flow into the combustion chamber.



• During acceleration and high load operations, blowby production is very high. The pintle extends out further from the restriction allowing the maximum flow of blowby into the combustion chamber. During extremely high engine loads, if blowby volume exceeds the ability of the PCV valve to draw in the vapors, the excess blowby flows through the breather hose to the air cleaner housing where it can enter the combustion chamber.

• When the engine is off or it backfires, spring tension closes the valve completely preventing the release of blowby into the intake manifold. The valve closes during a backfire to prevent the flame from traveling into the crankcase where it could ignite the enclosed fuel vapors.

PCV System Effects on Emissions and DriveabilityBecause PCV operation is factored into the proper operation of the feedback control system, problems with the PCV system may disrupt the normal air/ fuel ratio balance. A plugged PCV valve will prevent the normal flow of crankcase vapors into the engine and can result in a richer than normal air/fuel mixture. A plugged crankcase breather hose may cause the engine to consume oil because of the increased level of crankcase vacuum.

In addition, depending on the location of the fresh air breather hose, a nonfunctional valve or restricted vacuum hose can cause oil contamination in the air cleaner housing or throttle bore coking. Always suspect and check the PCV system if you find traces of oil in the air intake system.



If the crankcase becomes diluted with fuel, carbon monoxide (CO) levels will likely increase because the PCV system will meter extra fuel vapor into the intake system. Always replace fuel diluted engine oil and identify and resolve the problem causing the fuel contaminated.

Although there are no mandatory maintenance intervals for the PCV system, periodically check the system for a plugged or gummed PCV valve and damaged hoses. Replace suspect components as necessary. Since PCV flow rates differ between vehicle models, it is important to use the correct replacement PCV valve to ensure proper operation. The installation of an incorrect valve may cause engine stalling, rough idle and other driveability complaints. Thus, never install universal type PCV valves!

PCV System Functional TestsThe following RPM Drop Test may be used as a basic quick check to confirm that the PCV system is functioning:

• Start the engine and allow it to reach operating temperature

• On TCCS equipped vehicles, connect TE to E1 at the diagnostic connector

• Allow the engine to stabilize at idle

• Pinch or block the hose between the PCV valve and vacuum source

• Typically, engine rpm should drop around 50 rpm If engine rpm does not change, check the PCV valve and system hoses for blockage. Replace components as necessary and then retest the system.



Catalytic ConverterRegardless of how perfect the engine is operating, there will always be some harmful by-products of combustion. This is what necessitates the use of a Three-Way Catalytic (TWC) Converter. This device is located in-line with the exhaust system and is used to cause a desirable chemical reaction to take place in the exhaust flow.

Essentially, the catalytic converter is used to complete the oxidation process for hydrocarbon (HC) and carbon monoxide (CO), in addition to reducing oxides of nitrogen (NOx) back to simple nitrogen and carbon dioxide.

TWC ConstructionTwo different types of Three-Way Catalytic Converters have been used on fuel injected Toyota vehicles. Some early EFI vehicles used a pelletized TWC that was constructed of catalyst coated pellets tightly packed in a sealed shell, while later model vehicles are equipped with a monolith type TWC that uses a honeycomb shaped catalyst element. While both types operate similarly, the monolith design creates less exhaust backpressure, while providing ample surface area to efficiently convert feed gases.

EMISSION SUB SYSTEMS - Catalytic Converter


The Three-Way Catalyst, which is responsible for performing the actual feed gas conversion, is created by coating the internal converter substrate with the following key materials:

• Platinum/Palladium; Oxidizing catalysts for HC and CO

• Rhodium; Reducing catalyst for NOx

• Cerium; Promotes oxygen storage to improve oxidation efficiency The diagram below shows the chemical reaction that takes place inside the converter.

TWC OperationAs engine exhaust gases flow through the converter passageways, they contact the coated surface which initiate the catalytic process. As exhaust and catalyst temperatures rise, the following reaction occurs:

• Oxides of nitrogen ( NOx) are reduced into simple nitrogen (N2) and carbon dioxide (CO2)

• Hydrocarbons (HC) and carbon monoxide (CO) are oxidized to create water (H2O) and carbon dioxide (CO2)



Catalyst operating efficiency is greatly affected by two factors; operating temperature and feed gas composition. The catalyst begins to operate at around 550' F.; however, efficient purification does not take place until the catalyst reaches at least 750' F. Also, the converter feed gasses (engine-out exhaust gases) must alternate rapidly between high CO content, to reduce NOx emissions, and high O2 content, to oxidize HC and CO emissions.

Effects of Closed Loop Control on TWC OperationTo ensure that the catalytic converter has the feed gas composition it needs, the closed loop control system is designed to rapidly alternate the air/fuel ratio slightly rich, then slightly lean of stoichiometry. By doing this, the carbon monoxide and oxygen content of the exhaust gas also alternates with the air/fuel ratio. In short, the converter works as follows:

• When the A/F ratio is leaner than stoichiometry, the oxygen content of the exhaust stream rises and the carbon monoxide content falls. This provides a high efficiency operating environment for the oxidizing catalysts (platinum and palladium). During this lean cycle, the catalyst (by using cerium) also stores excess oxygen which will be released to promote better oxidation during the rich cycle.

• When the A/F ratio is richer than stoichiometry, the carbon monoxide content of the exhaust rises and the oxygen content falls. This provides a high efficiency operating environment for the reducing catalyst (rhodium). The oxidizing catalyst maintains its efficiency as stored oxygen is released.



As mentioned in the beginning of this section, precise closed loop control relies on accurate feedback information provided from the exhaust oxygen sensor. The sensor acts like a switch as the air/fuel ratio passes through stoichiometry.

Closed loop fuel control effectively satisfies the three way catalyst's requirement for ample supplies of both carbon monoxide and oxygen. Generally speaking, if the closed loop control system is functioning normally, and fuel trim is relatively neutral, you can be assured that the air induction and fuel delivery sub-systems are also operating normally. If the closed loop control system is not working properly, the impact on catalytic converter efficiency, and ultimately emissions, can be significant.



Effects of Oxygen Sensor DegradationSince the oxygen sensor is the heart of the closed loop control system, proper operation is critical to efficient emission control. There are several factors which can cause the oxygen sensor signal to degrade and they include the following:

• Silicon contamination from chemical additives, some RTV sealers, and contaminated fuel.

• Lead contamination can be found in certain additives and leaded motor fuels.

• Carbon contamination is caused by excessive short trip driving and/or malfunctions resulting in an excessively rich mixture.

The effects of sensor degradation can range from a subtle shift in air/fuel ratio to a totally inoperative closed loop system. With respect to driveability and emissions diagnosis, a silicon contaminated sensor will cause the most trouble.

When silicon burns in the combustion chamber, it causes a silicon dioxide glaze to form on the oxygen sensor. This glaze causes the sensor to become sluggish when switching from rich to lean, and in some cases, increases the sensor minimum voltage on the lean switch. This causes the fuel system to spend excessive time delivering a lean mixture.



It is often difficult to identify a sensor which is marginally degraded, and in many cases, vehicle driveability may not be effected significantly. With the advent of IM240 emissions testing, however, marginal sensor degradation may cause some vehicles to fail the NOx portion of the loaded mode test.

The impact of a slightly lean mixture has a dual effect on emissions. A leaner mixture means higher combustion temperatures so more NOx is produced during combustion. Additionally, because less carbon monoxide is available in catalyst feed gas, the reducing catalyst efficiency falls off dramatically. The end result is a vehicle which may fail an IM240 test for excessive NOx.



As previously mentioned, the O2S signal voltage must fluctuate above and below 0.45 volts at least 8 times in 10 seconds at 2500 rpm with the engine at operating temperature. During the rich swing, voltage should exceed 550 mv and during the lean swing should fall below 400 mv. O2S signal checks can be made using the Autoprobe feature of the Diagnostic Tester, digital multimeter, or 02S/RPM check using the Diagnostic Tester. Refer back to the oxygen sensor tests in the closed loop control section for specific test procedures.

Effects of TWC DegradationNow that we understand the effects of O2S degradation on catalyst efficiency, let's look at the effects of a catalytic converter failure. Keep in mind, there are many different factors that can cause its demise.

• Poor engine performance as a result of a restricted converter. Symptoms of a restricted converter include; loss of power at higher engine speeds, hard to start, poor acceleration and fuel economy.

• A red hot converter indicates exposure to raw fuel causing the substrate to overheat. This symptom is usually caused by an excessive rich air/fuel mixture or engine misfire. If the problem is not corrected, the substrate may melt, resulting in a restricted converter.

• Rotten egg odor results from excessive hydrogen sulfide production and is typically caused by high fuel sulfur content or air/fuel mixture imbalance. If the problem is severe and not corrected, converter meltdown and/or restriction may result.

• IM emission test failure may occur if catalyst performance falls below its designed efficiency level. Perform additional tests to confirm that the problem is in fact converter efficiency and not the result of engine or emission sub-system failure. Never use an emission test failure as the only factor in replacing a catalytic converter! If you do, you may not be fixing the actual cause of the emission failure.

Causes of TWC Contamination Like the oxygen sensor, the most common cause of catalytic converter failure is contamination. Examples of converter contaminants include:

• Overly rich air/fuel mixtures will cause the converter to overheat causing substrate meltdown.

• Leaded fuels, even as little as one tank full, may coat the catalyst element and render the converter useless.

• Silicone from sealants (RTV, etc.) or engine coolant that has leaked into the exhaust, may also coat the catalyst and render it useless.

There are other external factors that can cause the converter to degrade and require replacement. Thermal shock occurs when a hot converter is quickly exposed to cold temperature (snow, cold fuel, etc.), causing it to physically distort and eventually disintegrate. Converters that have sustained physical damage (seam cracks, shell puncture, etc.) should also be replaced as necessary.



TWC Functional ChecksBefore a converter is condemned and replaced, it is crucial that any problem(s) that may have contributed to the damage and failure of the converter is identified and repaired. If not, the replacement converter will soon fail!

Also, in order to accurately check catalytic converters, all engine mechanical, engine control systems, and emission sub-systems must be in proper working order or your results will be inaccurate. Remember, the converter relies on a narrow feed gas margin or efficiency suffers.

There are a number of tests that can be performed on catalytic converters; however, no one test should be used to verify the complete integrity and conversion efficiency of the converter. The following are examples of typical TWC checks.

Visual InspectionThe first check, and the easiest, is to perform a thorough visual inspection of the converter and related hardware. Many converter problems have obvious symptoms that are easily identified during a visual inspection. Look for the following; pinched exhaust pipe, physical damage to the insulator or converter shell, cracked or broken seams, excessive rust damage, mud or ice in the tailpipe, etc.

Rattle TestPerform a rattle test by firmly hitting the converter shell with the center of your palm (avoid hitting it too hard or you may damage it!) If the substrate is OK it should sound solid. If it rattles, the substrate has disintegrated and the converter should be replaced.



Restricted Exhaust System CheckDriveability comments like "lacks power under load" or "difficult to start, acts flooded and also lacks power" may indicate a restricted exhaust. In extreme cases the exhaust may be so restrictive that the engine will not start. Generally speaking, here's how to test for a restricted exhaust system:

• Attach a vacuum gauge to an intake manifold vacuum source.

• Allow the engine to reach operating temperature.

• From idle, raise engine speed to approximately 2000 rpm.

• Note: The vacuum reading should be close to normal idle reading.

• Next, quickly release the throttle.

Note: The vacuum reading should momentarily rise then smoothly drop back to a normal idle reading. If the vacuum rises slowly or does not quickly return to normal level, the exhaust system may be restricted.

If the catalyst has disintegrated, it is likely that contamination has also restricted the muffler. Don't overlook that possibility. If the engine will not start, try disconnecting the exhaust system at the manifold and see if the engine will start.

Lead Contamination CheckA common cause of converter contamination is lead poisoning. As mentioned, lead reduces converter efficiency by coating the catalyst element. Special lead detecting test paper (or paste) is available from aftermarket suppliers that checks for the presence of lead in the tailpipe. Follow the specific instructions provided by the test paper manufacturer.



TWC Efficiency Quick Check (CA Vehicles)On CA vehicles equipped with sub-O2 sensors, a quick check of TWC operation can be made by comparing the signal activity of the main oxygen sensor with the sub-oxygen sensor. Since the main O2S in located upstream of the converter and the sub-O2S is located downstream, a signal comparison would indicate whether a catalytic reaction is taking place inside the converter. If the catalyst is operating, the main O2S signal should normally toggle rich/lean, while the sub-O2 sensor should react very slowly (similar to a bad main O2S signal.) Main and sub O2S signals can be observed using the graphing display of the Diagnostic Tester (OBD-II) or V-BoB on other models.

NOTE: Before any catalyst efficiency tests are performed, it is important that both the engine and converter are properly preconditioned. Remember, proper feed gas conversion cannot take place until the closed loop control system is actively maintaining ideal mixture and the catalyst has reached operating temperature. To ensure these conditions are met, particularly during cold ambient conditions, operate the engine off-idle until the TWC is sufficiently heated. This will ensure optimal catalyst conversion efficiency.



Secondary Air Injection

Pulsed Secondary Air Injection System (PAIR)Combustion gases that enter the exhaust manifold are not completely burned and would continue to bum if not limited by the amount of oxygen in the exhaust system. To decrease the level of emissions emitted from the tailpipe, the Pulsed Secondary Air Injection (or Air Suction) system is used to introduce air into the exhaust flow, thereby allowing combustion to continue well into the exhaust system. This prolonged combustion (oxidation) period helps to lower the levels of HC and CO emissions that are forwarded to the catalytic converter. Additional air in the exhaust system also ensures that an adequate supply of oxygen is provided to the converter for catalyst oxidation.

Pulsed Secondary Air Injection (PAIR) systems do not use an air pump, but rely solely on the pressure differential that exists between atmospheric pressure and exhaust vacuum pulsation to draw air into the exhaust manifold.

System ComponentsToyota PAIR system uses the following components:

• PAIR valve (with reed valves)• Vacuum Switching Valve (VSV)• Check valve• Resonator• Air passage hoses

EMISSION SUB SYSTEMS - Secondary Air Injection


PAIR System OperationExhaust pressure is high when the exhaust valve opens to allow combustion gases into the exhaust manifold. However, once the valve closes, exhaust pressure drops below atmospheric pressure to create a vacuum in the exhaust manifold. This explains why exhaust pressure rapidly pulsates above and below atmospheric pressure.

The PAIR system promotes HC and CO oxidation by adding additional oxygen into the exhaust manifold during cold engine operation and deceleration (when very specific parameters are met). These operating conditions typically produce higher levels of HC and CO emissions.

This system simply provides a controlled air passage between atmosphere and the exhaust manifold. Whenever exhaust manifold pressure drops below atmospheric pressure, fresh air from the high pressure zone (atmosphere) flows through the system and enters the exhaust manifold where it promotes emission oxidation.

PAIR ValveThe PAIR system should only operate when needed; thus, a PAIR valve is used to control system air flow. It is simply a vacuum control diaphragm valve, similar to an EGR valve, that is opened to allow secondary air flow and closed to prohibit flow. The PAIR valve assembly also contains reed valves that prevent exhaust gases from entering system and possibly damaging it, when exhaust pressure exceeds atmospheric pressure.



ECM Controlled VSVAn ECM controlled VSV is located in-line with the vacuum signal to the PAIR valve. It is a normally closed VSV that is switched on by the ECM during conditions when emission production is high and fresh air is needed to promote emission oxidation. A resonator is located at the air intake and is used to baffle air pulsation that normally occurs during system operation.

PAIR System Operating StrategyPAIR operating strategy varies between different engine applications; therefore, refer to the Repair Manual for exact system operating parameters. An example of a typical program strategy (Truck with 22R-E engine) allows secondary air flow during the following conditions:

• Cold engine operation; when coolant temperature is below 86' F and engine speed is below 3600 rpm

• Deceleration; when either of the following conditions are met: -coolant temperature above 140’F, IDL on, and vehicle speed above 2 mph -coolant temperature above 140'F, IDL on, vehicle speed below 2 mph, and engine speed above 2,500 rpm

Effects of PAIR System on Emissions and Driveability In most cases, an inoperative PAIR system will have little effect on vehicle driveability; however, higher levels of emissions may result during periods when secondary air should be supplied (cold engine operation and deceleration). This is due to the lack of oxygen needed to prolong combustion in the exhaust manifold and assist the in catalyst oxidation.

PAIR System TestsA visual check of the PAIR system hoses and components may quickly identify problems that prevent secondary air flow. Check the air control and passage hoses for leaks, kinks, cracks, or damage and replace as necessary. Exhaust residue in the air induction system would indicate damaged reed valves. A functional check of the PAIR system can be performed as follows:

• Disconnect the PAIR system air intake hose from the air cleaner• Start the engine cold and allow it to idle. Confirm that a pulsating noise is heard from the

PAIR air intake hoseNote: This confirms secondary air flow during cold engine idle



• Allow the engine to reach operating temp. and let it idle. Confirm that no pulsating noise is heard from the PAIR air intake hose

Note: This confirms no secondary air flow during hot engine idle

• Next, race the engine and then snap the throttle closed. Confirm that a pulsating noise is initially heard from the PAIR air intake hose, then stops after a few seconds.

Note: This confirms secondary air flow during deceleration until engine speed falls below a certain level.

