automotive wave forms
DESCRIPTION
1TRANSCRIPT
Automotive Wave forms
Oscilloscope's
An oscilloscope can be a priceless price of test equipment used for observation of electrical/electronic wave patterns.
Oscilloscope's To properly use an oscilloscope you must
understand the scale selections. Must automotive oscilloscope will automatically
adjust to the proper scale. It’s the technician job to interpret the reading and
determine if the wave form is normal or defective. Not all devices operate in the same manner
please check manufactures specifications before replacing any sensor.
Oscilloscope's
Oscilloscope are used to measure voltage over a period of time.
An event that happens over a period of time is called frequency and in measured in Hertz per second.
1 Second Scale
TIME
VOLTAGE
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0
5
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15
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A
G
E
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10 1 Second scale
12.2 filter DC voltage
6 – 9 volts unfiltered DC voltage
4 Volts Peak to Peak AC Voltage
Grid lines
Oscilloscope's
Filtered voltage: A smooth supply of voltage.
Unfiltered voltage: Normally a ripple type wave pattern.
Oscilloscope's
An AC wave form change direction from positive to negative.
Peak voltage: is the voltage from the highest positive voltage to the lowest negative voltage reading.
+5
0
-5
Peak to Peak voltage is determine by multiplying:
Grid division x voltage setting = Peak to peak voltage
Oscilloscope's
Oscilloscope can be used to measure an event over a period of time. Frequency: Number of complete cycles per
second measured in hertz (Hz). Hertz (Hz): Unit of measurement for frequency. 1
hertz equal 1 cycle per second.
Oscilloscope's
To check frequency you may need some math.
Number of grid lines covered for 1 cycle divided by the time scale.
Wheel speed sensor
The Anti-lock Braking System (ABS) relies upon information coming in from speed sensors.
The wave form produced is used by the ABS control module to determine if wheel lock-up is occurring.
Two ABS wave forms. Both are good the difference is the meter set-up
2
VOLT
SCALE
5 mS Time Scale
NORAM ABS PATTERN
10 mS Time Scale Normal ABS Pattern
2VOLT
SCALE
10 mS2 Volts
Throttle Position Sensor A throttle position is
normally produces an analog signal.
The throttle position is normally used to tell the PCM the position of the throttle
Analog signal: an electrical signal that varies in strength.
200 mS Time Division
543210
Normal Throttle Position Wave Form
Most throttle position can be easily seen on the 200 mS scale
Throttle Held open Throttle Snapped
200 mS Time Division
543210
Normal Throttle Position Wave Form
Most throttle position can be easily seen on the 200 mS scale
Defective TPS
Air Flow Meters
The voltage output from the internal track of an Air Flow Meter (AFM) should be linear to flap movement,
This can be measured on an oscilloscope
MASS AIR FLOW METER
The waveform should show approximately 1.0 volt when the engine is at idle,
Voltage will rise as engine when engine speed is increased.
A peak voltage of around 4.5 is normal due to natural inertia.
Voltage will drop and then level off
Spike due to acceleration
Normal fall-off caused by inertia
Normal float back to match air flow
Throttle Released
Around 1 Volt at idle
Hot Wire Air flow Meters
5
4
3
2
1
0At idle around 1 volt normal
Voltage spike due to quick throttle opening
Cold air cooling of wire
Temperature stabilizes
Throttle Released
250 mS time division
5
4
3
2
1
0
A defective Mass Air Flow will have low voltage or operate erratic at all throttle angles.
A mass air flow angle should change in relation to throttle angle.
250 mS time division
Wave Forms Another common type wave form is the
square wave. Most electronic components are controlled by
a computer PCM, BCM, ECM, ECU or a host of other names.
When the computer turns on a component it usually completes a ground circuit sometime controlling a relay.
Square Wave
15
10
5
0
Normal Square wave.
NOTE: Any wave that is on more than off or off ore than on is called a pulsed wave.
Normal voltage spikes
Pulsed Wave
Pulsed waves are used to control several electrical components such as: Fuel pump Canister solenoids EGR solenoidsWave length: The time required for on complete
cycle of a waveform.
Pulsed Wave
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The difference in wave length is caused by circuit demands
NORMAL PULSE WAVE
Wave length
Pulsed Wave
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Bad pulse wave
Voltage did not drop properly
Voltage did increase properly
Coolant Temperature Sensor(CTS) Most coolant sensors are
Negative Temperature Coefficient (NTC) devices.
The sensor resistance starts out high around 200 Ohms and drops as engine temperature increases.
Bad CTS wave form
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4
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2
1
0
50 100 150 200 250 50 second scale
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Good CTS waveform
Bad CTS wave forms
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50 100 150 200 250 50 second scale
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Bad CTS sensor or electrical connection disconnected waveform
Bad CTS erratic voltage pattern
Crankshaft Sensor This signal should be test
when the engine fail to start due to lack ignition.
The crankshaft sensor produces an AC voltage that is low while cranking and increases after the engine starts.
AC voltage output is critical, low output can prevent an engine from starting. Even if the signal pattern
look good.
Crankshaft Sensor
Normal due to missing tooth on reluctor or flywheel.
The missing tooth is used by the PCM to determine crankshaft position
Crankshaft Sensor
Voltage at start-up Voltage at higher cranking RPM
NOTE: Operating parameters vary from manufactures
Crankshaft Sensor
Engine Running: Note the higher voltage
Crankshaft Sensor
A defective crankshaft sensor will show little or no output on the oscilloscope
Proper output voltage is critical.
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.6
.4
.2
0
.2
.4
Defective Crankshaft sensor
Voltage to LOW
Knock Sensor
A knock sensor is used with some management systems,
The Knock sensor is a small piezo-electrical device. That produces electricity when vibrated.
Knock sensor are used to reduce ignition timing when a spark knock occurs. Usually no more than 10˚ Knock Sensor
Knock Sensor
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4
3
2
1
0
1
Point where knock occurred
50 100 150 200 250 300 350
50 mS scale
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G
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NOTE: Knock sensor output should normally be zero
Knock Sensor
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1
0
Bad knock sensor pattern
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Oscilloscope's
Its important to remember that all electrical wiring will have some type electrical pattern that can be view on an oscilloscope.
Open Circuit
NOTE: Voltage is “0” on an open circuit
Good ground circuit
Oscilloscope's Quiz
1. Technician A says pattern A is DC voltage. Technician B says Pattern B is DC voltage. Who is correct.
A. Technician A only B. Technician B only C. Both A and B D. Neither A nor B
Pattern A
Pattern B
Oscilloscope's Quiz
2. How many seconds pass from point A to Pont B?A. 1B. 2C. 34. 4
1 Second Scale
A B
Oscilloscope's Quiz 3. Technician A says this
pattern is an AC wave form. Technician B says this is DC unfiltered. Who is correct?
A. Technician A Only B. Technician B only C. Both A and B D. Neither A nor B
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1
0
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1
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1
2
Oscilloscope's Quiz
4. What is peak Negative voltage in this pattern? A. - 1 volt B. - 2 volts C. - 4 volts D. -.25 volts
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1
2
50 100 150 200
Oscilloscope's Quiz
5. What is peak to peak voltage in this pattern? A. 1 volt B. 2 volts C. 4 volts D. .25 volts
2
1
0
1
2
50 100 150 200
Oscilloscope's Quiz
6. The number of complete cycles per second measured is: A. Amperage B. Frequency C. Ohms D. Voltage
Oscilloscope's Quiz 7. Technician A says voltage
is measured from point A - B. Technician B says Time is measure from point C-D. Who is correct?A. Technician A onlyB. Technician B onlyC. Both A and BD. Neither A nor B
A
B C D
Oscilloscope's Quiz
8. What time scale is this oscilloscope set for? A. 2 mS B. 5 mS C. 10 mS D. 100 mS
Oscilloscope's Quiz
9. Technician A says the wave form is of a defective TPS (Throttle position sensor) Technician B says the pattern is of a good CTS sensor. Who is correct? A. Technician A only B. Technician B only C. Both A and B D. Neither A nor B
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4
3
2
1
0
50 Second Scale50 100 150 200 250
Oscilloscope's Quiz
10. Which diagram is of a good ground circuit? A. 1 B. 2 C. 3 D. 4
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