how to test the rear o2 heater

7/23/2019 How to Test the Rear O2 Heater

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How to Test the Rear O2 Heater -P0141(1998-2002 1.8L Corolla)

OXYGE !E!OR "#$GO!#!

O2 sensors are amazingly rugged considering the operating environment they live in. But O2 sensorsdo wear out and eventually have to be replaced.

The performance of the O2 sensor tends to diminish with age as contaminants accumulate on thesensor tip and gradually reduce its ability to produce voltage. This kind of deterioration can be causedby a variety of substances that find their way into the exhaust such as lead, silicone, sulfur, oil ashand even some fuel additives. The sensor can also be damaged by environmental factors such aswater, splash from road salt, oil and dirt.

s the sensor ages and becomes sluggish, the time it takes to react to changes in the air!fuel mixtureslows down which causes emissions to go up. This happens because the flip"flopping of the fuelmixture is slowed down which reduces converter efficiency. The effect is more noticeable on engineswith multiport fuel in#ection $%&'( than electronic carburetion or throttle body in#ection because thefuel ratio changes much more rapidly on %&' applications.

'f the sensor dies altogether, the result can be a fixed, rich fuel mixture. )efault on most fuel in#ectedapplications is mid"range after three minutes. This causes a big #ump in fuel consumption as well asemissions. nd if the converter overheats because of the rich mixture, it may suffer damage.

One *+ study found that - of the vehicles that failed an '!% 2/- emissions test needed a new O2sensor.

%ost O2 sensor problems will cause the OB) '' system to set one or more diagnostic trouble codes$)T0s( and turn on the 0heck *ngine light. These are the OB) codes associated with O2 sensorfaults1

+---....3O24 3eater 0ontrol 0ircuit Bank 5 4ensor 5

+--5....3O24 3eater 0ontrol 0ircuit 6ow Bank 5 4ensor 5+--2....3O24 3eater 0ontrol 0ircuit 3igh Bank 5 4ensor 5+--....Turbo 0harger Bypass 7alve 0ontrol 0ircuit+--/....Turbo 0harger Bypass 7alve 0ontrol 0ircuit 6ow+--8....Turbo 0harger Bypass 7alve 0ontrol 0ircuit 3igh+--9....3O24 3eater 0ontrol 0ircuit Bank 5 4ensor 2+--....3O24 3eater 0ontrol 0ircuit 6ow Bank 5 4ensor 2+--:....3O24 3eater 0ontrol 0ircuit 3igh Bank 5 4ensor 2+--/2....3O24 3eater 0ontrol 0ircuit Bank 5 4ensor +--/....3O24 3eater 0ontrol 0ircuit 6ow Bank 5 4ensor +--//....3O24 3eater 0ontrol 0ircuit 3igh Bank 5 4ensor +--8-....3O24 3eater 0ontrol 0ircuit Bank 2 4ensor 5+--85....3O24 3eater 0ontrol 0ircuit 6ow Bank 2 4ensor 5+--82....3O24 3eater 0ontrol 0ircuit 3igh Bank 2 4ensor 5+--89....3O24 3eater 0ontrol 0ircuit Bank 2 4ensor 2+--8....3O24 3eater 0ontrol 0ircuit 6ow Bank 2 4ensor 2+--8:....3O24 3eater 0ontrol 0ircuit 3igh Bank 2 4ensor 2+--92....3O24 3eater 0ontrol 0ircuit Bank 2 4ensor +--9....3O24 3eater 0ontrol 0ircuit 6ow Bank 2 4ensor +--9/....3O24 3eater 0ontrol 0ircuit 3igh Bank 2 4ensor +-5-....O2 4ensor 0ircuit Bank 5 4ensor 5

+-55....O2 4ensor 0ircuit 6ow 7oltage Bank 5 4ensor 5+-52....O2 4ensor 0ircuit 3igh 7oltage Bank 5 4ensor 5+-5....O2 4ensor 0ircuit 4low ;esponse Bank 5 4ensor 5+-5/....O2 4ensor 0ircuit


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+-5:....O2 4ensor 0ircuit 3igh 7oltage Bank 5 4ensor 2+-5=....O2 4ensor 0ircuit 4low ;esponse Bank 5 4ensor 2+-5/-....O2 4ensor 0ircuit


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ny O2 sensor that is defective obviously needs to be replaced. But there may also be benefits toreplacing the O2 sensor periodically for preventative maintenance. ;eplacing an aging O2 sensorthat has become sluggish can restore peak fuel efficiency, minimize exhaust emissions and prolongthe life of the converter.

Anheated 5 or 2 wire wire O2 sensors on 5=9 through early 5==-s vehicles can be replaced every-,--- to 8-,--- miles. 3eated and /"wire O2 sensors on mid"5=:-s through mid"5==-sapplications can be changed every 9-,--- miles. On OB) '' e@uipped vehicles $5==9 up(, areplacement interval of 5--,--- miles can be recommended.

The oxygen sensor can be removed from the exhaust manifold using a special oxygen sensor socket$which has a cutout to clear the wires(, or a 22mm socket. The sensor will come out easier if the

engine is slightly warm but not hot to the touch. +lace the socket over the sensor and turncounterclockwise to loosen it. 'f it is frozen, apply penetrating oil and heat around the base of thesensor.

Chen installing a new Ddirect fitD or O*% oxygen sensor, the wiring connector on the new sensor willplug into the connector with no modifications needed. But if you are installing a DuniversalD oxygensensor, the original wiring connector will have to be cut off so the wires on the new sensor can bespliced to the wires that went to the connector. Cith /"wire sensors, one wire is the signal wire, one isground, and the other two are for the heater circuit. The wires are color coded, but the colors on theuniversal sensor probably won?t match those on the original sensor. 4ee the chart below from thecolor coding used on various brands of oxygen sensors1


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Typical oxygen sensor wiring color codes.

Oxygen 4ensor E How &a' o*e' se'sors are o' to+a,s e'*'es

't depends on the model year and type of engine. On most four and straight six cylinder engines,there is usually a single oxygen sensor mounted in the exhaust manifold. On 79, 7: and 75-engines, there are usually two oxygen sensors, one in each exhaust manifold. This allows the

computer to monitor the air!fuel mixture from each bank of cylinders.

On later model vehicles with OB) '' $some 5== and ?=/ models, and all 5==8 and newer models(,one or two additional oxygen sensors are also mounted in or behind the catalytic converter to monitorconverter efficiency. These are referred to as the downstream O2 sensors, and thee will be one foreach converter if the engine has dual exhausts with separate converters.

How are the o*e' se'sors +e't/e+ o' a sa' tool

Chen displayed on a scan tool, the right and left upstream oxygen sensors are typically labeled Bank5, 4ensor 5 and Bank 2, 4ensor 5. The Bank 5 sensor will always be on the same side of a 79 or 7:engine as cylinder number one.

On a scan tool, the downstream sensor on a four or straight six cylinder engine with single exhaust istypically labeled Bank 5, 4ensor 2. On a 79, 7: or 75- engine, the downstream O2 sensor might belabeled Bank 5 or Bank 2, 4ensor 2. 'f a 79, 7: or 75- engine has dual exhausts with dualconverters, the downstream O2 sensors would be labeled Bank 5, 4ensor 2 and Bank 2, 4ensor 2.Or, the downstream oxygen sensor might be labeled Bank 5 4ensor if the engine has two upstreamoxygen sensors in the exhaust manifold $some do to more accurately monitor emissions(.

't?s important to know how the O2 sensors are identified because a diagnostic trouble code thatindicates a faulty O2 sensor re@uires a specific sensor to be replaced. Bank 5 4ensor 5 might be theback O2 sensor on a transverse 79, or it might be the one on the front exhaust manifold. Chat?smore, the O2 sensors on a transverse engine might be labeled differently than those on a rear"wheel

drive application. There is not a lot of consistency as from one vehicle manufacturer to another as tohow O2 sensors are labeled, so always refer to the O*% service literature to find out which sensor isBank 5 4ensor 5 and which one is Bank 2 4ensor 5. This information can be difficult to find. 4omeO*%s clearly identify which O2 sensor is which but others do not. 'f in doubt, call a dealer and asksomebody in the service department.

&or Oxygen 4ensor 6ocations, 0lick 3ere.
http://www.aa1car.com/library/oxygen_sensor_locations.htmhttp://www.aa1car.com/library/oxygen_sensor_locations.htm


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How +oes a +ow'strea& O2 se'sor &o'tor o'erter e//e'

downstream oxygen sensor in or behind the catalytic converter works exactly the same as anupstream O2 sensor in the exhaust manifold. The sensor produces a voltage that changes when theamount of unburned oxygen in the exhaust changes. 'f the O2 sensor is a traditional zirconia typesensor, the voltage output drops to about -.2 volts when the fuel mixture is lean $more oxygen in theexhaust(. Chen the fuel mixture is rich $less oxygen in the exhaust(, the sensor?s output #umps up toa high of about -.= volts. The high or low voltage signal tells the +0% the fuel mixture is rich or lean.

On some newer vehicles, a new type of Cide ;atio ir &uel $C;&( 4ensoris used. 'nstead ofproducing a high or low voltage signal, the signal changes in direct proportion to the amount ofoxygen in the exhaust. This provides a more precise measurement for better fuel control. Thesesensors are also called wideband oxygen sensors because they can read very lean air!fuel mixtures.

The OB) '' system monitors converter efficiency by comparing the upstream and downstreamoxygen sensor signals. 'f the converter is doing its #ob and is reducing the pollutants in the exhaust,the downstream oxygen sensor should show little activity $few lean"to"rich transitions, which are also

called DcrosscountsD(. The sensor?s voltage reading should also be fairly steady $not changing up ordown(, and average -./8 volts or higher.

'f the signal from the downstream oxygen sensor starts to mirror that from the upstream oxygensensor$s(, it means converter efficiency has dropped off and the converter isn?t cleaning up thepollutants in the exhaust. The threshold for setting a diagnostic trouble code $)T0( and turning on the%alfunction 'ndicator 6amp $%'6( is when emissions are estimated to exceed federal limits by 5.8times. 4ee Troubleshooting a +-/2- 0atalyst 0odefor more info about converter problems.

'f converter efficiency had declined to the point where the vehicle may be exceeding the pollutionlimit, the +0% will turn on the %alfunction 'ndicator 6amp $%'6( and set a diagnostic trouble code. tthat point, additional diagnosis may be needed to confirm the failing converter. 'f the upstream and

downstream O2 sensors are functioning properly and show a drop off in converter efficiency, theconverter must be replaced to restore emissions compliance. The vehicle will not pass an OB) ''emissions test if there are any converter codes in the +0%.

hat,s the +//ere'e 3etwee' a heate+ a'+ 5'heate+ o*e' se'sor

3eated oxygen sensors have an internal heater circuit that brings the sensor up to operatingtemperature more @uickly than an unheated sensor. n oxygen sensor must be hot $about 9-- to 98-degrees &( before it will generate a voltage signal. The hot exhaust from the engine will provideenough heat to bring an O2 sensor up to operating temperature, but it make take several minutesdepending on ambient temperature, engine load and speed. )uring this time, the fuel feedbackcontrol system remains in Dopen loopD and does not use the O2 sensor signal to ad#ust the fuelmixture. This typically results in a rich fuel mixture, wasted fuel and higher emissions.

By adding an internal heater circuit to the oxygen sensor, voltage can be routed through the heater assoon as the engine starts to warm up the sensor. The heater element is a resistor that glows red hotwhen current passes through it. The heater will bring the sensor up to operating temperature within2- to 9- seconds depending on the sensor, and also keep the oxygen sensor hot even when theengine is idling for a long period of time.

3eated O2 sensors typically have two"three or four wires $the extra wires are for the heater circuit(.


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Testing trouble code P01416 Heated Oxygen Sensor Circuit (Sensor #2)on your 5.:6 Toyota

0orolla involves two basic tests. These two are1 making sure the rear O2 sensor?s heater is getting

power and ground, and then checking the heater?s internal resistance.

These two tests can be easily accomplished with only a multimeter. >es, that?s right, you don?t need

an expensive scan tool to test the rear oxygen sensor?s heaterF

OTE6This oxygen sensor is known by several different names1

5. ;ear 3eated Oxygen $O2( 4ensor.

2. 3O24 5!2.

. )ownstream Oxygen $O2( 4ensor.

/. Oxygen 4ensor Bank 5 4ensor 2.

8. +ost"0atalytic 0onverter O2 4ensor.

3ere are the contents of this tutorial1

0ircuit )escriptions of the )ownstream Oxygen 4ensor.

T*4T 51 7erifying the 3eater *lement is Getting +ower and Ground.

T*4T 21 Testing the 3eater *lement?s ;esistance.

Chere to Buy the Oxygen 4ensor and 4ave 4ome HHH.

%ore 5.:6 Toyota )iagnostic Tutorials.

OTE6'f you need to test the front oxygen sensor?s heater $or trouble code1 P017(, see this tutorial1

ro't O*e' !e'sor Heater Test -P017 (1998-2002 1.8L Toota Corolla) .
http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-1#1http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-1#2http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2#1http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2#1http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2#2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-1http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-1#1http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-1#2http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2#1http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-2#2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-1


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Cr5t "esr:to's o/the "ow'strea& O*e' !e'sor

The rear oxygen sensor is e@uipped with an internal heater $#ust like the front one(. The heater?s #ob

is to get the O2 sensor to its operating temperature fast and keep it there thru? all engine operation

conditions $especially engine idle(.

4ince the O2 sensor has / wires sticking out of it, you and ' need to know what wires do what to be

able to test it. 4o, in the table below you?ll find the color of the wires of the engine wiring harness

oxygen sensor connector for the rear oxygen sensor.

One last thing you need to know1 0hecking for power and ground is done on the O2 sensor?s engine

wiring harness connector. This connector has female terminals. Testing the heater?s resistance is

done on the O2 sensor?s connector itself... and this connector has male terminals.

Downstream Oxygen Sensor (HO2S 12) Pinout(1998-2002 1.8L Toyota oro!!a)

Pin "ire o!or Des#ri$tion

1 P%& Heater 'roun (-)

2 L& Heater Power (*)

+ ,D O2 Signa!

,% O2 Signa! 'roun

TE!T 16;er/'* the Heater

Ele&e't s Gett'* Power a'+ Gro5'+


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The rear oxygen sensor?s heater needs battery power and ground to heat up the O2 sensor. 4o the

first thing we?ll do, in our P0141diagnostic, is verify that they?re being fed to the rear O2 sensor?s

heater.

The 2 wires that we need to check are1

The black $T#O6Be careful and test the O2 sensor with a completely cold engineF The O2 sensor and the

exhaust pipe it?s bolted into gets extremely hot and stays hot long after the engine has been turned

off. Be careful and take all necessary safety precautionsF lso, don?t trust the #ack to keep your

0orolla up in the air "place it on #ack standsF

#%PORT$T6The illustration of the connector above is of the connector on the oxygen sensor itself.

To check for power and ground you?ll test the connector of the engine wiring harness sensor $which

has female terminals(.

OI, this is what you?ll need to do1

1.1

Loate the +ow'strea& o*e' se'sor a'+ +so''et t /ro& ts e'*'e

wr'* har'ess o''etor.

2.2

!et o5r &5lt&eter to ;olts "C &o+eand turn the key On but don?t crank or

start the engine $this will power up the O2 sensor?s engine wiring harness

connector(.


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3.3

th o5r &5lt&eter test lea+s? :ro3e the /e&ale ter&'als that orres:o'+

to the 3la@ a'+ :'@ wres o/ the o''etor.

;emember, you?re testing the engine wiring harness O2 sensor connector $which

has female terminals( and not the connector of the O2 sensor itself.

4.4

th the =e O' E'*'e O// (=OEO)? o5r &5lt&eter sho5l+ re*ster 10 to

12 ;olts "C.

6et?s take a look at your test results1

C$!E 16Yo5r &5lt&eter re*stere+ 10 to 12 ;olts "C-Good, since this confirms that the rear

oxygen sensor?s heater element is getting power and ground.

The next step is to verify that your Toyota 0orolla?s rear oxygen sensor heater?s resistance is within

specification. &or this resistance test, go to T*4T 21 Testing the 3eater *lement?s ;esistance.

C$!E 26Yo5r &5lt&eter "#" OT re*ster 10 to 12 ;olts "C- The most likely cause is that power

is missing due to a blown fuse or a short $or open( in the wiring. >ou?ll need to check the fuse in the

fuse box and make sure it?s not blown.

'f the fuse is OI, your next step is to find out why this battery power $or ground( is missing using a

wiring diagram.

TE!T 26Test'* the Heater Ele&e't,s Ressta'e


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'f the resistance is out of specification a'+you?ve verified that power and ground are reaching the

rear O2 sensor?s heater... then you can conclude that it?s fried and the whole sensor needs to be

replaced.

OTE6Just a reminder that the oxygen sensor has to be completely cold before proceeding with this

test.... since the manual calls for the O2 sensor to be at room temperature for the resistance test.

OI, this is what you need to do1

1.1

Loate the O2 se'sor ter&'als '5&3er 1 a'+ '5&3er 2of the O2 sensor

connector itself $not the engine wiring harness O2 connector(.

2.2

th o5r &5lt&eter ' Oh&s &o+e... :ro3e ter&'als '5&3er 1 a'+'5&3er 2 o/ the O2 se'sor tsel/.

3.3

#/ all s O=? o5 sho5l+ see a3o5t 11 to 1A Bson your multimeter.

'f the heater element is fried, your multimeter will show an open $usually indicated

by the letters O6( or a number over 5- I Ks.

6et?s take a look at your test results1

C$!E 16Yo5r Corolla,s rear O2 heater,s ressta'e s wth' /ator s:e/ato'-This test

result tells you that the rear O2?s heater is OI.

C$!E 26Yo5r &5lt&eter showe+ a' o:e' r5t (OL)- This confirms that the rear O2?s heater

element, on your 0orolla, is fried. ;eplacing the rear oxygen sensor with a new one will solve the

+-5/5 trouble code lighting up the check engine light $0*6(.

Taking into account that you have1

'n T*4T 5you verified power and ground is reaching the sensor?s heater.

-$"-

'n this test you have confirmed that the heater element?s resistance is out ofspecification.

... >ou can correctly conclude that your 5.:6 Toyota 0orolla downstream O2 sensor needs to be

replaced with a new one.

here to


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OTE6'f you?re not sure if the above O2 sensor fit your particular 5.:6 Toyota 0orolla don?t worry...

once you get to the site, they?ll make sure the sensor switch is the right one, if not, they?ll find you the

right one.

How To Test the TP !e'sor(1998-2002 1.8L Toota)

October 5, 2-5>:+ate+6January 5-, 2-58rtte' 36braham Torres"rredondo$rtle #+6859

Page 1

Page 2

Page 3

The throttle position sensor $T+4( on your 5==:"2--2 5.:6 e@uipped Toyota 0orolla can be easily

tested with #ust a multimeter.


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Chere to Buy the T+4 and 4ave.

5.:6 Toyota Tutorials.

our ToyotaLs +0% receives this throttle angle info on the middle wire. The other two provide power

and ground $to the T+4(.

'n the table below, youLll find a short description of what each wire does1

1.8L Toyota oro!!a TPS ir#uits(2001/ 2002/ 200+/ 200/ 200/ 200/ 200)


1 3L 4o!ts

2 ,% Sensor 'roun

+ LT ',% T5rott!e Position Signa!

TE!T 16Che@'* theThrottle Posto' !e'sor (TP!) !*'al
http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-3http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-3#2http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-3http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-3#2


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The throttle position sensor $T+4( sends the throttle plate angle voltage signal $it creates as the

throttle plate opens and closes( on the 6T G;< $light green( wire.

4o, in this test section, youLll tap into this 6T G;< wire and manually open and close the throttle plate

to see if the T+4 is creating an increasing!decreasing voltage signal.

'f the T+4 is bad on your Toyota 0orolla... then the voltage output will stay stuck at one value no

matter how much you open or close the throttle plate.

'f the T+4 is OI, then the voltage output of the sensor will increase!decrease as you manually

open!close the throttle plate.

#%PORT$T6This is an on car test of the sensor and the throttle position sensor must remain

connected to its harness connector.

3ere are the test steps1

1.1

Plae o5r &5lt&eter ' ;olts "C &o+e a'+ o''et the re+ test lea+ to the

LT GR wreof the T+ sensor harness connector.

OTE6The T+ sensor connector needs to be connected to the T+4, so you?ll

need to either back"probe the connector or use a wire piercing probe to get to the

signal inside the wire $to see what a wire piercing probe looks like1 Cire +iercing

+robe Tool(.

2.2

Gro5'+ the 3la@ &5lt&eter lea+directly on the battery negative $"( post.

t this point $with the throttle plate closed( your multimeter should read a voltage

between -. to 5.- volt )0.

3.3

%a'5all rotate the throttle.

>ou?ll get the best results by opening and closing the throttle directly on the

throttle body instead of stepping on the accelerator pedal.
http://troubleshootmyvehicle.com/Index-of-Tool-Reviews/wire-piercing-probehttp://troubleshootmyvehicle.com/Index-of-Tool-Reviews/wire-piercing-probehttp://troubleshootmyvehicle.com/Index-of-Tool-Reviews/wire-piercing-probehttp://troubleshootmyvehicle.com/Index-of-Tool-Reviews/wire-piercing-probe


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4.4

The &5lt&eter sho5l+ show a' 'reas'* olta*eas you $or your helper(

open up the throttle.

Cith the throttle plate completely open, your multimeter should read1 .2 to /.=

7olts )0.

>ou?ll get the best results by opening and closing the throttle directly on the

throttle body instead of stepping on the accelerator pedal.

5.5

The &5lt&eter sho5l+ show a +ereas'* olta*eas you begin to close the

throttle.

6.6

>s'* a srew+rer,s ha'+le? *e'tl ta: the TP se'soras you open and

close the throttle and observer the multimeter.

The purpose $of tapping the T+ sensor with the screwdriver?s handle( is to see if

the T+ sensor shows gap?s in the voltage signal. ChyM Because a good T+

sensor will show a continuous increasing or decreasing voltage signal even while

getting tapped by the screw"driver?s handle.

C$!E 16The TP se'sor s*'al,s olta*e 'rease+ a'+ +erease+ s&oothl a'+ wtho5t *a:s.

This tells you that the T+4 on your Toyota 0orolla is working and not defective.

This test result also tells you that1

5. 0ircuit N5 is providing power.

2. 0ircuit N2 is providing ground.

C$!E 26The TP se'sor s*'al,s olta*e ++ 'ot 'rease or +erease. 'n the ma#ority of the

cases this T+4 result tells you that the sensor is bad. But not always.

To be sure that the T+4 is truly fried, we need to do 2 more tests. These tests involve checking that

the sensor is getting both power and ground. &or the first of these two tests, go to T*4T 21 0hecking

Throttle +osition 4ensor $T+4( +ower.

C$!E 76The TP se'sor s*'al,s olta*e showe+ *a:s ' ts olta*e o5t:5t as o5 ta::e+ the

se'sor wth the srew+rer. 'f the gaps in the multimeterLs voltage readings only showed up when

you were tapping on the T+4 $with the screwdriverLs handle( then this test result tells you that the

T+4 is bad and needs to be replaced.

TE!T 26Che@'* ThrottlePosto' !e'sor (TP!) Power
http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-2http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-2http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-2http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-2


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>our ToyotaLs +0% feeds the throttle position sensor with 8 volts )0 thruL the >*6 $yellow( wire.

This voltage can be easily verified with your multimeter and thatLs exactly what weLll do in this test

section.

OTE6>ouLll be checking for this voltage on the sensorLs harness connector... but you should avoid

probing the connectors front terminals. 'nstead, you should back"probe the connector with the

appropriate tool or use a wire"piercing probe.

Cith the multimeter in 7olts )0 mode, this is what you need to do1

1.1

Co''et the re+ &5lt&eter test lea+ to the YEL wre o/ the TP! har'ess

o''etor

This is the wire that connects to the terminal labeled with the '5&3er 7.

2.2

Gro5'+ the 3la@ &5lt&eter lea+ +retl o' the 3atterDs 'e*ate

ter&'al.

3.3

Hae a hel:er t5r' the @e to the O' :osto'? 35t +o'Dt ra'@ or start thee'*'eafter the multimeter leads have been set up.

4.4

Yo5r &5lt&eter sho5l+ re*ster 4. to olts "Cif the >*6 wire is feeding the

throttle post ion sensor $T+4( with power.

C$!E 16The &5lt&eter re*stere+ 4. to olts "C. This is the correct and expected test result.

>our next step is to make sure that the T+4 is getting ground on the B;< $brown( wire. &or this test,

go to1 T*4T 1 0hecking Throttle +osition 4ensor $T+4( Ground.

C$!E 26The &5lt&eter "#" OT re*ster 4. to olts "C. ;e"check your multimeter lead

connections and re"test. 'f the multimeter still does not show the indicated voltage, then youLve found

the reason why the T+4 did not create a voltage signal in T*4T 5.
http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-2#2http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-1#3http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-2#2http://troubleshootmyvehicle.com/toyota/1.8L/throttle-position-sensor-test-1#3


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lthough itLs beyond the scope of this tutorial to find the reason why these 8 volts are missing... youLll

need to get yourself a wiring diagram $for your particular mini"van( and check the continuity of this

wire between the T+4 and the +0%.

TE!T 76Che@'* ThrottlePosto' !e'sor (TP!) Gro5'+

*6 wire, in

this test section youLll verify that the B;< $brown( wire of the T+4 harness connector is providing

ground.

To confirm that this B;< wire is feeding ground, weLll do another voltage test with the multimeter.

OTE6Be careful and do not short this wire to battery voltage, or youLll fry your ToyotaLs +0%.

These are the test steps1

1.1

Co''et the 3la@ &5lt&eter test lea+ to the


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C$!E 16The &5lt&eter re*stere+ 12 olts "C. This tells you that the T+4 is getting ground. ou have confimed that the T+4 is not creating a throttle plate angle voltage signal$T*4T 5(.

2. >ou have confirmed that it is getting power $T*4T 2(.

nd in this test step you have confirmed that the throttle position sensor is getting ground... then you

can conclude that the reason its not creating a throttle plate angle signal is because it is defective

and needs to be replaced.

C$!E 26The &5lt&eter "#" OT re*ster 12 olts "C. ;e"check your multimeter lead

connections and re"test. 'f the multimeter still does not show the indicated voltage, then youLve found

the reason why the T+4 did not create a voltage signal in T*4T 5.

lthough itLs beyond the scope of this tutorial to find the reason why this ground is missing... youLll

need to get yourself a wiring diagram $for your particular Toyota( and check the continuity of this wire

between the T+4 and the +0%.

ro't O*e' !e'sor Heater Test -P017(1998-2002 1.8L Toota Corolla)

January 5-, 2-58>:+ate+6&ebruary 5, 2-58

rtte' 36braham Torres"rredondo$rtle #+69/:

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Chen trouble code P0176 Heate+ O*e' !e'sor Cr5t (!e'sor F1)sets, it usually signals a

problem with the internal heater of the upstream oxygen sensor.

Thankfully, you can easily diagnose this trouble code without any expensive diagnostic test

e@uipment... all you need is a multimeter. 'n this tutorial, '?ll show you the basic tests you?ll need to

perform to diagnose the upstream sensor as good or bad.

OTE6This oxygen sensor is known by several different names1

5. &ront 3eated Oxygen $O2( 4ensor.

2. 3O24 55.

. Apstream Oxygen $O2( 4ensor.

/. Oxygen 4ensor Bank 5 4ensor 5.

8. +re"0atalytic 0onverter O2 4ensor.

3ere are the contents of this tutorial1

0ircuit )escriptions of the Apstream Oxygen 4ensor.

T*4T 51 7erifying the 3eater *lement is Getting +ower.

T*4T 21 7erifying the 3eater *lement is Getting Ground.

T*4T 1 Testing the 3eater *lement?s ;esistance.

Chere to Buy the Oxygen 4ensor and 4ave 4ome HHH.

%ore 5.:6 Toyota )iagnostic Tutorials.

OTE6'f you need to test the rear oxygen sensor?s heater $or trouble code1 P0141(, see this tutorial1

How to Test the Rear O2 Heater -P0141 (1998-2002 1.8L Corolla).

Cr5t "esr:to's o/the >:strea& O*e' !e'sor
http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-1#1http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-1#2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-2#2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-3#1http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-3#1http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-3#2http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-1http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-1#1http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-1#2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-2#2http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-3#1http://troubleshootmyvehicle.com/toyota/1.8L/code-p0135-diagnostic-tests-3#2http://troubleshootmyvehicle.com/toyota/1.8L/rear-oxygen-sensor-heater-tests-1


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s you?re already aware, your 5.:6 Toyota 0orolla uses 2 oxygen sensors. One is located located

before the catalytic converter and the second one is located after it.

Both sensor?s are e@uipped with an internal heater and thus have / wires sticking out of them.

2 wires are for actual oxygen sensing part of the sensor assembly. The other 2 are to supply the

heater with power and ground.

Below, you?ll find the color of the wires of the engine wiring harness oxygen sensor connector for

sensor HO2! 111

6$stream Oxygen Sensor (HO2S 11) Pinout(1998-2002 1.8L Toyota oro!!a)


1 P%& Heater 'roun (-)

2 L& Heater Power (*)

+ "HT O2 Signa!

,% O2 Signa! 'roun

TE!T 16;er/'* the Heater Ele&e't s Gett'* Power


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To get our +-58 trouble code diagnostic under way, we?re gonna? start by making sure that the

upstream O2 sensor?s heater is getting power. Then, after confirming power, we?re gonna? make sure

it?s getting ground in T*4T 2.

The black $T#O6+erform all of the oxygen sensor tests with a completely cold engine. The O2 sensor gets

extremely hot and stays hot long after the engine has been turned off. Be careful and take all

necessary safety precautionsF lso, if you raise your vehicle with a #ack, place it on #ack stands.

#%PORT$T6The illustration of the connector above is of the connector on the oxygen sensor itself.

To check for power, you need to test the


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recommendation here1 Buying a )igital %ultimeter for utomotive )iagnostic

Testing$at1 easa5to+a*'osts.o&(.

4.4

th the =e O' E'*'e O// (=OEO)? the


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Ce?ll check for ground by doing a simple multimeter voltage test very much like the one we did in

T*4T 5.

OTE6The illustration of the connector above is of the connector on the oxygen sensor itself. To

check for ground, you need to test the P=wire of the engine wiring harness sensor connector.

These are the test steps1

1.1

Loate the P= wreof the O2 sensor?s engine wiring harness connector.

OTE6;emember, you?ll test the wire that?s on the engine wiring harness

connector side and


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OI, now that you?ve checked the basics $power and ground( we?re gonna? check the O2 sensor?s

heater element?s resistance and see if it?s within specification.

'f your test shows that the O2 sensor?s heater?s resistance '4


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C$!E 16The O2 heater,s ressta'e s wth' /ator s:e/ato'-This test result tells you that

the 3O24 55?s heater is OI.

C$!E 26Yo5r &5lt&eter showe+ a' o:e' r5t (OL)- This confirms that the 3O24 55?s heater

element is fried. ;eplacing the 3O24 55 with a new one will solve the +-58 trouble code lighting up

the check engine light $0*6(.

Taking into account that you have1

0onfirmed that the upstream O2 sensor?s heater element is getting power $T*4T 5(.

-$"-

0onfirmed that the upstream O2 sensor?s heater element is getting ground $T*4T 2(.

-$"-

'n this test you have confirmed that the heater element?s resistance is out of

specification.

... >ou can correctly conclude that your 5.:6 Toyota 0orolla upstream O2 sensor needs to be

replaced with a new one.

How to Test the %$ !e'sor(Toota Corolla 1.8L)

July 28, 2-5>:+ate+6


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To help you navigate this article, here are its main points1

4ymptoms of a B) %& 4ensor.

Chat Tools )o '


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'f you need to upgrade or buy a multimeter, check out my recommendation1be?s %ultimeter ;ecommendation$found at1 easa5to+a*'osts.o&(.

2. Cire piercing probe.

lthough this tool is not an absolute must, if you do buy one, you?ll realize #usthow easy it makes testing the voltages inside the wires.

'f you need to see what this tool looks like, you can see it here1 Cire +iercing+robe.

scan tool comes in handy... but you won?t need it to use the testing info in this article.

hat "oes the %$ !e'sor "o

The %& sensor is tasked with measuring the amount of air entering the engine at any given ;+%.

The +0% $Powertrain Control %odule Q &uel 'n#ection 0omputer( then uses this measurement of air

flow to in#ect the correct amount of fuel.

To get into more specifics1 The %& sensor informs the +0% the amount of air flow entering the

engine by converting the measurement of air into a voltage signal that increases with more air flow

$as you accelerate the engine( or decreases as the engine breathes less air.

This is the key to understanding how to %& sensor works and how to test it. '?ll repeat it once more1

The more air the engine breathes, the bigger the voltage signal the %& sensor creates. The less air

the engine breathes, the smaller the voltage signal the %& sensor sends the +0%.

3ereLs what it looks like on a multimeter1

t an idle under 5--- ;+%?s the %& sensor outputs about 5.5 7olts )0.

t about 58-- ;+%?s the math signal output is about 5.2 volts )0.

sk about --- ;+%?s the %& signal output is about 5. volts )0.

;emember, the important thing to know, is that at higher ;+%s, when the engine is breathing more

air, the %& signal $in voltage( is greater than when the engine is idling.


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7 Sensor onne#tor Pin Out


1 !a#: use $ower (12 4o!ts)

2 !ue w; "5ite stri$e 7 sensor groun (P7)

+ 'reen 7 sensor signa!

3e!!ow w; !a#: stri$e ou can use a 52 7olt automotive test light or a multimeter to confirm wire N5 is feeding 5- to

52 volts to the %& sensor. lthough the test instructions below assume that you?ll be using a

multimeter.

OI, this what you?ll need to do1

5. +lace the multimeter in 7olts )0 %ode.


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2. 6ocate the wire identified with the '5&3er 1.

This is the


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2. 6ocate the wire identified with the '5&3er 2.

This is the


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This is the Gree'wire of the %& sensor connector.

0onnect the ;*) multimeter lead to this Gree'wire using an appropriate tool$like a Cire +iercing +robe(.

. ground the B60I lead of the multimeter directly on the battery negative $"( terminal.

/. 0rank and start the engine.

8. 'f the engine is cold, let it warm up a bit so that the idle will settle down a bit.

9. >our multimeter should register1

round 5.5 7olts )0 at idle.

s you accelerate the engine, the voltage values should increase.

o t around 2--- ;+%Ls your multimeter should register about 5 .8 volts )0.

o t around --- ;+%Ls your multimeter should register about 5 . volts )0.

o OTE6;emember these voltage numbers only serve as aguideline. The actual numbers you %& sensor outputs may bea little different. Chat you?re looking for is for the voltage toincrease as you rev up the engine.

Chen you release the accelerator, and the engine returns to idle, the voltage

value should return to somewhere close to 5.5 volts )0.

C$!E 16The &5lt&eter re*stere+ the '+ate+ olta*e al5eswhen you accelerated and

decelerated the engine. This is the correct and expected test result and tells you that the mass air

flow $%&( sensor is good.

'f the mass air flow $%&( sensor were bad, the voltage would have not gone up or down as you

revved the engine up and down.

There?s no need to replace the %& sensor, since this test confirms that it?s functioning.

C$!E 26The &5lt&eter "#" OT re*ster the '+ate+ olta*e al5eswhen you accelerated

and decelerated the engine1 "%ake sure that you?re testing the correct wire, that your connections are

OI, and repeat the test.

'f you still don?t see the voltage values going up when you accelerate the engine or go down when

you decelerate the engine, then you?ve got a B) mass air flow $%&( sensor on your hands.

;eplace the %& sensor.

%$ Test !5&&ar

The key to successfully diagnosing your Toyota?s mass air flow $%&( sensor is knowing that as the

;+%?s go up, so does the voltage signal that the sensor reports to the +0% on the wire labeled with

the '5&3er 7$in the photos in the image viewer(.
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lso, when the %& sensor on your Toyota fails, it usually fails in one of two ways1

5. 't?ll stop producing a voltage signal, even tho? it?s getting power and ground.

2. Or, it?ll produce a signal but this signal won?t go up or down as you accelerate ordecelerate the engine.

'?m pointing this out, because you don?t need to know a precise voltage number for a specific ;+%. '

know, ' know... it would be great to have a specific value to compare against... but trust me, you don?tneed it.

'f in T*4T , the voltage values went up and down... the %& on your 5.:6 e@uipped Toyota vehicle

is OI.

'f indeed the %& sensor is fried on your vehicle, take a look at the %& sensor offers below and

compare. >ou #ust might save a few bucks

How to Test the 5el P5&: #' 2 Tests(4.0L ee:)

%arch -, 2-58>:+ate+6%arch -, 2-58rtte' 36braham Torres"rredondo$rtle #+69:8

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bad fuel pump, that has stopped sending fuel to the fuel in#ectors, will cause a Pcranks but does not

start conditionL on your /.-6 e@uipped Jeep.

fuel pump that is working, but not sending enough volume and therefore not producing enough fuel

pressure, will cause severe drive"ability issues.

The cool thing is that it?s easier than Pa hot knife cutting through butterL to test the fuel pump?s

pressure and!or check a lack of fuel condition causing a no start condition.
http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-2http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/fuel-pump-tests-2


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'n this tutorial '?ll show you the 2 basic tests you?ll need to do to check the condition of your Jeep?s

fuel pump.

0ontents of this tutorial at a @uick glance1

4ymptoms of a Bad &uel +ump.

T*4T 51 Asing 4tarting &luid To 0onfirm 6ack of &uel.

T*4T 21 0hecking &uel +ressure Cith a &uel +ressure Gauge.

Chere to Buy a &uel +ressure Test Gauge.

Chere to Buy the &uel +ump and 4ave.

%ore /.-6 Jeep )iagnostic Tutorials.

!&:to&s o/ a ou?ll probably see one or more of the following symptoms1

5. ;ough idle.

2. *ngine starts after extended cranking.

. 6ack of power when accelerating the vehicle down the road.

/. Back"fires thru? the intake manifold when accelerating your pickup or van down theroad.

Both of these conditions can be tested with a fuel pressure gauge. lright, with this info under our

belts, let?s get testing.

TE!T 16>s'* !tart'* l5+ To Co'/r& La@ o/ 5el
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The P@uick and dirtyL way to check to see if a lack of fuel is causing your /.-6 Jeep to no start is using

starting fluid $although it?s not the most accurate way of diagnosing a bad fuel pump(.

The rule of thumb is that if by spraying starting fluid your Jeep starts, even if momentarily... then this

tells you that fuel is missing from the e@uation $engine start e@uation1 fuelsparkairQcombustion(.

OTE6To get an accurate test result from the starting fluid test, you need to first confirm that the

ignition coil pack is creating and delivering spark to all 9 cylinders. >ou can easily accomplish this by

attaching a spark tester to the spark plug wires and having a helper crank the engine $while you

observe to see if the spark tester sparks(.

#%PORT$T6This is a very fast and easy test but you do have to take one very important safety

precaution and this is to reconnect the air intake duct after spraying starting fluid down the throttle

bore $although you don?t have to fasten it(. This will prevent any backfire, that might occur, from

scaring the heck out of you when cranking the engine.

This is what you have to do1

1.1

Re&oe the 'ta@e ar +5t /ro& the throttle 3o+. >ou don?t have to

completely remove it, since you?ll have to reconnect it in one of the next steps.

2.2

O:e' the throttle :late a'+ s:ra start'* /l5+ +ow' the 3ore.

s a safety precaution reconnect the air duct after you have sprayed a good

s@uirt of starting fluid $but you don?t have to tighten the air duct?s hose clamp(.

3.3


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Cra'@ the e'*'eonce the air duct is back on and you?re clear of the engine

compartment.

4.4

Yo5,ll *et o'e o/ two res5lts wth ths test6

1.)The engine will start momentarily and after a few seconds will die or.

2.)The engine will only crank but not start at all.

OI, let?s find out what your results mean1

C$!E 16#/ the e'*'e starte+ a'+ ra' /or a /ew seo'+s1 This test result tells you that the no start

problem is due to a lack of fuel.

>our next step is to check to see what the fuel pressure is with a fuel pressure test gauge. Go to1

T*4T 21 0hecking &uel +ressure Cith a &uel +ressure Gauge.

C$!E 26The e'*'e ++ 'ot start? 'ot ee' &o&e'tarl1 This usually means that a lack of fuel '4


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Ce can connect a fuel pressure gauge to the fuel system using the 4chrader valve located on the

fuel in#ector rail $see photo above(.

OTE6'f you don?t have a fuel pressure gauge, take a look at the section1 Chere to Buy a &uel

+ressure Test Gauge.

OI, let?s get started with this test1

1.1

Plae a sho: towel aro5'+ the !hra+er ale. The shop towel?s #ob is to

absorb any fuel that may leak when doing step 2.

2.2

Co''et the /5el :ress5re *a5*eto the 4chrader valve on your /.-6 Jeep?s fuel

in#ector rail.

3.3

he' rea+? as@ o5r hel:er to le the @e o' a'+ o// 35t +o',t ra'@ the

e'*'ewhile you observe the fuel pressure tester?s gauge.

0heck the connection at the 4chrader valve for fuel leaks and if any tighten the

fuel pressure a bit more $by hand only( to eliminate them.

4.4

Yo5r /5el :ress5re *a5*e sho5l+ re*ster6 70 to 4 P!#with the Iey On

*ngine Off $IO*O( if the fuel pump is OI.

6et?s take a look at what your results mean1

C$!E 16#/ the /5el :ress5re *a5*e re*stere+ 0 P!#This confirms that the cause of your /.-6

engine?s no start problem is caused by a lack of fuel.


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How To Test The TP!(1997-199 4.0L Gra'+ Chero@ee)

%ay -, 2-5/>:+ate+6%ay 2=, 2-58rtte' 36braham Torres"rredondo$rtle #+6922

Page 1

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The throttle position sensor $T+4( on your 5=="5==8 Jeep Grand 0herokee can be accurately tested

with a simple multimeter to find out if it?s bad $or not(.

lso, you don?t have to remove it to test it and no scan tool is re@uired for the test. 'n this tutorial '?ll

show you #ust how.

3ere are the contents of this tutorial at a glance1

4ymptoms of a Bad Throttle +osition 4ensor $T+4(.

T*4T 51 Testing the T+4 7oltage 4ignal.

T*4T 21 7erifying T+4 3as +ower.

T*4T 1 7erifying T+4 3as Ground.

Chere to Buy >our T+ 4ensor and 4ave.

%ore Jeep /.-6 Test Tutorials.

To see the T+ sensor?s wiring diagram go to1 1997-199 TP !e'sor r'* "a*ra& (ee: Gra'+

Chero@ee 4.0L).
http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-3http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1#1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1#2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-2#2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-3http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-3#2http://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-wiring-diagramhttp://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-wiring-diagramhttp://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-3http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1#1http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-1#2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-2#2http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-3http://troubleshootmyvehicle.com/jeep/4.0L/tps-multimeter-test-3#2http://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-wiring-diagramhttp://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-wiring-diagram


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&or the T+4 on 5==9 and newer Grand 0herokee, go to1 How to Test TP! Co+es6 P0121? P0122?

P0127 (199-2001 ee: 4.0L).

!&:to&s o/ a our Jeep Grand 0herokee fails the state mandated emissions test.

/. Bad gas mileage.

8. 3ard start and!or extended cranking time $after shut off(.

9. Black smoke coming out of the tailpipe.

. 3esitation when accelerating your Jeep down the road.

TE!T 16Test'* the TP! ;olta*e !*'al

To get your T+4 diagnostic on its way, you first need to identify ORGI"= $orange w! dark blue

stripe( wire of the sensor?s wire connector.
http://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-tests-1http://troubleshootmyvehicle.com/jeep/4.0L/throttle-position-sensor-tests-1


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The ORGI"= wire is the middle wire of the connector and is the one that carries the throttle

angle voltage signal, the T+4 creates $and it?s the one we?re gonna? tap into with a multimeter(.

Chen the throttle position sensor $T+4( fails, it?ll fail in one of two ways. 't?ll either stop producing a

throttle angle signal.. which usually means it?ll stay stuck at a certain voltage value. Or the T+4 will

fail intermittently.

The test below will help you check for both types of failures.

OTE6To ensure the accuracy of your test, my suggestion is to test the throttle position sensor $T+4(

with a warmed up engine $but not running(.

OI, let?s start1

Part 1

1.1

+lace your multimeter in 7olts )0 mode and with the ;*) multimeter lead probe

the wire labeled with the '5&3er 2in the illustration above. This is the circuit that

supplies the T+ 4ignal to the +0%.

'f you don?t have a multimeter or need to upgrade yours, check out my

recommendation1be?s %ultimeter ;ecommendation$found at1

easa5to+a*'osts.o&(.

OTE6The throttle position sensor has to remain connected to its connector for

this test to work $this is where a wire piercing probe comes in handy to get to the

signal inside the wire. To see what one looks like, click here1 Cire +iercing +robe

Tool.(

2.2

Ground the B60I multimeter test lead on the battery negative terminal. 3ave

you helper turn the Iey On, but don?t start the engine $this will power up the T+

sensor(.

3.3

>our multimeter should report ./ to .= 7olts )0. 'f your multimeter doesn?t, don?t

worry about it #ust yet, continue with the other steps.

Part 2

1.4


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&or this test result to be accurate, you need to open the throttle by hand and not

from inside the vehicle.

2.5

s the throttle opens, the voltage numbers will increase. This increase in voltage

should be smooth and without any gaps or skips. Once the throttle is wide open,

your multimeter should read somewhere between .8 to /.8 7olts )0.

3.6


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... the T+4 may be missing either power or ground. 4o the next step is to check that the T+4 is

getting power, go to T*4T 21 7erifying T+4 3as +ower.

TE!T 26;er/'* TP! Has Power

The ;#OIHT$violet w! white stripe( wire is the one that feeds power $8 7olts )0( to the throttle

position sensor $T+4(.

This power comes from the +0%. 'n other words, the other end of the ;#OIHTwire connects

directly to your Jeep Grand 0herokee?s powertrain control module $+0%(.

The ;#OIHTwire is the one that connects to terminal N in the photo in the image viewer.

OTE6>ou can test for these 8 volts )0 with the T+ sensor connected or disconnected to the T+4. '

personally prefer to do this test with the T+ sensor?s connector unplugged.

This is what you?ll need to do1

1.1

+lace your multimeter?s dial in volts )0 mode.

2.2

+robe the '5&3er 7wire, with the ;*) multimeter lead and an appropriate tool

$like a Cire"+iercing +robe(. The throttle position sensor?s connector can be

connected to the sensor or not when you probe this circuit.

#%PORT$T'f you probe the front of the T+4 harness connector, be careful and

don?t damage the terminal. )amaging the terminal will re@uire that you replace

the connector.

3.3
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0onnect the B60I multimeter lead to a good and clean ground point on the

engine or directly on the negative $"( battery terminal.

4.4

Chen you?ve set up the test, have a helper turn the Iey On *ngine Off $IO*O(.

5.5

>our multimeter should display /.8 to 8 7olts on its screen. OI, now let?s interpret

your test results below1

C$!E 16%5lt&eter re*stere+ 4. to ;olts. 4o far so good since this tells you that the throttle

position sensor $T+4( is getting power from the powertrain control module $+0%(.

The next step $and the last test( is to check that the


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O'e6's not creating an appropriate throttle position signal $T*4T 5(.

Two6That the sensor is getting power in the form of 8 7olts from the ;#OIHTwire $T*4T 2(.

s mentioned earlier, the throttle position sensor $T+4( needs power and ground to create a throttle

angle voltage signal the +0% can use to find out how much you?re stepping on or off the accelerator

pedal. 'n this last test step, we?re gonna? check that the


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. The T+4 is being fed ground.

Therefore, you can conclude that the T+ 4ensor is B) and needs to be replaced $and that this will

solve the T+ sensor code lighting up the check engine light(.

C$!E 26%5lt&eter "#" OT show 11 to 12 ;olts. )ouble check that you?re testing the correct T+

sensor harness terminal wire and repeat the test. 'f your multimeter still doesn?t show the indicated

voltage...

...then this indicates a problem with either your Jeep?s +0% $internal fault!problem( or an open in the

wire between the T+4 harness connector and the +0%?s harness connector

lthough testing these two conditions are beyond the scope of this article, you have now eliminated

the throttle position sensor $T+4( on your Jeep as being the cause of the problem and!or the T+4

)iagnostic Trouble 0ode $)T0( lighting up the 0heck *ngine 6ight $0*6(. >ou can use the wiring

diagram found in the following article to check continuity of the T+ sensor circuits1

1997-199 TP !e'sor r'* "a*ra& (ee: Gra'+ Chero@ee 4.0L).

25-pin data link connector diagnosticsYou will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this

page.

Figure 1 - Connection Diagram
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Figure 2 - Connecting 'TEN' to 'GND'.

How to perform the testPlease note that this sequence is based on the 25-pin DLC fitted to Mazda variants as listed in the Fault

Code Table.

1.Plug oneBNC test leadintoChannel Aof theoscilloscope.

2.Connect aBack-pinning Probeto thecolored plugon theBNC test lead, and probe it into the 'B+'

terminal on the DLC socket.

3.Connect anotherBack-pinning Probeto theblack plugon theBNC test leadand probe it into the 'FEN'

terminal on the DLC Socket as shown inFigure 1.

4.Using a suitable piece of insulated wire, connect one end to the DLC socket into the 'TEN' terminal and

connect the other end to the 'GND' terminal.

5.Press the spacebar on the PC to start the scope displaying live data.

6.Switch on the vehicle ignition and follow the instructions below. The codes will then appear on the screen, as

shown below.

Accessing fault codes from the PCM memory

Once the scope has been correctly connected to the 25-pin DLC socket:

1.Switch the ignition on.

2.The codes will now be displayed on the screen. Once the first code is repeated, this indicates all codes havebeen read from the PCM.

3.Switch ignition off.

4.Analyze any codes retrieved from PCM.
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Erasing fault codes from the PCM memory

1.Ensure the ignition is switched off.

2.Disconnect the battery earth cable for at least 30 seconds.

3.Depress the brake pedal for at least 20 seconds (total 50 seconds).

4.Reconnect the battery earth cable.

5.Repeat the code reading sequence to ensure all DTCs have been removed from the memory of the PCM.

WARNING:Disconnecting the battery may erase the memory from ancillary devices such as clocks and radios.

Important Note:This sequence is for the Mazda variants listed in the Fault Code Table. For other manufacturers,

check if the vehicle is equipped with a 25-pin DLC connector and also check to see if the above test can be carried

out. Serious damage to the PCM will occur if the test is carried out on a vehicle that does not support the above test

method. Refer to the manufacturer's wiring and technical information for further support.

Example waeforms

Example waveform 1 - No fault codes present (P000)
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Example waveform 2 - Fault codes present (P0110)
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Exaqmple waveform 3 - Multiple fault codes present (P0100 - P0110 - P0120)

!aeform notes

How to interpret the codes from the example waeforms
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Figure 3 - How to read fault codes

The sequence begins with a long pulse, indicating the start of the code-reading sequence from the PCM. The

example waveforms show codes in the 4-digit EOBD/OBDII format, but other variants of Mazda give a two-digit code

flash sequence. Consult the manufacturer's technical information for two-digit codes.

The 4-digit code in Code Sequence 1 is indicated by 4 groups of signals.

"igit #

The first digit is a single, long pulse (indicated by a white arrow)

As there is no short pulse, the first digit is a 0.

"igit 2

Digit 2 consists of a long pulse (white arrow) followed by a short pulse (black arrow).

This pattern indicates that the second digit is a 1.
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"igit $

Digit 3 is again just a single long pulse, indicated by a white arrow.

This pattern indicates another 0.

"igit %

Digit 4 is also a single long pulse (indicated by another white arrow).

This digit is another 0.

Putting these four digits together gives Code 0100, which is the EOBD Code for "Mass Air Flow (MAF)

sensor/volume air flow (VAF) sensor circuit malfunction".

Example waeform #

There are no pulses after the start pulse, indicating that all digits are 0. The table below tells us that:

Code P0000= EOBD Code for No Fault Found.

Therefore there are no fault codes present on the vehicle.

Example waeform 2

There is one code that is repeated as it is the only code stored in the PCM. The table below tells us that:

Code P0110= EOBD Code for Intake Air Temperature (IAT) Sensor.

Example waeform $The PCM is signalling 3 codes. The table below tells us that:

Code P0100= EOBD Code for Mass Air Flow (MAF) sensor/volume air flow (VAF) sensor circuit malfunction.

Code P0110= EOBD Code for Intake Air Temperature (IAT) Sensor.

Code P0120= EOBD Code for Thottle Position (TP) sensor A/Accelerator pedal position (APP) sensor A circuit

malfunction.

&otes A long pulse followed by 2 short pulses indicates a '2', as shown in example waveform 3. Higher digits are

obtained by adding more short pulses.

Each 4-digit code is separated from the next by an 8-second delay to allow you to tell them apart.

If only one code is stored in the PCM, then this code will be continuously repeated as a single fault code.

If more than one code is stored in the PCM, all codes will be read and then repeated untill the sequence is

stopped.


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Figure 4 - Engine management control

'echnical informationThe engine management system is constantly monitored by the PCM as the engine is running under different loads

and conditions. All of the input and the output signals are monitored at all times. This is done so that the PCM can

keep control of the engine and maintain optimum running conditions at all times. The PCM checks the values from

the sensors and compares them with the information stored in the ROM (Read Only Memory) of the PCM. Based on

the information stored, the PCM changes the commands to the actuators to alter any parameters to keep optimum

running.

While the PCM is reading from ROM and reading all the signals from the sensors and actuators, thus monitoring the

operating parameters of the engine, it is also monitoring the tolerances and ranges of each sensor and actuator tosee if they are working correctly. When the PCM sees that a component or tolerance is breached then it will initiate a

DTC (Diagnostic Trouble Code) which is stored in the RAM section of the PCM, often known as KAM (Keep Alive

Memory), or in the EEPROM (Electronically Eraseable Programmable Read Only Memory). The DTC is then stored

until action is taken: the fault is rectified on a self-check system, or an instruction is sent to the PCM to clear the

DTC and the system is rechecked to ensure that it is operating correctly again.

There are a number of different methods for accessing fault codes depending on the system used on the vehicle -

EOBD, OBD I or OBD II:

Using the MIL Light on the Dashboard to flash the code in a given sequence.

Connecting a LED, test lamp or scope to a DLC connector and observing the long and short flashes

(pulses).

Connecting a scan tool to the DLC connector and communicating with the PCM directly.
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()"-* +(n-)oard "iagnostics *,

This legislation requires that vehicles manufactured from 1988 onwards be equipped with a system that is controlled

electronically by a computer and is capable of monitoring itself during operation. Any malfunction in the system that

leads to an effect in the exhaust emissions has to illuminate a warning light on the dashboard and present a stored

DTC. The DTC must accessible and readable with the use of on-board facilities such as Flash Code, LED, Test

Lamp, Oscilloscope.

()"-**The legislation that supports OBD-II applies to vehicles that are manufactured from 1994 onwards (Spark Ignition

Engines) and 1996 onwards (Compression Ignition Engines). The main features fitted and that have to be monitored

constantly are as follows:

Internal Combustion

Catalytic Converter

Levels of Oxygen (Oxygen Sensors)

Secondary Air System

Fuel Evaporative Control

EGR (Exhaust Gas Recirculation)

The key features for DTCs are as follows:

1.The Malfunction Indicator Lamp (MIL) has to be provided for warning the driver that a fault is present with anadditional flashing function.

2.The DTCs must be read from the PCM using a scan tool through the 16-Pin DLC Connector

3.All emission-related components have to be monitored by the PCM for the operation of the engine as well as

monitoring the components for defects.

4.When a fault occurs, the system has to be capable of logging perfomance data in the form of a freeze frame.

5.The codes must be formatted to a universal format so that all scan tools and diagnostic equipment can read

them and the user can easily interpret them. SeeFigure 5.

CODE PART POSSIBLE ARRANGEMENT MEANING

1 B BODY Control Code

1 C CHASSIS Control Code

1 P POWERTRAIN Control Code OBD II

1 U UNDEFINED - Used for Network Systems, CAN Bus

2 0 Fault Code given under the SAE testing guidelines

2 1 Fault Code given under the Manufacturer's guidelines


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CODE PART POSSIBLE ARRANGEMENT MEANING

2 2 Fault Code given under the Manufacturer's guidelines

2 3 Reverse Fault Code

3 1 Fuel and Air Measurement System

3 2 Fuel and Air Measurement System

3 3 Ignition System

3 4 Exhaust Control System

3 5 Engine Speed and Idling Control System

3 6 PCM, Computer Control & Output Signals

3 7 Transmission Control Systems

4 01 to 99 Assignment of System Components

Figure 5 - Structure of Standard Fault Codes

%ass $r low !e'sor Re&oal? Clea''* J #'stallato'$ or $ %ss'* E'*'e

%any owners have experienced DboggingD or DmissingD or #ust unsteady performance in their /.-engine and have been frustrated by lots of expensive Dnon"fixesD. fter riding on a plane next to a

manufacturing trainer from a company that builds O*% replacement auto electrical components forplaces like utoRone and 0arEuest, Jack 6obdell tried his tip. The trainer says that &ord has theseproblems more than other makes and the /.- engine seems to be more susceptible to the problemthan other &ord engines.

't seems that a DmissingD engine culprit is actually the computer?s sensor inside the %ass ir &low4ensor $%&(. 't eventually #ust gets a little dirty or builds up its own patina in the filament wires. dirty or slightly patinated filament will send the wrong air reading to the computer, saying it is gettingmore air than it really is and the computer will tell the *&' to send in the wrong mix of fuel, thus, thebogging. The patina seems to form faster if you live in a damp climate. Jack 6obdell lives in


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engine. >ou should have solved any bogging or missing problems. Jack?s flat idle spot is ancienthistory.

>ou?ll need to remove these Torx head screws $(

This is what you?ll be cleaning $B(


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T"2- Torx Bit This is a 0;0 electric contact typecleaner #ust for %&?s with a +etroleum

)istillate!lcohol base

ote6)O


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Re&oal6

Ca5to' -The mass air flow sensor hot wire sensing element and housing are calibrated as a unitand must be serviced as a complete assembly. )o not damage the sensing element or possiblefailure of the sensor may occur.

5( )isconnect the negative battery cable.


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To remove the %& sensor, first disconnect the wire harness plug ...

... then remove the air cleaner"to"throttle body air tube

2( )isengage the wiring harness connector from the %& sensor, and if necessary, the 'T sensor.

( 6oosen the engine air cleaner outlet tube clamps, then remove the tube from the engine.

/( ;emove the %& sensor from the air cleaner assembly by disengaging the retaining clips.


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;emove the four %& sensor attaching screws ...

... then remove the sensor from the air cleaner housing

#'stallato'6

5( 'nstall the %& sensor to the air cleaner assembly and ensure that the retaining clips are fullyengaged.

2( 'nstall the air cleaner outlet tube, then tighten the outlet tube clamps until snug.

( ttach the engine wiring harness connectors to the 'T and %& sensors.

/( 0onnect the negative battery cable.

ote6

"rt %$ Ca5s'* :'* 5'+er loa+ -%y 5==/ /.- idled fine, but a dirty %& was the cause of aping under load. this page had led me to believe that if my idle was okay then the %& was not aproblem, hence it took me a long time to get to the %& after messing with a bunch of other stuff.


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*nough people say that the %& was the source of their ping that maybe a little re"phrasing on thispage would make it a little more clear. *ric 4teinberg

>:+ate - This page was updated 52!2-- to replace the use of carburetor cleaner with electricalcleaner.

Procedures for the Automotive Oxygen Sensor

Testing

Click to Get Book Here...

By Mandy Concepcion

TheO2 sensor measuresthe oxygen

content of the exhaust. The O2 sensors

sensing ability comes about by

producing a small voltage proportionate

to the exhaust oxygen content. In other

words, if the oxygen content is low it

produces a high voltage (0.90 Volts -

Rich mixture) and if the oxygen content

is high it produces a low voltage (0.10

Volts - Lean mixture). Although

theoretically the O2 sensor should cycle

between 0.00 volts and 1.00 volts, inreality it cycles between 0.10 volts and 0.90 volts.

A GMO2 sensorsignal stuck at 450 mV is an indication of an open O2 sensor circuit (signal wire) or

faulty O2 signal ground. The 450 mV value (GM) is called a bias voltage and it is not the same for all

manufacturers. Some manufacturers employ a dedicated O2 sensor ground. Such a ground lead is

attached to the engine block or chassis and feeds an ECM O2 ground pin only. The O2 circuit is then

grounded through the inside of the ECM electronic board by this ground wire. A loss of this ground

would also put the O2 sensor signal at around 450 mV, which also makes it look like an open circuit.

The same holds true for Chrysler, but these use a different O2 bias voltage, which is usually 2.00 to4.00 volts.

1) A few key issues are very important in the analysis of O2 sensor signals.

2) AnO2 sensorwill cycle between 0.10 to 0.90 or almost 1 volt.

3) An O2 sensor has to reach the 0.8x Volts amplitude mark while at full operation.

4) An O2 sensor also has to reach the 0.1x Volts amplitude mark while at full operation.

5) Full operation means the engine is fully warmed up, O2 sensor above the 600 deg. F. operating

temperature, and no fuel or mechanical problems present.

6) The O2 sensor must cycle at least once per second, which would show 3 cross counts on the scantool PID.

7) Silicone is the leading cause of O2 contamination.

8) It is easier for an O2 sensor to go from rich to lean than vise-versa.

9) O2 sensors tend to fail on rich bias. In other words, they tend to shift their cycling to the upper side

or rich side of the voltage scale.
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10) Contrary to what many people think, an O2 sensor WILL NOT cycle by itself. The O2 sensor cycle

is a direct result of the ECM response to the changes in the mixture.

11) Any time the O2 cycles and crosses the 0.450 volts mark, the system is in CLOSE-LOOP.

12) Even though an O2 sensor is cycling and crossing 0.450 volts (ECM in close loop) it DOES NOT

mean that it is working properly.

13) O2 sensor operation is extremely important not only to keep HC & CO emissions low but also to

the NOx as well.

14) Proper O2 sensor cycling will determine the catalytic converters efficiency. The catalytic

converter needs the O2 sensor cycling at its proper amplitude and frequency for it to function at its

maximum efficiency.

15) An O2 sensor with a high voltage reading does not necessarily mean that the mixture is rich or

high in fuel content. An EGR valve problem will send the O2 signal high as well.

A big misconception among technicians trying to understand O2 sensors is that they cycle by

themselves. The O2 sensor just reads oxygen content in the exhaust, THATS IT. Excess oxygen in

the form of regular ambient air will send the O2 sensor voltage signal low (under 0.450 volts) and lack

of it will send the voltage signal high (over 0.450 volts). A stuck open EGR valve will create a lack ofoxygen in the exhaust, since the re-circulating exhaust has all its oxygen already burnt . The ECM

sometimes uses the O2 sensor to check for proper EGR operation and sets a code if necessary. So,

be aware of the fact that a vehicle might be running lean because the ECM sees a rich O2 signal due

to a defective (stuck open) EGR valve. Since the ECM sees a rich signal, it will try to correct with a

lean command and try to lower theO2 sensorshigh voltage signal.

CONDITION THAT AFFECT OPERATION

NOTE: WHEN PERFORMING O2 SENSOR CHECKS, IT IS IMPORTANT TO TAKE MEASUREMENTS AT IDLE AND 2000 RPM. BE

AWARE THAT O2 SENSOR PRE-CONDITIONING IS IMPORTANT, EVEN ON THE NEWER STYLED HEATED O2 SENSORS. PRE-

CONDITION THE O2 SENSOR BY RAISING THE ENGINE SPEED TO 2000 RPM FOR ABOUT 15 SECONDS OR SO. THE O2

SENSOR HAS TO BE ABOVE 600 F. TO BE ABLE TO OPERATE PROPERLY. LONG PERIODS OF IDLE TIME CAN RENDER A

NON-HEATED OR OLDER O2 SENSOR TOO COLD FOR IT TO FUNCTION AT ALL. AT THE SAME TIME, DO NOT TRY TO

FORCE A HEATED O2 SENSOR INTO OPERATION. AN O2 SENSOR WITH A FAULTY HEATER WILL GO INTO CLOSED-LOOP

AFTER A GOOD WARM-UP SESSION.
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After an engine has ran through its warm up period (O2 sensor has no effect on engine operation

while the engine is cold), the ECM then looks for the O2 value. The 0.450 volts mark is considered

almost universally as the midway point or crossover point for O2 sensor operation. If the signal is on

the rich side (above 0.45 volts), then the ECM will answer with a lean command (reducing injector

pulsation), or if the signal is on the lean side (below 0.45 volts) then the ECM will answer with a rich

command (increasing injector pulsation). The amount of injector pulse correction is proportional to the

voltage seen by the ECM at the O2 sensor signal wire. The higher the voltage the more the ECM

reduces on-time to the injector. The lower the voltage the more the ECM increases the injector on-

time. The ECM is constantly doing exactly just that, slightly increasing and decreasing injector

pulsation. The constant adjustment is what gives the O2 sensor signal the switching appearance

(sine wave) on the scope screen.

NOTE: The ECMs fuel pulse corrections performed constantly to the injector signal is called SHORT

TERM FUEL TRIM ( GM called it INTEGRATOR ) and LONG TERM FUEL TRIM ( GM called it

BLOCK LEARN ) on the scanner. FUEL TRIMS is the systems deviation of the BASE-INJECTION

pulse. Analyzing LTFT and STFT is a great way to know a particular vehicles fuel consumption trend

or how well that vehicle has been performing with regards to fuel control. STFT and LTFT is the firstthing to look for when assessing fuel control problems.

The fact that the O2 sensor signal is switching rich-lean-rich-lean also reveals that the ECM is

controlling the injector pulsation and therefore that the system is in close loop mode. An ECM in full

control (O2 sensor cycling) is said to be in close loop because of the close-circuit action of O2

sensor-to ECM-to injector pulse control then to O2 sensor and back to the ECM. The ECM must be in

control at all times except during warm up, WOT, power enrichment, and deceleration mode.

The O2 sensor not only has to cycle, it also has to cycle fast enough (proper frequency) and wide

enough (proper amplitude). At least one cycle per second ( 1 Hz ) must be seen at the signal wire in

order for the O2 to be considered good (not lazy). A one cycle per second will make the scope trace

go across the 0.450 volts mark approximately 3 times, which the ECM recognizes as 3 cross counts.

A slow O2 sensor will have a damaging effect on the catalytic converter and release excessive

amounts of emissions to the atmosphere.

A cycle are the complete rich and lean crests of the O2 sensor signal, while crossing the 0.45 voltage

point. Proper amplitude refers to the O2 sensors ability to reach full rich ( 0.90 volts ) and full lean

( 0.10 volts ) when cycling. The higher the voltage seen at the O2 signal line the more the ECM

reduces pulsation to the injectors. The lower the voltage seen at the O2 signal line the more the ECMincreases injector pulsation. This is the reason why an O2 sensor that is not reading the mixture

properly, at full amplitude and frequency, will actually misguide the ECM into a wrong fuel control

pattern. Once the O2 sensor has reached its correct temperature of 600 F, look for an O2 signal

cycle with the correct amplitude and frequency and it will surely indicate a perfectly operating O2

sensor.

COMPONENT TESTING

(click play button to show video)

NOTE: On early OBD II systems, the post catalytic converter O2 sensor has no effect on fuel control.

The post catalytic O2 sensor was originally responsible for only monitoring catalytic converter

efficiency. On most systems, the post converter O2 sensor signal should never mimic or follow the

pre-cat O2 signal. That would indicate a defective or low oxygen storage capability at the converter .
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On early OBD II systems, the post-cat O2 sensor should show little or no voltage fluctuations on a

scope waveform, since all the mixture fluctuations are being absorbed by the catalytic converter.

Stating around model year 1999, a new type of converter came on the market, called Low Oxygen

Storage Converter or LOC. With an LOC, the pre and post O2 sensors cycle at the same rate. These

converters are tested by measuring the lag-time between the two signals. A further development of

this system is that the post converter signal is also used for A/F correction, but to a less extent.

These simple steps should be followed whenever testing O2 sensors.

Scan the vehicle for any O2 sensor codes and analyze the data stream PID. O2 sensor voltage should cycle normally

with proper amplitude and frequency. An O2 sensor stuck at a fixed bias voltage is an indication of an open O2 circuit

or lack of O2 sensor (dedicated) ground. If possible use a graphing multi-meter to analyze the O2 sensor data to

determine any possible problems.

While reading the scan values, goose the throttle and observe for O2 sensor minimum and maximum values (0.1x volts

to 0.9x volts). Although this is not a conclusive evidence of correct O2 sensor operation, it serves as a preliminary

indication of proper operation.

Some automotive manufacturers employ a dedicated O2 sensor ground wire that is grounded somewhere at the engine

block or chassis. A loss or rupture of this ground wire will render the O2 sensor useless. This ground wire feeds only

the ECMs O2 sensor circuit. The main engine ground does not feed this type of O2 sensor circuit.

Verify the O2 sensor wire integrity. Most O2 sensors are biased and an open signal wire will give a reading of whatever

the bias voltage is. Later model Jeep/Chrysler O2 circuits tend to be biased at around 2 or 4 volts, therefore, a constant

reading of around 2 or 4 volts on a Chrysler is also an indication of an open circuit. In many of these cases, the ECM

will put an O2 sensor High Voltage code.

Finally, verify for correct O2 sensor operation with a scope or graphing multi-meter. Check for proper amplitude and

frequency. Remember that the scanner O2 sensor readings are only interpreted values and may not show the real

voltage reading. This is the reason for doing this final manual test.

OXYGE !E!OR "#$GO!#!

O2 sensors are amazingly rugged considering the operating environment they live in. But O2 sensorsdo wear out and eventually have to be replaced.

The performance of the O2 sensor tends to diminish with age as contaminants accumulate on thesensor tip and gradually reduce its ability to produce voltage. This kind of deterioration can be causedby a variety of substances that find their way into the exhaust such as lead, silicone, sulfur, oil ashand even some fuel additives. The sensor can also be damaged by environmental factors such aswater, splash from road salt, oil and dirt.

s the sensor ages and becomes sluggish, the time it takes to react to changes in the air!fuel mixtureslows down which causes emissions to go up. This happens because the flip"flopping of the fuelmixture is slowed down which reduce

how to test the rear o2 heater

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