1994 Jeep Cherokee Jeep Code 21

MARKUSK11

MEMBER
1994 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
124,000 MILES

I have an ongoing propblem wit an error code 21 for my 94 jeep cherokee country. I have replaced the o2 sensor 3 times replaced relays cleaned contacts and it still perisits. Does anyone have a clue as to what to do or look for. I'm stumped.

Saturday, September 20th, 2008 AT 10:42 AM

5 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Are you using OEM parts?

02S shorted to voltage check the wiring all the way back to the computer

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Sunday, September 21st, 2008 AT 4:06 AM

MARKUSK11

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3 POSTS

Yes I am using a Bosch PN15704 O2 sensor. What should the voltage reading be?
I have checked for a short with an ohmeter and there is no short. This is a heated O2 sensor can there be a problem there? I have checked the reesistance cold and it is 3 to 4 ohms and hot the resistance is 6 to 7 ohms is this correct? I am using a haynes manual and it gives very little info.

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Sunday, September 21st, 2008 AT 11:38 AM

RASMATAZ

MECHANIC
75,992 POSTS

Check the voltage to it-I don't have the resistances specs-the voltage should be .45volts if its switching properly from lean to rich and vice versus-

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Sunday, September 21st, 2008 AT 1:01 PM

MARKUSK11

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3 POSTS

OK so what should I do if the input viltage is too high. Is that a bad ECM? Is it another problem? I don't get a lean or rich condition.

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Sunday, September 21st, 2008 AT 2:50 PM

RASMATAZ

MECHANIC
75,992 POSTS

You look for what's causing it to go lean such as below

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)