Question about 1996 Isuzu Trooper

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Check engine light due to Catalytic converter

Had a diagnostic check on my 1996 Isuzu Trooper after the check engine light came on. was due to a catalytic converter. still running smoothly & was told it would probably take a while to affect anything. I wanna fix it now regardless. any way to attempt to clear the problem without replacement? thanks Ramon fromTN

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  • ram0njr May 19, 2009

    for clarification, this 96 trooper has a 3.2 engine & 162,000 miles. not sure about the diagnostic code but it came up Catalytic converter when prompted by the tech. it is manual transmission. not sure if this made a difference but i treated the fuel system with slick 50 high mileage fuel treatment & the check engine light came on after driving 40 miles or so after the treatment. 
    thanks. Ramon from TN

  • ram0njr May 22, 2009

    thanks for the info. i had the previous owner of the trooper send me his maintenance records & he had the catalytic converter replaced in '06. so i will try changing the spark plugs per your suggestion & see what happens. thanks again for the advice.
    ram0n from TN   

  • Dave  C
    Dave C May 11, 2010

    What was the code number, engine size, mileage?



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Without knowing the specific code, I will assume it relates to an inefficient catalytic converter. At this mileage it could very well mean that the catalytic converter is failing to do it's job and needs to be replaced. The computer sets this code when it sees a signal from the rear O2 sensor start to change in time with the front O2 sensor. It should not. If the cat is working, The rear O2 sensor should have a stable output as the cat is supposed to be removing all the oxygen from the exhaust. Sometimes this code will set if the spark plugs or the engine's state of tune has deteriorated and is producing more emission than the cat can handle, the rear O2 sees the overflow and assumes the cat is bad.
At your present mileage, I would strongly suggest changing the spark plugs if they have not been done in the last 20,000 mi. Have the light reset and drive it to see if the code returns. If it does, replace the catalytic converter. I suspect that you do need a cat, but I view the spark plugs as maintenance, and I wouldn't want to put a brand new cat in without the assurance that my old plugs were not going to damage the new one.
Hope this helps,

Posted on May 19, 2009


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Catalytic converter is clogged or out of medium.

Replace it.


Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.


* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem

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