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Question:

Help with my 2002 Chevy Impala with engine light ?

3.4 and with in 2 months the cat coverter was replaced twice. Then the o2 sen replaced then things fine for day then engine light was back on. took car back in the tested and keeps bringing back to cat converter. So what else can I be looking to check?

Answer:

You dont make it come back. The check engine light comes on when a sensor notices a problem. If the problem is not there, the system will NOT triger a check engine light. Another words, if the light is out, let it be. When the light comes on again, you can trace the cause of the problem then.
We have been seeing a lot of failures of the original converters in these cars, and GM has even been replacing them for free under special policy #05551, up to 10 years and 120,000 miles, but the new converters are redesigned - they do not typically fail. This does not explain why you have had to replace several of them. Typically when the catalytic converter fails repeatedly it is caused by an engine misfire condition. When a misfire occurs, unburned gasoline in the exhaust stream burns inside the converter, overheating it and causing it to fail. I suspect that this is what is happening. In other words, you need to find the reason why the converter is failing repeatedly. Some more information would help. There are several ways that catalytic converters can fail. Some questions: Has your service engine light ever been flashing, or was it always on steady? If the light flashes it means that the computer has detected a misfire, which as I stated before can damage the converter. How does the vehicle run? Does it seem to have enough power? Does it seem like the transmission is shifting in a way that you are not used to? (A misfire or other engine performance problem often shows up as late or harsh transmission shifting.) Are we just talking about the light being on with no running problems? Finally, are these GM original equipment converters or something from Autozone or Napa? I'm not trying to slam aftermarket parts, I have a very specific reason for asking this question. It has to do with the fact that you said you replaced one of the oxygen sensors. I won't go any farther with this aspect just yet, but I need to know this. It would be helpful if you could tell me if your car has ever set a diagnostic code P0420. Get back to me and I'll try and help. Mike

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