Question about 2002 Pontiac Grand Prix

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Service engine light,code po 420

I purchased the 2002 Gran Prix,runs great,but service engine light came on.I scanned it and code PO420 engine catalyst showed up,it has a replacement convertor on it,probably aftermarket.I replaced the rear O2 sensor,it looked burnt.The light returns after a couple days driving.I talked to GM dealer they stated it must be a cheap convertor,but cannot warranty,because it is not original.I need to know if a walker replacement convertor will solve the problem or does it have to be GM.Thanks for any information.

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  • aceg238 Feb 19, 2009

    I am going to try a walker direct fit convertor,will let you know results in a week or two.



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A good brand name direct fit converter should keep the light off as long as the cause of the first converter failure is corrected. I would not use a universal fit one. Walker is a good brand, I have used them and never had a problem. Here is some more information, hope this helps.

When diagnosing a PCM code or codes: P0420, P0430, be sure to determine the cause of the converter failure. These converters are not likely to fail without an external cause. Typical causes are: fuel pressure regulator leak, engine misfire, dirty fuel injectors, coolant consumption, etc. Also, be aware that some converters on the market will cause this code or codes due to a lack of oxygen storage capacity. A component that must be in these converters, Cerium, is required to store, then slowly release oxygen. NOTE: P0420 is a bank 1 converter code, P0430 is a bank 2 converter code. If the vehicle has only one converter, then P0430 does not apply.

Posted on Feb 19, 2009


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There's a new answer to your Jeep 2008 Patriot question! Author image Bogdan Odwazny wrote: The code is po420? This was your reply to my first question some time ago. The answer is YES the c

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Catalytic Converter System, Bank 1 - Efficiency Below Threshold
Possible Causes:
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- Check Oxygen Sensor(s).
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- Perform Oxygen Sensor(s) Aging Check.
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I’m happy to assist further over the phone at

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