Question about 1998 Chevrolet Cavalier

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1998 Chevrolet Cavalier 0420 Code

I keep getting a 0420 code. The entire exhaust, to include the cat and both 02 sensors have been replaced. I cannot find any advanced troubleshooting procedures for this code. Anyone have any ideas?

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  • mew2149 Jun 04, 2009

    Sorry it has taken so long to post my results, but you are right on the money! The cat I put on the vehicle initially was the cheapest one I could find. Bad move .... Replaced it with a quality one and bingo ... the light went out in three drive cycles (I refused to reset it again) and it is running like a top. I compared both cats once I got the initial replacement off and was amazed at the difference. The cheap on was lighter and looking through it the gaps in the honey comb were at least twice as large as those in the quality one. Once installed, the quality one even changed the sound of the exhaust a little. OH ... difference in price between the quality one and the cheap one was about 30 bucks ... my labor/diagnostics time/ect .... well, more than the cost of the cat for sure!!!!

    Thank you!!

  • Anonymous Mar 21, 2014

    I replaced both 02 sensors and the cat and now have a 21 code
    and a27code

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Here is something from a reference guide that we follow at my shop, hope it helps.

When diagnosing a PCM code PO420, be sure to determine the cause of the converter failure. 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.

Posted on Mar 10, 2009

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