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Re: dtc error code po420
This can be a complicated diagnosis, p0420 is a comparison of the pre cat sensor and the post cat sensor and how the pcm interpets these inputs, there are several comprehensive tech articles on this, you could google that code or check batauto.com and do a search for that code much has been discussed. Or do what Bnaylor says, didn't see his post, but the info is out there for the diagnostic issue in question.
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