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Old 02-15-2014, 01:05 PM   #1
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Join Date: Feb 2014
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Location: Rutland, VT
What I Drive: 2003 ZX3

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Diagnosing P0420 ?

I recently acquired a 2003 ZX3 with 143,000 miles on it. It has a few little problems and I've been learning a lot reading threads on the forum. All of the problems seem to be pretty common and I'm real pleased to have such a great resource as these forums.

I've been reading about the P0420 code and these vehicles. Some have suggested that misfires can throw the code, but my vehicle runs very smoothly without misfiring.

Others have suggested that the catalytic converters rarely go in these vehicles. I've also seen suggestions that the original computers were flashed with too sensitive a trip for this code and perhaps I should have the computer re-flashed.

I have not seen (might have missed it) a straightforward diagnostic approach to figuring out what to do next to diagnose this code.

Looking forward to suggestions. Thanks.

Last edited by PaulK1970; 02-15-2014 at 01:11 PM. Reason: Mistake in Code #
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