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p0420 code

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28K views 7 replies 6 participants last post by  guy7bmwm5  
Check your book for warranty, I don't think it is only Ca anymore, could be a long federal one on Cats too.

The easiest way to diagnose a bad cat is to run it at a high idle when warmed up, look at the O2s with a scan tool. The front (sensor 1) should pulse up and down in voltage, the rear (sensor 2) should stay steady at around .3 or .4 IIRC, steady for sure anyway. If the rear follows the front up and down the cat isn't working.

Again double check the warranty in the book, look for emissions and/or cat converter warranty, don't trust the dealer to tell you. Cats are expensive.