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Po420 code

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Old 05-09-2009, 02:18 PM   #1
jprichard [OP] jprichard is offline
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Po420 code

Hey guys, got the 420 code (Catalysr efficiency below threshod bank 1.
I replaced rear Cat, checked for leaks before rear o2 sensor, ran injector cleaner. Cleared the code but still comes back. Any ideas? Rear o2 sensor? Thanks.
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Old 05-25-2009, 04:32 PM   #2
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Front O2

I would say the front O2. If both O2's are switching from rich to lean it is because the rear O2 is trying to correct the front O2. Replace the front O2.
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