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2003 Pontiac Vibe P0420 Code: Cat Converter Issue After O2 Sensor Replacement

Model: Pontiac Vibe Fault Code: P0420 Posted: 2017-12-09 17:52

I recently replaced the catalytic converter and post-catalyst oxygen sensor on my 2003 Pontiac Vibe. The new gasket was installed, and I confirmed that both components were properly secured. However, the vehicle is now showing a P0420 diagnostic code. There's no visible smoke or unusual odors, and the car runs normally. I'm concerned whether this code indicates a deeper issue with the catalytic converter efficiency or if it might be related to a previous seal failure or fuel system contamination.

Related fault codes

P0420

Comments (2)

Anonymous 2017-12-09 22:53

Did you replace both the catalytic converter and the post-catalyst oxygen sensor? Was the P0420 code present before or after these part replacements?

Anonymous 2017-12-11 22:32

No, neither the catalytic converter nor the post-cat O2 sensor were replaced. I'm fairly confident the original issue wasn't caused by a faulty seal or clogged cat. My gas tank had a hole, so I used Catastatic to clean it. The check engine light has turned off on its own after 200 miles of driving—so far, this seems promising. Still, I'd like to confirm if the P0420 code could be linked to fuel system contamination or converter performance.