Quote:
Originally Posted by Twalif10M535
The code im getting is P0420. Catalyst system efficiency below threshold bank1
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I would still suspect the upstream O2 sensor (you didn't say what year your car is or the mileage, that matters). I had that same code on my last car and it was the O2 sensor.
https://www.obd-codes.com/p0420
https://www.fixdapp.com/blog/p0420-code