Getting P0420 Code Repeatedly – What Else Should I Check After Replacing the Catalytic Converter?
Quote from WrenchWizard on July 15, 2025, 10:13 amHey everyone,
I’ve been dealing with a persistent P0420 code (Catalyst System Efficiency Below Threshold – Bank 1) on my 2012 Toyota Camry. I already replaced the catalytic converter and both upstream and downstream O2 sensors about 2 months ago, but the check engine light came back on recently, and the same P0420 code is showing up again.I’ve checked for exhaust leaks and didn’t find any noticeable issues. The engine seems to run fine, fuel economy is okay, and there are no strange noises or smells.
Could it be an ECU issue? Or should I be looking at something like the rear O2 sensor wiring or maybe the air-fuel ratio sensor?
I’d really appreciate any insights or ideas on what else to check or reset. Anyone else experienced something similar after replacing the converter?
Thanks in advance!
Hey everyone,
I’ve been dealing with a persistent P0420 code (Catalyst System Efficiency Below Threshold – Bank 1) on my 2012 Toyota Camry. I already replaced the catalytic converter and both upstream and downstream O2 sensors about 2 months ago, but the check engine light came back on recently, and the same P0420 code is showing up again.
I’ve checked for exhaust leaks and didn’t find any noticeable issues. The engine seems to run fine, fuel economy is okay, and there are no strange noises or smells.
Could it be an ECU issue? Or should I be looking at something like the rear O2 sensor wiring or maybe the air-fuel ratio sensor?
I’d really appreciate any insights or ideas on what else to check or reset. Anyone else experienced something similar after replacing the converter?
Thanks in advance!