P0420
Catalyst System Efficiency Below Threshold (Bank 1)
OBD-II
Catalytic converter
What it means
The catalytic converter is not cleaning the exhaust as well as it should. Before condemning the converter, rule out a failing downstream O2 sensor and exhaust leaks — those are far cheaper and mimic this code. Will fail an emissions test.
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P0421
Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Catalytic converterMedium
P0422
Main Catalyst Efficiency Below Threshold (Bank 1)
Catalytic converterMedium
P0430
Catalyst System Efficiency Below Threshold (Bank 2)
Catalytic converterMedium
P0431
Warm Up Catalyst Efficiency Below Threshold (Bank 2)
Catalytic converterMedium
P0432
Main Catalyst Efficiency Below Threshold (Bank 2)
Catalytic converterMedium
General reference only — what a code means can vary by make and model. Confirm with a qualified technician.