Catalyst System Efficiency Below Threshold (Bank 1)
Powertrain Code · Medium
What does P0420 mean?
The catalytic converter on bank 1 is not operating efficiently. The downstream O2 sensor readings indicate the catalyst is not converting exhaust gases properly. May need catalyst replacement or could be caused by a failed O2 sensor.
System: Catalytic Converter
P0420 is a powertrain diagnostic trouble code indicating catalyst system efficiency below threshold (bank 1). This code is classified as medium severity, which means: schedule service — affects performance or emissions. We have vehicle-specific diagnostic data for 50 models below. Select your vehicle for tailored causes, symptoms, and repair cost estimates.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your vehicle.
See causes, symptoms, and repair costs for P0420 on specific vehicles: