P0420
Catalyst system efficiency below threshold (Bank 1)
The engine control system has detected that catalyst efficiency on Bank 1 is below the expected threshold.
What this code means
The engine control system has detected that catalyst efficiency on Bank 1 is below the expected threshold.
Possible causes
- Aging or damaged catalytic converter
- Downstream oxygen-sensor problem
- Exhaust leak
- Fuel or combustion problem affecting catalyst performance
Common symptoms
- Check-engine light
- Often little or no noticeable drivability change
- Possible emissions-test failure
Checks to make
- Scan for other stored engine codes first
- Check for misfire or fuel-mixture faults
- Inspect for exhaust leaks
- Compare upstream and downstream oxygen-sensor behaviour with suitable diagnostic equipment before condemning the catalyst
Safety
- Exhaust components can become extremely hot. Allow the exhaust to cool before inspection and use appropriate lifting/support equipment if working underneath the vehicle.
Model notes
P0420 does not by itself prove that the catalytic converter must be replaced.