Same as P0420 for Bank 2 — the catalyst is no longer converting efficiently.
SYMPTOMS
- Check-engine light
- Possible mild economy loss
- Failed emissions
- Often no drivability change
LIKELY CAUSES
- Aged or failed catalyst
- Exhaust leak
- Faulty downstream O2 sensor
- Upstream misfire/oil contamination
DIAGNOSIS STEPS
- Confirm no misfire or lean codes first
- Compare front vs rear O2 traces
- Inspect for exhaust leaks
- Test or replace the catalyst
RELATED PARTS
- Catalytic converter
- O2 sensors