The Bank 1 catalytic converter is no longer converting efficiently (the rear O2 trace mirrors the front).
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 that killed the cat
DIAGNOSIS STEPS
- Confirm there are 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