The downstream Bank 1 sensor signal is stuck lean — a sensor or exhaust condition. Often no drivability change.
SYMPTOMS
- Check-engine light
LIKELY CAUSES
- Failed rear O2 sensor
- Exhaust leak
- Rarely a cat or fuel issue
DIAGNOSIS STEPS
- View rear O2 live data
- Inspect exhaust for leaks
- Replace sensor
RELATED PARTS
- Downstream O2 sensor