The upstream Bank 1 O2 sensor signal is biased/stuck lean.
SYMPTOMS
- Check-engine light
- Drivability/economy issues
LIKELY CAUSES
- Failing O2 sensor
- Exhaust leak
- Lean fuel condition
DIAGNOSIS STEPS
- View O2 live data
- Inspect exhaust for leaks
- Verify fuel trims
- Replace sensor
RELATED PARTS
- Upstream O2 sensor