Fault in the upstream (pre-cat) Bank 1 lambda sensor circuit or signal.
SYMPTOMS
- Check-engine light
- Poor economy
- Rough running
- Failed emissions
LIKELY CAUSES
- Failed O2 sensor
- Wiring/connector fault
- Exhaust leak
- Contamination (oil/coolant/silicone)
DIAGNOSIS STEPS
- View sensor live data
- Check heater circuit and wiring
- Inspect for exhaust leaks
- Replace sensor
RELATED PARTS
- Upstream O2 (lambda) sensor