The post-catalyst (rear) O2 sensor on Bank 1 reports a persistently lean condition that fuel trim cannot correct.
SYMPTOMS
- Check-engine light
- Mild economy loss
- Possible rough idle/hesitation
LIKELY CAUSES
- Exhaust leak ahead of the rear sensor
- Failing downstream O2 sensor
- Fuel delivery issue
- Intake leak
DIAGNOSIS STEPS
- Inspect exhaust for leaks
- Check downstream O2 data
- Verify fuel pressure and trims
RELATED PARTS
- Rear O2 sensor
- Exhaust gaskets