O2 Sensor Signal Stuck Lean (Bank 1, Sensor 1)
The upstream oxygen sensor on bank 1 returns a constant lean signal during conditions where rich content is expected (for example after a deceleration fuel cut-off recovery). Usually a sensor that has lost its rich-side response or a slow heater warm-up.
Affected components
- Oxygen sensor upstream
- Oxygen sensor heater
Common causes
- High likelihood: Upstream sensor failed stuck lean
- Medium likelihood: Sensor heater slow to warm up
Possible symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.