O2 Sensor Signal Stuck Rich (Bank 1, Sensor 1)
The upstream oxygen sensor on bank 1 returns a constant rich signal under deceleration fuel cut-off where lean is expected. Often a contaminated sensor (silicone, oil, coolant) or short to ground that pulls the signal high in some sensor types.
Affected components
- Oxygen sensor upstream
Common causes
- High likelihood: Upstream sensor contaminated
- Medium likelihood: Upstream sensor failed stuck rich
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.