O2 Sensor Signal Stuck Lean (Bank 1, Sensor 2)
The downstream oxygen sensor on bank 1 reports a constant lean signal during a forced-rich command from the ECU. Suggests either a sensor that has lost its rich-side response, or a catalyst that is so degraded that no rich exhaust reaches the downstream sensor (cross-check P0420).
Affected components
- Oxygen sensor downstream
- Catalytic converter
Common causes
- High likelihood: Downstream sensor failed stuck lean
- Medium likelihood: Exhaust leak after catalyst
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.