O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
The downstream oxygen sensor signal is fixed at a low voltage. Either the catalyst is letting unburned oxygen through (sensor sees lean), the sensor itself is shorted to ground, or the catalyst is so degraded that the downstream signal mirrors a lean upstream condition.
Affected components
- Oxygen sensor downstream
- Catalytic converter
Common causes
- Medium likelihood: Signal wire shorted to ground
- Medium likelihood: Catalyst degraded (often appears before P0420)
- Low likelihood: Exhaust leak between catalyst and downstream sensor
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.