O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
The upstream oxygen sensor signal is fixed at a low voltage, indicating the ECU sees a continuously lean exhaust on bank 1 — or the sensor signal path is shorted to ground.
Affected components
- Oxygen sensor upstream
- Exhaust pipe pre cat
Common causes
- High likelihood: Exhaust leak upstream of the sensor
- Medium likelihood: Signal wire shorted to ground
- Medium likelihood: Genuine lean running (vacuum leak, low fuel pressure)
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.