P0131Powertrain
Powertrain · SAE
O2 Sensor 1 (Bank 1) — Low Voltage
Meaning
The voltage of the upstream oxygen sensor (bank 1, sensor 1) stays too low. The ECU reads the signal as a constantly lean mixture or as a sensor circuit fault.
Common causes
- Faulty or contaminated upstream O2 sensor
- Short to ground in the sensor wiring
- Genuinely lean mixture (air leak, low fuel pressure)
- Corroded connector or intermittent contact
- Exhaust leak ahead of the sensor
Symptoms
- Check engine light on
- Increased fuel consumption
- Rough idle and hesitation
- Possible smell of unburnt fuel
Severity
Moderate: the engine runs but with a non-optimal mixture; consumption and emissions rise and the catalytic converter may suffer over time.
What to do
- Read live sensor data and compare it with the downstream sensor
- Check sensor wiring and connector for shorts to ground
- Check fuel pressure and intake air leaks
- Replace the sensor if its signal stays low with correct fuelling