P0131 Oxygen sensor circuit low voltage (bank 1, sensor 1)
What P0131 means
The upstream oxygen sensor on bank 1 is reporting a voltage that stays too low, which normally means the exhaust looks lean. The engine computer cannot use it to control fuelling properly. On many modern cars this is a wide-band (air-fuel ratio) sensor, but the meaning of the code is the same.
P0131 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- Medium
- Typical repair cost
- 60–350 €
- Workshop time
- 0.5–3 h
- Repair difficulty
- Medium
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Higher fuel consumption
- Possible hesitation or rough idle
- Failed emissions test
Common causes
- Worn or contaminated upstream oxygen sensor
- Exhaust leak before the sensor drawing in outside air
- Genuinely lean mixture from a vacuum leak or low fuel pressure
- Signal wire shorted to ground
Can I keep driving with P0131?
You can keep driving, but have it checked within a week or two. The engine may use more fuel, and a long-standing upstream sensor fault can eventually harm the catalytic converter.
What to check first
- Check fuel trims in live data: high positive trims suggest a real lean condition rather than a sensor fault.
- Look for exhaust leaks at the manifold gasket and front pipe ahead of the sensor.
- Inspect the sensor wiring for chafing or a short to ground.
- If no leak or lean condition is found, replace the upstream oxygen sensor.
Related codes
- P0130 Oxygen sensor circuit (bank 1, sensor 1)
- P0132 Oxygen sensor circuit high voltage (bank 1, sensor 1)
- P0133 Oxygen sensor slow response (bank 1 sensor 1)
- P0134 Oxygen sensor circuit no activity detected (bank 1, sensor 1)
- P0135 Oxygen sensor heater circuit (bank 1, sensor 1)
- P0136 Oxygen sensor circuit (bank 1, sensor 2)
- P0137 Oxygen sensor circuit low voltage (bank 1, sensor 2)
- P0138 Oxygen sensor circuit high voltage (bank 1, sensor 2)
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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