P0131O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The oxygen sensor before the catalytic converter on bank 1 (sensor 1) is the main control sensor for the mixture. It is either a switching sensor (about 0.1 V lean to 0.9 V rich) or a wide-band sensor that works with a pump current evaluated by an interface chip. On switching sensors it means the signal stays below about 40–60 mV (GM, two trips; some GM engines also require the downstream sensor to read rich at the same time, since a genuinely lean mixture would show there too). On wide-band sensors (Ford from 2011, GM) it has nothing to do with the mixture: the interface chip reports one of the sensor wires shorted to ground. A really lean mixture leads to P0171/P2195 rather than this code. A stored code usually switches mixture control to open loop and suspends adaptation and converter monitoring.
- What you may notice
- Check engine light on
- Higher consumption, possibly rough running (no mixture control)
- Higher emissions, possible emissions test failure
- Possibly with P0171/P2195
- Likely causes
- LikelySignal wire (or a wide-band sensor wire) shorted to ground, e.g. chafed on exhaust or gearbox
- LikelySensor faulty or poisoned (permanently lean signal)
- PossibleLarge exhaust leak ahead of the sensor or misfires
- PossibleConnector wet or corroded
- RareControl module or interface chip faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.