EmissionsSeverity Medium: diagnose soon
P0131O2 Sensor Circuit Low Voltage (bank 1 sensor 1)
What it means
The oxygen sensor bank 1 sensor 1 stays at a low voltage (lean reading) for too long. The upstream sensor (before the catalyst) is what the ECU uses to correct the mixture.
Symptoms
- Check engine light
- Higher fuel consumption
- Possibly a rough idle or failed emissions test
Common causes
- Real lean condition (vacuum leak, low fuel pressure)
- Exhaust leak upstream of the sensor drawing in air
- Signal wire shorted to ground
- Failed sensor
What to check first
- Check fuel trims: if they are high, look for the cause of the lean mixture first
- Propane-enrich the intake: a good sensor goes above 0.8 V
- Check for exhaust leaks and the sensor wiring
Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.