P0131 — 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.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Oxygen sensor upstream
- Exhaust pipe pre cat
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Exhaust leak upstream of the sensor
- Signal wire shorted to ground
- 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
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
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.