What P0131 means
The upstream oxygen sensor is reporting a persistently low voltage, indicating a lean condition or a failed sensor.
Common causes
- Exhaust leak ahead of the sensor
- Vacuum leak
- Failed sensor
- Low fuel pressure
How it is usually fixed
- 1Smoke-test for intake and exhaust leaks
- 2Check fuel trims
- 3Replace the sensor if the circuit tests good
Other common codes
- P0011 — Camshaft Position A – Timing Over-Advanced (Bank 1)
- P0030 — HO2S Heater Control Circuit (Bank 1, Sensor 1)
- P0101 — Mass Air Flow Circuit Range/Performance
- P0113 — Intake Air Temperature Sensor Circuit High
- P0118 — Engine Coolant Temperature Sensor Circuit High
- P0138 — O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)
Code information is general guidance, not a diagnosis for a specific vehicle. Confirm with live data and manufacturer test procedures before replacing parts.