P0131 means O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1). The upstream oxygen sensor on bank 1 is reading lower voltage than expected for too long, which the computer reads as a constantly lean exhaust or a sensor fault. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0131 means
Oxygen sensors measure the oxygen left in the exhaust. Sensor 1 sits before the catalytic converter and is used for fuel control; sensor 2 sits after it and mainly monitors the converter. Most sensors have a heater so they start working soon after a cold start. A traditional zirconia sensor switches between about 0.1 volt (lean) and 0.9 volt (rich); many newer upstream sensors are wide-band air-fuel sensors that report differently, so check which type your engine uses.
P0131 symptoms
- Check engine light
- Rough running or hesitation on some vehicles
- Poor fuel economy
Common causes of P0131
- Exhaust leak ahead of the sensor drawing in air
- Real lean condition from a vacuum leak or low fuel pressure
- Failed sensor
- Wiring shorted to ground
How to diagnose P0131
- Check fuel trims to see whether the engine is really lean
- Inspect the exhaust manifold and joints ahead of the sensor for leaks
- Check the sensor wiring for chafing on the exhaust
- Watch the sensor signal respond to a brief snap of the throttle
Can you drive with P0131?
Usually yes, but fueling may be off; repair soon.
P0131 tips
Most P0131 codes on an engine that runs well come from an exhaust leak just ahead of the sensor or chafed wiring touching the exhaust. If fuel trims are also high, fix the lean condition first and the sensor code often goes away.
Will P0131 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0131 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0133 | O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) |
| P0134 | O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1) |
| P0171 | System Too Lean (Bank 1) |
| P0135 | O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) |
Guides that help
When it is more than a sensor
Oxygen sensor codes are fixed with a sensor, wiring, a fuse or an exhaust leak repair. An engine burning oil or coolant contaminates sensors quickly; if new sensors keep failing, check for blue or white exhaust smoke and a head gasket leak, and compare engines by code on our engines page if the engine is worn out.
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