P0131
PowertrainOxygen Sensormoderate severityO2 Sensor Circuit Low Voltage Bank 1 Sensor 1
What P0131 Means
The upstream O2 sensor voltage on Bank 1 is staying below 0.45V, indicating a lean condition or sensor fault.
Symptoms
- Check Engine Light
- Lean running
- Poor fuel economy
- Rough idle
Common Causes
- Vacuum leak
- Faulty O2 sensor
- Exhaust leak before sensor
- Low fuel pressure
- Faulty fuel injector
Diagnostic Steps
- Check for vacuum leaks
- Monitor O2 sensor voltage
- Test fuel pressure
- Perform smoke test on intake
- Inspect O2 sensor
Where to start: Fix vacuum or exhaust leak. Replace O2 sensor if confirmed faulty.
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