Parts
$30–200
P0131 — O2 Sensor Low Voltage (Bank 1, Sensor 1)
CAUTIONIs it safe to drive? The upstream oxygen/air-fuel sensor is reading stuck-lean or has a circuit fault. Driveable but fueling suffers.
What P0131 means
The front O2/AFR sensor on Bank 1 is reading low (lean) or its circuit is faulty. This sensor is how the computer fine-tunes the mixture in real time.
Most likely causes (in order)
- Failed or contaminated O2/AFR sensor
- Exhaust leak before the sensor (pulls in outside air)
- Actual lean condition (vacuum/fuel)
- Sensor wiring / connector
Symptoms you might notice
- Check-engine light
- Rough running / poor economy
What to check first
Confirm it's the sensor vs a real lean condition: check fuel trims and look for an exhaust leak upstream of the sensor before replacing it.
Repair cost & difficulty
Labor
0.5–1.5 hr
Difficulty
DIY-friendly