P0131
O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
Oxygen sensor (fuel & air)
Generic OBD-II
Medium
What it means
P0131 means the upstream oxygen sensor on bank 1 (sensor 1) is reporting a persistently low voltage. That can mean the sensor or its wiring is faulty, or the exhaust is genuinely running lean. The ECM relies on this sensor to trim the air/fuel mixture, so the main effects are poorer fuel economy and higher emissions — the engine still runs and starts normally.
Medium
Can I keep driving? Yes — the car will run and start, but expect worse fuel economy and it will fail an emissions test until repaired.
Common symptoms
What you'll notice
- Check-engine light on
- Poor fuel economy
- Slight hesitation or rough running
- Failed emissions/smog test
Common causes
Most likely first
- Faulty upstream O2 sensor (bank 1, sensor 1)Likely
- Signal wire shorted to ground or open in the O2 circuitCommon
- Exhaust leak ahead of the sensor skewing the readingCommon
- Genuine lean condition (vacuum leak or low fuel pressure)Less often
- Failed ECM/PCM (rare)Less often
How to diagnose & fix
Work through it in order
- View the bank 1 sensor 1 O2 voltage and fuel trims in live data to see whether the reading is stuck low or the engine is truly lean.
- Inspect the O2 sensor wiring and connector for damage or a short to ground.
- Check for exhaust leaks near the sensor and vacuum leaks that could cause a lean condition.
- Confirm fuel pressure is in spec if trims show a real lean condition.
- Replace the O2 sensor if it's faulty. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0131?+
Yes, short-term. The engine runs, but the ECM is working with a bad oxygen-sensor signal, so fueling and economy suffer. Fix it before an emissions test and to avoid wasting fuel.
Can I just clear P0131?+
It returns within a drive cycle or two unless the sensor, wiring, or underlying lean condition is repaired.
Related codes
Often seen with P0131
Read & clear P0131 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX