P0131 Code: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
🟠 Moderate severity · drivable
Drivable, but the engine may run lean and rough. Fix it soon for proper fuel control.
What P0131 means
The bank 1 upstream oxygen sensor is reporting very low voltage, which the computer reads as a lean mixture. This can be a genuinely lean engine or a sensor/circuit problem.
Symptoms
- Check engine light is on
- Rough running or hesitation
- Poor fuel economy
- Possible failed emissions test
Common causes
- most common: Vacuum leak causing a genuine lean condition
- common: Exhaust leak before the sensor
- common: Faulty upstream oxygen sensor
- less common: Shorted or damaged sensor wiring
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Find and repair vacuum leaks | Yes | $10–100 |
| Repair an exhaust leak near the sensor | Mechanic | $50–200 |
| Replace the bank 1 upstream oxygen sensor | Yes | $60–200 |
Frequently asked questions
Can I drive with a P0131 code?
Yes, but the engine may run lean and rough. Fix it soon.
What is the most common cause of P0131?
A vacuum leak causing a genuine lean condition, or a faulty oxygen sensor.
How much does it cost to fix a P0131?
$10–$100 for a vacuum leak, or $60–$200 for a new oxygen sensor.
Related codes
P0132
P0132 Code: O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)
P0133P0133 Code: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
P0171P0171 Code: System Too Lean (Bank 1)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.