P0131 — O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
Drive with caution — fix soon.
What P0131 means
P0131 means the front (upstream) oxygen sensor on Bank 1 is sending a voltage that's too low, which the computer reads as a constantly lean exhaust. The cause might be the sensor itself, its wiring, or a real lean condition such as an air or vacuum leak. Because this sensor directly guides fuel delivery, fixing it restores smoother running and proper emissions.
Common symptoms
- Check engine light on
- Reduced fuel economy
- Rough or unstable idle
- Hesitation or slight loss of power
- Possible failed emissions test
Common causes
- Failed upstream oxygen sensor (Bank 1, Sensor 1)
- Damaged or corroded sensor wiring or connector
- Vacuum or intake air leak causing a true lean condition
- Low fuel pressure or a weak fuel pump
- Exhaust leak near the sensor letting in outside air
- Faulty mass airflow (MAF) sensor
Typical repair cost
$150 – $450
Varies by vehicle and root cause.
Frequently asked questions
Can I drive with a P0131 code?
Yes, short-term driving is usually fine, though you might feel a rough idle or use a bit more fuel. Address it soon so a lean condition doesn't damage the catalytic converter.
How much does it cost to fix P0131?
Replacing the oxygen sensor typically costs $150-$450 including labor. If the cause is a vacuum leak or wiring, the price can vary depending on the repair.
Is P0131 serious?
It's moderate. The car stays drivable, but a persistent lean signal can hurt fuel economy and, over time, the catalytic converter.
Could a vacuum leak cause P0131 instead of a bad sensor?
Yes. An intake or vacuum leak adds extra air and creates a genuinely lean mixture, so a technician should check for leaks before simply replacing the sensor.