P0131
Moderate severityOxygen (O2) Sensor Circuit Low Voltage (Bank 1, Sensor 1)
Drivable, but the upstream O2 sensor controls fuel mixture. Bad data hurts fuel economy and emissions. Check within a week.
Stop driving if: the check engine light is flashing, or the car starts running noticeably worse
What does the P0131 code mean?
The P0131 code means the upstream oxygen (O2) sensor on Bank 1 is reading a voltage that’s too low for too long. The upstream O2 sensor sits in the exhaust before the catalytic converter and tells the computer how much oxygen is in the exhaust, so it can adjust fuel delivery.
A low reading can mean either the sensor is faulty or the engine is genuinely running lean. P0131 often appears with P0171 when there’s a real lean condition.
Can you keep driving with a P0131 code?
Yes, with care. The engine still runs, but fuel economy and emissions will be off. If you also have a lean code like P0171, fix the lean cause first – it may be what’s setting P0131 too.
What causes a P0131 code?
Listed in the order most shops would check them — cheapest and most likely first, not as statistical odds. The real cause varies by year, make, model and engine.
- Wiring or connector issueCheck 1st
- Exhaust leak before the sensorCheck 2nd
- Lean condition (vacuum leak, low fuel pressure)Check 3rd
- Faulty O2 sensorCheck last
How to diagnose a P0131 (check these first)
- Scan for P0171 — if present, fix the lean cause first.
- Inspect the O2 sensor connector for damage or corrosion.
- Look for exhaust leaks between the engine and the upstream O2 sensor.
- Test fuel pressure; replace the O2 sensor if everything else checks out.
P0131 repair cost
Typical US ranges including parts and labor (varies by vehicle):
Costs vary a lot by vehicle and region. These are typical US ranges including parts and labor — treat them as a ballpark for the conversation with your shop, not a quote.
| Oxygen (O2) sensor | – 0 |
| Exhaust leak repair | 0 – 0 |
| Vacuum leak repair | – 0 |
Tools & parts that help
A scanner confirms P0131 and any companion lean codes – so you fix the real cause, not just swap an O2 sensor that wasn’t the problem.
See top-rated OBD-II scanners ›As an Amazon Associate I earn from qualifying purchases. This costs you nothing extra and never changes what we recommend.
P0131 — Frequently asked questions
Is it safe to drive with a P0131 code?
Yes, with care. The engine runs, but fuel economy suffers. Fix it within a week.
What does Bank 1 Sensor 1 mean?
Bank 1 is the side of the engine with cylinder 1. Sensor 1 is the upstream O2 sensor (before the catalytic converter).
Can a vacuum leak cause P0131?
Yes. A vacuum leak makes the engine run lean, which the O2 sensor reports as low voltage – sometimes triggering P0131.
How much does it cost to fix a P0131?
-0 for a new O2 sensor, or less if the cause is an exhaust or vacuum leak.
Related codes
General guidance based on the standard SAE definition of the P0131 code. A real diagnosis depends on your make, model, year, engine and other symptoms. This is not a substitute for a professional inspection — when in doubt, have a technician confirm the cause before replacing expensive parts.