OBD codes / P0131
P0131
ModerateO2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
P0131 is generally safe to drive with for a while — it mainly affects fuel trim and emissions, not whether the car runs. Still, get it diagnosed before replacing the sensor, since an exhaust leak or a real lean condition can mimic a bad sensor, and you don't want to pay for a part that wasn't the problem.
What this code means
Sensor 1 on Bank 1 is the upstream oxygen sensor — it sits before the catalytic converter and tells the computer whether the exhaust is running rich or lean so fueling can be trimmed. P0131 means that sensor's signal is stuck low (reading lean) longer than it should. The sensor itself is the most common cause, as they wear out over time, but an actual lean condition, an exhaust leak near the sensor that lets in outside air, or a wiring/connector fault can all produce it. It is worth confirming the cause, because a genuinely lean engine and a simply worn-out sensor set the same code.
Symptoms you might notice
- Check-engine light, often with no obvious drivability change
- Slightly reduced fuel economy
- Occasional rough running or hesitation
- Failed emissions test
What it costs to fix
Typical range: $150–$550 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Upstream oxygen (O2) sensor | $50–$250 | ~0.3–1 hrs |
| Exhaust leak repair near the sensor | $20–$200 | ~0.5–2 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
An oxygen sensor is the typical fix and is usually a low-hundreds job. A seized sensor that fights removal, or a sensor buried under heat shielding, adds labor. Genuine OEM sensors on some makes cost noticeably more than aftermarket.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0131 for my exact vehicle →
Frequently asked
Can I drive with P0131?
Usually yes, short-term — it mostly affects fuel trim and emissions rather than drivability. Get it diagnosed reasonably soon, both to restore fuel economy and because it will fail an emissions test.
Is P0131 always a bad O2 sensor?
No. The sensor is the most common cause, but an exhaust leak that draws in fresh air near the sensor, a wiring fault, or an actual lean fuel condition can all read the same way. Confirm before replacing the sensor.
How much does it cost to fix P0131?
Most often a low-hundreds repair if it's the oxygen sensor. It can rise if the sensor is seized or hard to reach, or if the real cause turns out to be an exhaust leak that needs welding or a new gasket.
What is the difference between P0131 and P0171?
P0131 is the upstream oxygen sensor reading low (lean) on its circuit; P0171 is the computer reporting the fuel system is actually running too lean. They can appear together — a real lean condition can drive both — which is why diagnosis looks at the whole fuel picture, not just the sensor.
Seeing P0131 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0131 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.