P0131
O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
The engine computer is seeing a very low signal from the front oxygen sensor on bank 1. This usually means the engine may be running too lean, or the sensor, wiring, or connector has a problem. It can cause rough running, higher fuel use, and emissions issues.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20–$250
- SHOP
- $120–$600
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Vacuum leak or unmetered air entering the engine
- Faulty upstream oxygen sensor (Bank 1 Sensor 1)
- Exhaust leak before or near the front oxygen sensor
Typical repair cost
DIY usually runs $20–$250. Typical shop repair lands around $120–$600, depending on the root cause.
01 / Definition
P0131 indicates the powertrain control module has detected a persistently low voltage signal from the upstream oxygen sensor on Bank 1, Sensor 1. This sensor is used for fuel control, so a low reading can be caused by a true lean exhaust condition, an exhaust leak, vacuum leak, fuel delivery problem, or a faulty sensor/circuit. The code sets when the signal stays below the expected range for too long under the right operating conditions.
02 / Drive status
With caution. You may be able to drive short distances, but the engine can run poorly and fuel economy may suffer. Do not ignore it, because a lean condition can damage the engine or catalytic converter if the problem is severe.
03 / Symptoms
- Check Engine Light on
- Rough idle
- Hesitation or stumble on acceleration
- Poor fuel economy
- Engine may feel weak or run lean
- Possible hard starting when cold
- Failed emissions test
04 / Causes
| 1 | Vacuum leak or unmetered air entering the engine | high |
|---|---|---|
| 2 | Faulty upstream oxygen sensor (Bank 1 Sensor 1) | high |
| 3 | Exhaust leak before or near the front oxygen sensor | medium |
| 4 | Wiring damage, corrosion, or loose connector at the oxygen sensor | medium |
| 5 | Low fuel pressure, restricted fuel filter, or failing fuel pump | medium |
| 6 | Mass air flow sensor or intake air measurement issue | low |
| 7 | Engine mechanical problem causing lean running | low |
05 / Diagnostic sequence
- 01Check for other codes first, especially lean codes, misfire codes, fuel trim codes, or MAF-related codes.
- 02Inspect the Bank 1 Sensor 1 oxygen sensor wiring and connector for heat damage, corrosion, looseness, or broken wires.
- 03Look for vacuum leaks at hoses, intake tubing, PCV system, brake booster hose, and intake manifold gasket areas.
- 04Check for exhaust leaks before the front oxygen sensor, including manifold cracks, gasket leaks, and loose fasteners.
- 05Review live data for fuel trims and oxygen sensor switching. Large positive fuel trims usually point to a lean condition.
- 06Test fuel pressure and fuel delivery if fuel trims are high or the engine shows lean symptoms.
- 07Verify MAF sensor operation and intake system integrity if no other cause is found.
- 08If wiring, leaks, and fuel delivery are normal, test or replace the upstream oxygen sensor.
06 / Repairs
| 1 | Repair vacuum leaks, intake leaks, or cracked hoses | $10–$200 |
|---|---|---|
| 2 | Repair exhaust leaks near the exhaust manifold or front oxygen sensor | $50–$400 |
| 3 | Clean or repair oxygen sensor wiring and connectors | $0–$100 |
| 4 | Replace the Bank 1 Sensor 1 oxygen sensor if it is slow, biased low, or failed | $50–$250 |
| 5 | Repair fuel delivery problems such as low fuel pressure, clogged filter, or weak pump | $100–$600 |
| 6 | Fix MAF or other engine management issues if tests point to incorrect air measurement | $80–$400 |
07 / Related codes
08 / FAQ
What does P0131 mean on a car?
It means the upstream oxygen sensor on Bank 1 is showing a voltage that is too low, or the engine is actually running too lean.
Can a bad oxygen sensor cause P0131?
Yes. A failing front oxygen sensor is a common cause, but vacuum leaks and fuel problems are also common.
Will P0131 make the car run poorly?
It can. The engine computer may not control fuel mixture correctly, which can cause rough idle, hesitation, and poor fuel economy.
Is P0131 the same as Bank 1 Sensor 1?
Yes. P0131 refers to the upstream oxygen sensor on Bank 1, also called Sensor 1.
Can I clear P0131 without fixing it?
You can clear it, but it will usually come back if the underlying problem is still there.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.