P0131 fault code: O2 Sensor Circuit Low Voltage

P0131 means “O2 Sensor Circuit Low Voltage” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. You may confirm P0131 on a scanner; do not replace the upstream oxygen sensor yourself.

Do not DIYReviewed page boundary
ToolsSpecialist equipment

This is the conservative boundary from the reviewed code record. This page has no frozen site-wide safety grade, so it does not publish a repair route.

What to tell the garage about P0131

Stop driving now. The computer sees too low a voltage on an oxygen-sensor circuit. On usual OBD numbering P0131 is bank 1 sensor 1, before the catalyst. We have no verified drive rating — do not assume it is safe to keep driving.

Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.

  • O2 Sensor Circuit Low Voltage: Registration number
  • O2 Sensor Circuit Low Voltage: Exact code P0131 and any companion codes
  • O2 Sensor Circuit Low Voltage: Whether the engine management light is steady or flashing
  • O2 Sensor Circuit Low Voltage: Upstream (bank 1 sensor 1) voltage or AFR reading if the scanner showed it
  • O2 Sensor Circuit Low Voltage: Any petrol smell, black smoke, or rough idle you noticed
Hot systems

Never open a hot coolant cap — pressure can scald you. Exhaust and catalytic converter get hot enough to burn and ignite debris. Stay clear of electric fans; they can run after shut-off.

P01xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0131 mean?

P0131 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P01xx block, which covers fuel and air metering. The stored description is “O2 Sensor Circuit Low Voltage”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0131 fail an MOT?

If the engine management light is on with P0131 stored, that illuminated lamp is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. Emissions may also fail if fuelling is wrong.

Before booking your test, check what usually fails on your car: see our MOT pass rates by make and model, built from 33.1 million DVSA tests.

Related guides

Car diagnostic test cost: compare the scopeUK booking marketplaces currently publish diagnostic averages of about £52–£65. Engine management light on: steady or flashing?A steady engine management light means the computer has stored a fault. Drive with caution and get the code read. A flashing light is different — stop when it is safe.
P0100Mass or Volume Air Flow Circuit P0101Mass or Volume Air Flow Circuit Range/Performance P0102Mass or Volume Air Flow Circuit Low Input P0103Mass or Volume Air Flow Circuit High Input P0104Mass or Volume Air Flow Circuit Intermittent P0105Manifold Absolute Pressure/Barometric Pressure Circuit P0106Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance P0107Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

P0131 — quick answers

Is it safe to drive with P0131?

Stop driving now. Driveability guidance is not available for P0131 — treat as do not drive until checked. A low upstream oxygen-sensor voltage is a fuelling-signal fault; if the engine runs rich, smells of fuel, or the light flashes, stop and arrange recovery.

Will P0131 fail my MOT?

If the engine management light is on with P0131 stored, that illuminated lamp is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. Emissions may also fail if fuelling is wrong.

Fault-code identifiers are standard diagnostic facts. Their explanations and diagnostic guidance on this site are original editorial summaries, not reproduced SAE wording. MOT defect rules reflect the DVSA MOT inspection manual (2026). This page is general guidance for UK drivers, not a substitute for a professional diagnosis.