P0151 fault code: O2 Sensor Circuit Low Voltage

P0151 means “O2 Sensor Circuit Low Voltage” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. A scan can confirm P0151; do not clean the MAF because bank 2 looks lean.

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 P0151

Do not drive. The upstream oxygen probe on bank 2 is reporting voltage the computer treats as too low. Mixture control on that second bank may go open-loop or biased; this is not a MAF-clean tutorial.

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 P0151 and any companion codes
  • O2 Sensor Circuit Low Voltage: Whether the engine management light is steady or flashing
  • O2 Sensor Circuit Low Voltage: Any P0174-class lean code on bank 2 stored with this low-voltage flag
P01xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0151 mean?

P0151 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 P0151 fail an MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off.

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.
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P0151 — quick answers

Is it safe to drive with P0151?

Do not drive. We have no verified driving guidance for low voltage on the bank-2 upstream oxygen circuit. Escalate driving to stop-until-checked. Do not spray cleaner into the intake for this code.

Will P0151 fail my MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off.

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.