P0157 fault code: O2 Sensor Circuit Low Voltage

P0157 means “O2 Sensor Circuit Low Voltage” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. Confirm P0157; do not raise the car to chase a low rear-probe reading.

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 P0157

Do not drive. The downstream oxygen probe on bank 2 is reporting voltage treated as too low. A grounded-looking rear probe on bank 2 is a circuit reading, not proof that bank’s brick is spent.

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 P0157 and any companion codes
  • O2 Sensor Circuit Low Voltage: Whether the engine management light is steady or flashing
  • O2 Sensor Circuit Low Voltage: Whether water or salt corrosion is visible on rear connectors from the side (no crawl)
P01xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0157 mean?

P0157 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 P0157 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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P0157 — quick answers

Is it safe to drive with P0157?

Do not drive. We have no verified driving guidance for low voltage on bank-2 rear oxygen. Escalate: stop until a garage confirms. Do not jack the car to reach the after-cat probe.

Will P0157 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.