P0155 fault code: O2 Sensor Heater Circuit

P0155 means “O2 Sensor Heater Circuit” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. You may confirm P0155 on a scanner; heater-circuit repair and sensor replacement are garage work.

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 P0155

Do not drive. The heater for the bank-2 upstream oxygen sensor is not working as the computer expects. This is a heater-circuit fault on the bank that does not contain cylinder 1, not a mixture or catalyst verdict.

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 Heater Circuit: Registration number
  • O2 Sensor Heater Circuit: Exact code P0155 and any other oxygen-sensor or heater codes
  • O2 Sensor Heater Circuit: Whether Bank 1 heater codes were also stored
  • O2 Sensor Heater Circuit: Whether the engine management light is steady or flashing
  • O2 Sensor Heater Circuit: Any live-data notes for Bank 2 Sensor 1 if the scanner showed them
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 P0155 mean?

P0155 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 Heater Circuit”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0155 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.
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

P0155 — quick answers

Is it safe to drive with P0155?

Do not drive. Driveability guidance is not available for this code — treat as do not drive until checked. Do not assume P0155 is as mild as a Bank 1 heater code.

Will P0155 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.