P0161 fault code: O2 Sensor Heater Circuit

P0161 means “O2 Sensor Heater Circuit” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. A reader can show P0161; bank-2 rear heater repair is professional 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 P0161

Do not drive. The heater circuit for the downstream oxygen probe on bank 2 is out of range. That heater only warms the rear bank-2 probe; it is not a fuel-trim or misfire diagnosis.

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 P0161 and any companion codes
  • O2 Sensor Heater Circuit: Whether the engine management light is steady or flashing
  • O2 Sensor Heater Circuit: Whether the code set on a cold start, when heaters normally draw current
P01xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0161 mean?

P0161 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 P0161 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

P0161 — quick answers

Is it safe to drive with P0161?

Do not drive. We have no verified driving guidance for a bank-2 rear oxygen-heater circuit. Some neighbouring heater codes are graded; those ratings are not reused here. Stop until a garage checks the heater supply.

Will P0161 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.