P0142 fault code: O2 Sensor Circuit

P0142 means “O2 Sensor Circuit” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. Confirm P0142; locating a rare third bank-1 probe 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 P0142

Do not drive. A third oxygen sensor on bank 1 (sensor 3, only on some exhaust layouts) has a circuit fault. Not every car fits this extra probe; the code still names that circuit, not a generic emissions pack.

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: Registration number
  • O2 Sensor Circuit: Exact code P0142 and any companion codes
  • O2 Sensor Circuit: Whether the engine management light is steady or flashing
  • O2 Sensor Circuit: Engine layout (inline or V) and how many oxygen sensors the garage can see from above
P01xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0142 mean?

P0142 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”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0142 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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P0142 — quick answers

Is it safe to drive with P0142?

Do not drive. We have no verified driving guidance for bank-1 sensor-3 oxygen-circuit trouble. Escalate to do-not-drive until a garage maps whether your exhaust actually uses a third probe on bank 1.

Will P0142 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.