P0318 fault code: Rough Road Sensor 'A' Signal Circuit

P0318 means “Rough Road Sensor 'A' Signal Circuit” — an ignition system and misfire fault in the powertrain.

Can I DIY?

Professional-only boundary. No verified DIY checks for the P0318 circuit. Confirm the code and book a garage.

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 P0318

Do not drive. Rough-road sensor A circuit is faulty. The computer uses that signal to avoid false misfire counts on bumpy roads. It is not itself a misfire repair.

Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.

  • Rough Road Sensor 'A' Signal Circuit: Registration number
  • Rough Road Sensor 'A' Signal Circuit: Exact code P0318 and any companion rough-road or misfire codes
  • Rough Road Sensor 'A' Signal Circuit: Whether the engine management light is on
  • Rough Road Sensor 'A' Signal Circuit: Whether ABS or traction lamps are also on
P03xxIgnition system and misfire
MOT fail riskif the warning light stays on

What does P0318 mean?

P0318 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P03xx block, which covers ignition system and misfire. The stored description is “Rough Road Sensor 'A' Signal Circuit”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0318 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. Flashing engine management light and juddering: stop and recoverNo — do not continue the journey. A flashing engine management light with the car juddering is a stop-driving situation: ease off only enough to reach the nearest place of relat…
P0300Random/Multiple Cylinder Misfire Detected P0301Cylinder 1 Misfire Detected P0302Cylinder 2 Misfire Detected P0303Cylinder 3 Misfire Detected P0304Cylinder 4 Misfire Detected P0305Cylinder 5 Misfire Detected P0306Cylinder 6 Misfire Detected P0307Cylinder 7 Misfire Detected

P0318 — quick answers

Is it safe to drive with P0318?

Do not drive. Driveability guidance is not available for this code — treat as do not drive until checked.

Will P0318 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.