P0309 fault code: Cylinder 9 Misfire Detected
Driveability guidance is not available for this code — treat as do not drive until checked.
Can I DIY?
Professional-only boundary. We do not publish a diagnosis unique to P0309 yet. Confirm the code and book a garage.
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 P0309
Do not drive. Cylinder 9 is not firing correctly. This page has no unique diagnosis yet. If the engine management light flashes or the engine judders, stop.
Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.
- Cylinder 9 Misfire Detected: Registration number
- Cylinder 9 Misfire Detected: Exact code P0309 and any other misfire or coil codes
- Cylinder 9 Misfire Detected: Whether the engine management light is steady or flashing
- Cylinder 9 Misfire Detected: Whether the engine judders or loses power
What does P0309 mean?
P0309 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 “Cylinder 9 Misfire Detected”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.
Will P0309 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
Related fault codes
P0309 — quick answers
Is it safe to drive with P0309?
Do not drive. Driveability guidance is not available for this code — treat as do not drive until checked.
Will P0309 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.