P0301 fault code: Cylinder 1 Misfire Detected
Last updated · OBDCode UK editorial
Limit driving while P0301 is stored. If the engine management light flashes or the car judders, stop and arrange recovery — unburnt fuel can damage the catalytic converter.
Can I DIY?
Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage.
Some checks may be possible for a careful DIY driver with the right tools and a safe place to work. Stop if anything feels beyond your skill or kit.
On a 12V battery: disconnect negative first, reconnect negative last. Prevent sparks and short circuits. Stop if the battery is damaged or sits near orange high-voltage cables.
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.
Never idle in a closed garage to read codes — an open door is not enough. CO is odourless and can kill. Run diagnostics in open air. Headache or nausea with exhaust smell: get fresh air and stop.
What does P0301 mean?
P0301 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 1 Misfire Detected”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.
How to diagnose P0301 yourself
- Confirm P0301 and freeze-frame: Scan with an OBD-II reader in open air. Note whether P0301 is current, freeze-frame (rpm, load, coolant temperature), and any other cylinder misfire or coil codes. Stop if: The engine management light is flashing, the engine judders badly, or you cannot identify which cylinder is number 1.
Park safely and switch off before locating the socket. Its position varies, so use the vehicle handbook and never force or dismantle trim. - Check for a flashing engine management light: With the engine running outdoors, watch the engine management light. Note whether it flashes and whether the car judders or loses power. Do not idle in a closed garage. Stop if: The light flashes, the engine judders, or exhaust fumes are inside the cabin — stop and arrange recovery.
A flashing engine management light means stop safely and arrange recovery, whether or not you feel judder. A steady light still needs prompt diagnosis, and becomes a stop if it starts to flash, judder or lose power.
Will P0301 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.
What the MOT data says
These figures are copied from the MOT fail cohort for the certificate wording below. They are not a diagnosis of this car.
Certificate wording: “Malfunction indicator lamp Engine MIL illuminated indicating a malfunction”.
Of 391,384 Class 4 vehicles that failed a 2024 MOT on that wording, 14.8% (95% CI 14.7–14.9) failed on the same wording again in 2025. The not-tested gap versus control was 11.5 points.
Certificate wording: “Catalyst emissions Lambda coefficient outside the default limits or the range specified by the manufacturer”.
Of 166,607 Class 4 vehicles that failed a 2024 MOT on that wording, 7.5% (95% CI 7.4–7.6) failed on the same wording again in 2025. The not-tested gap versus control was 13.4 points.
Engine management light MOT outcomes
Related guides
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P0301 — quick answers
Is it safe to drive with P0301?
Limit driving. Limit driving while P0301 is stored. If the engine management light flashes or the car judders, stop and arrange recovery — unburnt fuel can damage the catalytic converter.
Can I fix P0301 myself?
Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage. Basic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.
Will P0301 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.