P0301 Fault Code: What It Means and What To Do
Cylinder 1 misfire detected
What does P0301 mean?
P0301 means the engine control unit has detected a misfire specifically in cylinder 1 — the first cylinder in the engine's firing order. A misfire is when the air/fuel mixture in that cylinder fails to ignite correctly, or ignites unevenly. The result is a power stroke that produces less energy than it should, which you typically feel as a shake or judder, especially at idle or under load.
Unlike P0300 (random multiple misfires), P0301 is specific — it points directly at cylinder 1, which usually makes the diagnosis much more straightforward. You might feel a rhythmic roughness at idle, and the car may feel notably down on power when accelerating.
Common causes
- Worn or fouled spark plug (cylinder 1) — by far the most common cause. A plug that's past its service life or contaminated with oil can no longer generate a reliable spark.
- Faulty ignition coil (cylinder 1) — the coil amplifies the electrical signal to fire the plug. A weak coil causes the plug to misfire intermittently or constantly.
- Bad fuel injector (cylinder 1) — a clogged or leaking injector delivers the wrong amount of fuel, upsetting the mixture in that cylinder.
- Low compression in cylinder 1 — worn piston rings, a burnt valve, or a blown head gasket can all cause low compression, making the mixture too weak to ignite properly.
- Wiring fault — damaged or corroded wiring to the coil or injector on cylinder 1 can interrupt the signal.
Typical UK repair costs
UK labour rates are typically £80–£120 per hour. Costs vary by vehicle and region.
What to do next
If the warning light is flashing, stop driving as soon as it is safe — prolonged misfiring can destroy the catalytic converter. If it's steady, book it in soon.
The cheapest first step is to check when the spark plugs were last replaced. If they're overdue, replacing the plug on cylinder 1 (or the full set) is quick and affordable. A mechanic can do the coil-swap test to distinguish between a plug and coil fault in minutes before ordering parts.
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