What does OBD code P0301 mean?
P0301 is a misfire detection code for Cylinder 1 specifically (P0300 is a random/multiple cylinder misfire). The ECU detects that Cylinder 1 is not firing correctly by monitoring crankshaft speed variations. A misfire causes rough idle, loss of power, hesitation, increased fuel consumption, and the engine management light. A flashing EML with P0301 means an active misfire that can damage the catalytic converter — do not ignore it.
Likely causes
Faulty spark plug in cylinder 1
Fouled, worn, or incorrectly gapped spark plug is the most common cause of a single-cylinder misfire
Faulty ignition coil on cylinder 1
On coil-on-plug systems, each cylinder has its own coil — failing coil stops firing that cylinder
Fuel injector fault on cylinder 1
Blocked or leaking injector prevents correct fuel delivery to the cylinder
Low compression in cylinder 1
Worn piston rings, valves, or head gasket leak — confirmed by compression test
Wiring or connector fault
Corroded or broken connector to coil or injector on cylinder 1
Repairs you may need
Typical cost range: £60–£400 — Spark plugs (full set): £60–200. Single coil: £80–200. Injector clean/replace: £100–250.
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