P0303 Cylinder 3 Misfire Detected — Diesel Causes & Fix

What Does P0303 Mean?

P0303 is the cylinder-specific version of the P0300 random-misfire code: the crankshaft sensor shows cylinder 3 repeatedly failing to contribute torque. Diesels do not have ignition coils, so the usual petrol causes do not apply — the injector is the first suspect, followed by compression and, on cold starts, the glow plug.

P0303 at a Glance

• What it means: The ECU has detected repeated combustion failures in cylinder 3.
• Most common cause: On diesels: a worn or electrically failed injector; also compression loss or glow plug faults when cold.
• Severity: Serious if persistent — raw fuel can damage the DPF and catalyst.
• Can you drive?: Only short distances. A hard misfire should be diagnosed promptly.
• Typical repair cost: £100-£350 for injector replacement; less for wiring or glow plug fixes.