Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.

P0305: Cylinder 5 misfire detected

The engine computer has detected that cylinder 5 is not contributing evenly.

What P0305 means

The engine computer has detected that cylinder 5 is not contributing evenly. The code identifies the affected cylinder, but not the failed part. Confirm the manufacturer’s cylinder-numbering layout before inspecting anything.

Can I still drive?

Treat this as urgent. A flashing engine-management light, violent shaking, stalling, obvious fuel smell or major power loss means stop and recover the vehicle: unburnt fuel can overheat the catalytic converter. If the light is steady, the engine remains smooth and no other warning is present, limit driving to a short, gentle journey for diagnosis; avoid high revs and heavy load.

Symptoms

  • Rough idle, vibration or an uneven exhaust note.
  • Hesitation, weak acceleration or increased fuel use.
  • Difficult starting or occasional stalling.
  • A steady or flashing engine-management light.
  • Fuel-like exhaust smell in a severe misfire.

Common causes

  • Worn, fouled, incorrectly gapped or damaged spark plug.
  • Failed ignition coil, plug lead or coil boot.
  • Injector fault, poor injector connection or restricted fuel delivery.
  • Air leak close to the affected intake runner.
  • Low compression from a valve, piston, head-gasket or valvetrain problem.
  • Less commonly, damaged wiring or a control-module fault.

Safe first checks

  • Save all codes and freeze-frame data before clearing them. Confirm which physical cylinder is number
  • With the ignition off and engine cold, look for a loose coil or injector connector, damaged insulation, corrosion, and oil or coolant in the plug well. Check accessible intake and vacuum hoses. Coil or plug swap-testing should be done only by someone competent and only with the ignition off; never handle live ignition parts.

Typical UK fix cost

Allow roughly £90–£180 for diagnosis. A plug or straightforward coil repair may bring the total to £130–£350; an injector or wiring repair is often £250–£700. Compression, cylinder-head or internal-engine work can exceed £1,000–£3,000+ and must be quoted after testing.

Related models

This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.

Related fault codes

Sources

A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.