P0305 — Cylinder 5 misfire detected

P0305 identifies uneven combustion contribution from cylinder 5, without identifying the failed part. Investigate ignition on spark-ignition engines; on diesel engines focus on injection and mechanical condition, without assuming an ignition coil.

Affected system: Powertrain

Symptoms

• Rough running, hesitation or reduced power.
• Steady/flashing engine lamp; possible hard starting and increased consumption.

Possible causes

• On gasoline engines: spark plug, coil or high-voltage insulation fault, subject to testing.
• Injector, fuel supply or unmetered air; low compression or poor cylinder sealing.

What to check

• Locate cylinder 5 using OEM numbering; record freeze-frame and all cylinder misfire counters.
• Establish cold/hot/load conditions and address related fuel/synchronisation codes first.
• On gasoline engines inspect the plug/connections; if allowed, swap a compatible coil and check whether the misfire follows.
• Use the approved injector/contribution test; on diesel use specified correction/leak-off tests without opening pressurised lines.
• If the fault remains on cylinder 5, test intake sealing, compression and cylinder leakage; avoid loading an engine with a flashing lamp.

Also written as: P0305-00, P030500, PO305 (some scan tools add the fault-type byte, e.g. -00).