P0305 — Cylinder 5 Misfire Detected

P0305 means cylinder 5 is misfiring. Start with the cheapest possibilities in order: spark plug, ignition coil, then injector, then compression.

Cost range: $50–$1,200. Severity: high. Safe to drive? No if the light is flashing — raw fuel destroys the catalytic converter within minutes.

Most common causes of P0305

1. Worn spark plug — Swap plugs between cylinders — if the misfire follows, you found it. ($20–$120)
2. Failed ignition coil — Same swap test works for coil-on-plug setups. ($80–$350)
3. Clogged or dead fuel injector — Confirm with an injector balance test. ($200–$700)
4. Vacuum leak at the intake runner — Leans out one cylinder specifically. ($100–$400)
5. Low compression — Burnt valve or ring wear — the expensive outcome. ($800–$3,000)

Symptoms drivers report with P0305

• Shaking at idle
• Flashing check engine light
• Power loss
• Fuel smell