P0305: Cylinder 5 Misfire Detected

What it means

Misfires concentrated on cylinder 5 (only present on engines with 5+ cylinders). Same diagnostic approach as P0301 — swap the suspect coil/plug with another cylinder.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control module detects misfires by monitoring changes in crankshaft speed as each cylinder contributes power. This code identifies repeated misfire activity associated with cylinder 5, which is present only on engines with at least five cylinders, so diagnosis should focus on that cylinder's ignition and mechanical condition.

Common causes

Most likely first.

1. Ignition coil for cylinder 5 failed
2. Spark plug worn or fouled

Symptoms

• Check engine light on or flashing
• Rough idle and uneven running
• Power loss, hesitation under acceleration
• Increased fuel consumption
• Possible smell of unburned fuel from exhaust

How to diagnose it

1. Read freeze-frame data and cylinder misfire counts to confirm cylinder 5 is the main source and note when the misfire occurs.
2. Inspect cylinder 5's spark plug, coil, connector, and wiring for wear, fouling, cracks, oil, or a poor electrical connection.
3. If the engine uses interchangeable coils, swap the cylinder 5 coil with another cylinder and check whether the misfire follows the coil.
4. If the misfire remains on cylinder 5, inspect its spark plug and verify ignition operation before investigating less common causes.
5. If ignition checks are sound, perform a compression or leak-down test on cylinder 5 and compare it with the manufacturer's specification.

Common fixes

• Repair a loose or damaged connection at cylinder 5's coil.
• Replace a worn or fouled cylinder 5 spark plug.
• Replace the cylinder 5 ignition coil if the misfire follows it during a swap test.
• Repair an engine mechanical problem identified by compression or leak-down testing.

Can I keep driving?

If the check-engine light is flashing, stop driving as soon as it is safe; an active cylinder 5 misfire can overheat and damage the catalytic converter. With a steady light and mild symptoms, drive only gently for a short distance and avoid acceleration under load.