P0305: Cylinder 5 Misfire Detected

Common causes

• A worn spark plug in cylinder 5
• A failing ignition coil or plug wire for that cylinder
• A clogged or failing fuel injector
• A vacuum leak near that cylinder's intake port
• Low compression from a valve or head gasket problem (less common)

Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.

Symptoms

• Rough idle or shaking
• Loss of power or hesitation
• A flashing check engine light during heavy misfiring
• Worse fuel economy

Is it safe to drive?

If the check engine light is flashing, ease off and avoid hard driving: a heavy misfire can overheat and ruin the catalytic converter. A steady light with a mild misfire should still be checked soon.

How to check it with a scanner

1. Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
2. Find which cylinder is number 5 for your engine (it varies by maker); a repair manual or service site shows the firing order layout.
3. With the engine off, swap the cylinder 5 coil with a neighbouring cylinder, clear the code and drive. If the misfire moves to the other cylinder, the coil is the problem.
4. Pull and inspect the spark plug for wear, oil or carbon. If the plug and coil are fine, check the injector and do a compression test.
5. After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.

A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.

Questions

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