P0304 — Cylinder 4 Misfire Detected
High severityWhat it means
P0304 means the engine control unit counted repeated misfires in cylinder 4 specifically. Because it is isolated to one cylinder, the cause is usually a part that serves only cylinder 4 — its spark plug, ignition coil or injector.
Common symptoms
- Rough idle and engine shake
- Hesitation or power loss under load
- Flashing or steady check engine light
- Fuel smell from the exhaust in severe cases
Likely causes
- Worn or fouled spark plug in cylinder 4
- Failing ignition coil on cylinder 4
- Clogged or leaking injector on cylinder 4
- Low compression in cylinder 4
What to check first
- Swap the cylinder 4 coil with a neighbouring cylinder and see if the misfire follows
- Inspect and replace the cylinder 4 spark plug if worn
- Run a compression test on cylinder 4 if ignition and fuel check out
Can you keep driving?
Misfires can quickly overheat the catalytic converter. Keep driving to a minimum and stop if the check engine light flashes.
Frequently asked questions
What is the most common cause of P0304?
The most likely cause is: Worn or fouled spark plug in cylinder 4. Several other faults can set P0304 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P0304 and keep driving?
Clearing P0304 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P0304?
P0304 is a high-severity code. Diagnose and repair it as soon as possible, because continuing to drive can cause further damage or leave you stranded.
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