P0304 — Cylinder 4 Misfire Detected
Drivable short-term, but fix now to avoid damage.
What P0304 means
P0304 means the engine computer detected a misfire in cylinder number 4. That cylinder isn't igniting its air-fuel mixture properly, so the engine runs rough and loses power. Being cylinder-specific, the cause is usually a worn ignition or fuel component on cylinder 4.
Common symptoms
- Check engine light on or flashing
- Rough idle and vibration
- Loss of power and hesitation
- Engine stumbles or jerks
- Higher fuel consumption
Common causes
- Worn or fouled spark plug on cylinder 4
- Failing ignition coil on cylinder 4
- Clogged or faulty fuel injector
- Damaged spark plug wire or boot
- Vacuum leak near cylinder 4
- Low compression in cylinder 4
Typical repair cost
$80 – $450
Varies by vehicle and root cause.
Frequently asked questions
Can I drive with P0304?
Only briefly and gently. If the engine light is flashing, stop and have the car towed to avoid expensive catalytic converter damage.
How much does it cost to fix a P0304?
Usually $80-$300 for a spark plug or coil on cylinder 4 with labor. Injector or compression repairs can push it toward $450 or more.
Is a P0304 serious?
It can be. A continuing misfire risks overheating and ruining the catalytic converter, so it's wise to fix it without much delay.
Why did only cylinder 4 misfire?
A single-cylinder code usually means a part dedicated to that cylinder, like its coil, plug, or injector, has worn out or failed, rather than an engine-wide problem.