P0304
P0304 Cylinder 4 Misfire
P0304 means the powertrain computer detected a misfire on cylinder 4. It is a symptom code, not proof that one specific part failed.
How urgent is P0304?
A flashing check engine light with P0304 should be treated as urgent.
Common symptoms
- Check engine light
- Rough idle
- Shudder on acceleration
- Loss of power
- Fuel smell
Likely causes
- Ignition coil failure
- Worn spark plug
- Faulty injector
- Vacuum leak
- Low compression
What to check before replacing parts
1
Swap coil and plug positions
2
Inspect wiring and connector
3
Check injector balance
4
Look for intake leaks
5
Run compression/leak-down test
Use the code with symptoms
A code points at the system, not always the failed part. Add your vehicle, mileage, symptoms, and whether the check engine light is steady or flashing so the AI diagnostic can narrow the next step.