OBD-II code guide
P0304 Cylinder 4 Misfire Detected
P0304 means the engine computer has detected misfire activity on cylinder 4.
What it means
Cylinder 4 is losing combustion events and may send unburned fuel into the exhaust.
Common symptoms
- Flashing check engine light
- Rough idle
- Engine vibration
- Poor acceleration
- Catalyst damage risk
Likely causes
- Failed coil
- Worn spark plug
- Injector problem
- Vacuum leak
- Compression loss
First checks
- Identify the correct cylinder location.
- Inspect ignition parts before replacing expensive components.
- Check for P0420 if the misfire was driven for a while.
- Arrange towing if the engine runs very rough.