What P0304 Means
The engine control module has detected a misfire specifically in cylinder 4.
Common Causes
- Worn or fouled spark plug in that cylinder
- Failing ignition coil for that cylinder
- Faulty or clogged fuel injector for that cylinder
- Low compression in that cylinder
Symptoms You Might Notice
- Rough idle
- Engine hesitation under load
- Check engine light, flashing if severe
- Reduced power
What to Check First
- 1
Swap the spark plug and coil from cylinder 4 with a known-good cylinder to isolate the fault
- 2
Check the fuel injector for that cylinder
- 3
Run a cylinder-specific compression test if electrical parts test fine