Parts
$15–150
P0304 — Cylinder 4 Misfire Detected
STOPIs it safe to drive? Cylinder 4 is misfiring. Flashing light = active damage, take it easy.
What P0304 means
Cylinder 4 isn't firing cleanly. Chase the plug, coil, injector, or compression on cylinder 4.
Most likely causes (in order)
- Plug or coil on cylinder 4
- Injector for cylinder 4
- Low compression
- Local vacuum leak
Symptoms you might notice
- Rough idle
- Power loss
- Fuel smell
What to check first
Swap-and-test with a neighbor cylinder; compression last.
Repair cost & difficulty
Labor
0.5–2 hr
Difficulty
DIY-friendly