Parts
$15–150
P0303 — Cylinder 3 Misfire Detected
STOPIs it safe to drive? Cylinder 3 is misfiring. Don't drive hard on a flashing light — the cat pays for it.
What P0303 means
Cylinder 3 failing to fire cleanly; isolated, so it's that cylinder's ignition, fuel, or mechanical health.
Most likely causes (in order)
- Plug or coil on cylinder 3
- Injector for cylinder 3
- Low compression on cylinder 3
- Local vacuum leak
Symptoms you might notice
- Rough idle
- Hesitation
- Fuel smell
What to check first
Swap parts with an adjacent cylinder to isolate; compression-test if spark+fuel check out.
Repair cost & difficulty
Labor
0.5–2 hr
Difficulty
DIY-friendly