P0303 Code: Cylinder 3 Misfire Detected

🟠 Moderate severity · drivable

If the light is flashing, stop immediately. Otherwise a short drive to a shop is usually fine.

What P0303 means

Cylinder 3 is misfiring — it isn't firing properly. A specific-cylinder misfire usually points to a part on that cylinder, most often the spark plug or ignition coil.

Symptoms

Check engine light on (flashing if severe)
Rough idle or shaking
Loss of power
Poor fuel economy

Common causes

most common: Bad spark plug on cylinder 3
most common: Failing ignition coil or plug wire for cylinder 3
common: Clogged or leaking fuel injector on cylinder 3
less common: Vacuum leak affecting that cylinder
less common: Low compression in cylinder 3

How to fix it

Fix	DIY?	Typical cost
Replace the cylinder 3 spark plug	Yes	$10–50
Replace the cylinder 3 ignition coil (or swap it to confirm)	Yes	$50–200
Clean or replace the cylinder 3 fuel injector	Mechanic	$100–300
Run a compression test on cylinder 3	Mechanic	$100–200