P0303 on a Hyundai: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

You can usually drive short distances with a steady light, but stop right away if the light flashes — a severe misfire can damage the catalytic converter.

What P0303 means on a Hyundai

On a Hyundai, P0303 means the computer has flagged cylinder 3 for misfiring. The problem is local to cylinder 3 — its spark plug, ignition coil, or fuel injector — rather than a system-wide issue.

Is P0303 common on Hyundais?

P0303 shows up on Hyundais with higher mileage, often on the Elantra, Sonata, and Tucson. Worn spark plugs and failing coil-on-plug ignition coils are the usual causes. Clogged or leaking fuel injectors are less common but possible.

Commonly reported on: Elantra, Sonata, Tucson, Santa Fe.

Symptoms

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

Common causes

most common: Worn or fouled spark plug on cylinder 3
common: Failing ignition coil on cylinder 3
common: Clogged or leaking fuel injector on cylinder 3
less common: Low compression in cylinder 3

How to fix it

Fix	DIY?	Typical cost
Swap the cylinder 3 coil and plug with another cylinder to confirm which part is bad	Yes	$0–20
Replace the cylinder 3 spark plug	Yes	$10–50
Replace the cylinder 3 ignition coil	Yes	$50–200
Have cylinder 3 compression-tested	Mechanic	$100–200