P0303 on a Subaru: 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 Subaru
On a Subaru, P0303 means the computer has flagged cylinder 3 for misfiring. The fault is local to cylinder 3 — its spark plug, ignition coil, or fuel injector — rather than a system-wide problem.
Is P0303 common on Subarus?
P0303 appears on Subarus with higher mileage, often on the Outback, Forester, and Impreza. Worn spark plugs and failing coil-on-plug ignition coils are the usual causes of a single-cylinder misfire. On the boxer engine the plugs sit low on the sides of the engine, which makes them harder to reach than on most cars.
Commonly reported on: Outback, Forester, Impreza, Legacy.
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 |
|---|---|---|
| Replace the cylinder 3 spark plug | Yes | $20–60 |
| Replace the cylinder 3 ignition coil | Yes | $60–200 |
| Have cylinder 3 compression-tested | Mechanic | $100–200 |
Frequently asked questions
Other common Subaru codes
P0303 on other brands
Looking for the full (non-brand-specific) guide? See the P0303 code page →
Browse all Subaru codes: Subaru hub →
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.