P0303 — Cylinder 3 Misfire Detected
Drivable short-term, but fix now to avoid damage.
What P0303 means
P0303 means the engine computer detected a misfire in cylinder number 3. That cylinder isn't burning its fuel mixture correctly, so the engine loses smoothness and power. As a cylinder-specific code, it usually points to a worn spark plug, coil, or injector on cylinder 3.
Common symptoms
- Check engine light on or flashing
- Rough idle and shaking
- Hesitation and weak acceleration
- Engine jerks under load
- Increased fuel consumption
Common causes
- Worn or fouled spark plug on cylinder 3
- Failing ignition coil on cylinder 3
- Clogged or leaking fuel injector
- Bad spark plug wire or boot
- Vacuum leak near cylinder 3
- Low compression in cylinder 3
Typical repair cost
$80 – $450
Varies by vehicle and root cause.
Frequently asked questions
Can I drive with P0303?
Only short distances and carefully. A flashing engine light means stop driving and tow the car to prevent catalytic converter damage.
How much does it cost to fix a P0303?
Typically $80-$300 for a plug or coil on cylinder 3 with labor. Injector replacement or compression repairs can cost more, up to $450 or beyond.
Is a P0303 serious?
It can become serious. A lingering misfire can overheat and destroy the catalytic converter, so addressing it quickly is the smart move.
Will a P0303 cause my car to fail an emissions test?
Yes. An active misfire code and the resulting incomplete combustion will usually cause a failed emissions or smog test until it's repaired.