P0303
Cylinder 3 Misfire Detected
Ignition / misfire
Generic OBD-II
High
What it means
P0303 means the engine control module detected a misfire specifically in cylinder 3 — the fuel isn't burning properly in that cylinder, so the engine runs rough and loses power. The usual culprit is a worn spark plug or failing ignition coil on that cylinder. A sustained misfire can overheat and damage the catalytic converter, so address it promptly.
High
Can I keep driving? Not for long — a flashing check-engine light means cylinder 3 is actively misfiring; drive as little as possible to avoid catalytic converter damage.
Common symptoms
What you'll notice
- Check-engine light on (often flashing during an active misfire)
- Rough idle, shaking, or stumbling
- Reduced power and hesitation on acceleration
- Occasional stalling at idle
Common causes
Most likely first
- Worn spark plug in cylinder 3Likely
- Failing ignition coil on cylinder 3Common
- Clogged or leaking fuel injector on cylinder 3Common
- Vacuum leak affecting that cylinderLess often
- Low compression in cylinder 3 (valve or ring wear)Less often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data to confirm the miss is on cylinder 3.
- Swap the coil and plug with an adjacent cylinder — if the misfire follows, you've found it.
- Replace the worn spark plug and/or ignition coil for that cylinder.
- Test the injector for that cylinder (resistance and spray).
- If it persists, run a compression test to check for mechanical wear. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0303?+
No — especially with a flashing light. An active misfire dumps raw fuel into the exhaust and can quickly overheat the catalytic converter.
Can I just clear P0303?+
It returns within a few drive cycles until the plug, coil, injector, or compression issue on cylinder 3 is fixed.
Related codes
Often seen with P0303
Read & clear P0303 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX