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.

Real-world scan data

Seen in

11,881

scans in the past year

Found in

1.9%

of scans

3.4%

of scans that found faults

Appears alongside · share of P0303 scans

P0300in 76.8% of scans

P0301in 52.7% of scans

P0302in 51.4% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.