P0305 — Cylinder 4 Misfire Detected
Drivable short-term, but fix now to avoid damage.
What P0305 means
This code means the engine computer detected that cylinder 4 is misfiring, meaning the air-fuel mixture isn't igniting properly on that cylinder. It's commonly caused by a worn spark plug, a failing ignition coil, or a fuel injector problem, though vacuum leaks and low compression can also be to blame. Typical fixes include replacing the spark plug or coil for that cylinder, and it's usually repairable without major engine work.
Common symptoms
- Check engine light is on or flashing
- Rough idle or engine shaking
- Noticeable loss of power
- Engine hesitation or stumbling on acceleration
- Poor fuel economy and possible exhaust smell
Common causes
- Worn or fouled spark plug on cylinder 4
- Failing ignition coil for cylinder 4
- Clogged or faulty fuel injector
- Vacuum leak near cylinder 4
- Low compression from worn valves or rings
Typical repair cost
$100 – $500
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0305 code?
Only if you must, and not far. A misfire dumps unburned fuel into the exhaust and can ruin your catalytic converter. If the light is flashing, stop and tow the car; if it's steady, drive gently straight to a shop.
How much does it cost to fix a P0305 code?
Often $100 to $500. A spark plug or single ignition coil is on the low end, while injector replacement or compression-related repairs cost more. Diagnosing the exact cause first keeps you from replacing parts you don't need.
Is a P0305 code serious?
Yes, misfires are considered serious because they can quickly damage the catalytic converter, an expensive part. The good news is the underlying cause is usually a simple, affordable fix like a plug or coil.
Why is only cylinder 4 misfiring?
P0305 pinpoints cylinder 4 specifically, which usually means a component unique to that cylinder, like its spark plug, coil, or injector, is failing rather than an engine-wide problem. That makes it easier to track down.