Drivable short-term, but fix now to avoid damage.
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.
$100 – $500
Varies by vehicle and root cause.
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.
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.
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.
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.