Code P0303 indicates that the engine control module has detected a misfire occurring specifically in cylinder number 3. This means the combustion process in that cylinder is not occurring completely or consistently.
A worn spark plug, failed ignition coil, or damaged spark plug wire preventing a strong spark in cylinder 3.
A clogged, leaking, or electrically failed fuel injector preventing proper fuel delivery to the cylinder.
Worn piston rings, a burnt or leaking valve, or a blown head gasket resulting in low cylinder compression.
Air leaking into the intake manifold specifically near the cylinder 3 intake port, causing a lean misfire.
A failure in the engine computer's driver circuit for the cylinder 3 injector or coil; this is very rare.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
It is not recommended, as unburnt fuel from the misfiring cylinder can enter the exhaust and overheat or destroy the catalytic converter.
While spark plugs are the most common cause, the misfire could also be caused by a failed coil, injector, or internal engine wear.
No. PCM failure is extremely unlikely for a single-cylinder misfire. Exhaust all ignition, fuel, and mechanical possibilities before considering the computer.