The P0304 code indicates that the engine control module has detected a misfire occurring specifically in cylinder 4. This means the cylinder is not completing its combustion cycle effectively, often detected by an irregular crankshaft rotation speed.
A worn-out spark plug or a failed ignition coil/spark plug wire prevents the spark required for combustion in cylinder 4.
A clogged or electronically failed fuel injector prevents the correct amount of fuel from entering the cylinder.
Low compression caused by worn piston rings, a leaking valve, or a blown head gasket prevents effective combustion.
An intake manifold leak specifically near cylinder 4 allows unmetered air to enter, leaning out the mixture.
A rare failure in the engine computer's driver circuit may result in an incorrect signal to the injector or coil.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
While a spark plug is a common cause, it is recommended to swap the coil or plug to another cylinder first to confirm the fault follows the part.
No. It is extremely rare for a PCM to fail in a way that affects only one cylinder; the issue is almost always a failed plug, coil, injector, or mechanical compression loss.
Yes. Unburned fuel from a misfiring cylinder can enter the exhaust system and cause permanent damage to the catalytic converter.