P0304: Cylinder 4 Misfire Detected

What does P0304 mean?

The engine computer has detected misfires only on cylinder 4. On an inline-four this is usually the cylinder at the transmission end, which can be harder to reach and is easily overlooked during plug changes. On a V engine, check the service manual for its location.

Generic OBD-II definition: Cylinder 4 Misfire Detected. Confirm applicability in your vehicle service information.

Common causes

• Spark plug for cylinder 4 not replaced or not torqued correctly during the last tune-up
• Ignition coil for cylinder 4 failing
• Injector for cylinder 4 dirty or not opening
• Harness damage near the back of the engine from heat
• Low compression or a leaking head gasket near cylinder 4

Symptoms

• Rough idle and stumbling at low speed
• Hesitation when pulling away
• Possible coolant loss if a head gasket is involved

Can I keep driving with P0304?

Severity: High Stop or minimize driving and get it looked at right away.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Verify the cylinder 4 plug is the correct type, gapped and tightened properly
• Swap cylinder 4's ignition coil with a neighboring cylinder's coil, clear codes, and drive: if the code moves to that cylinder, the coil is bad
• Check the harness near the firewall end for melted or rubbed-through insulation
• If you're also losing coolant, test for a head gasket leak before replacing ignition parts