What P0304 means
Cylinder 4 specifically is misfiring. Because it is a single cylinder, the cause is usually a component on that cylinder.
Common causes
- Failed coil or plug on cylinder 4
- Leaking or clogged injector
- Low compression on that cylinder
How it is usually fixed
- 1Swap the coil and plug with a neighbouring cylinder and clear the code — if the misfire follows, you found the part
- 2Test injector operation
- 3Compression and leak-down test if the misfire stays
Other common codes
- P0011 — Camshaft Position A – Timing Over-Advanced (Bank 1)
- P0030 — HO2S Heater Control Circuit (Bank 1, Sensor 1)
- P0101 — Mass Air Flow Circuit Range/Performance
- P0113 — Intake Air Temperature Sensor Circuit High
- P0118 — Engine Coolant Temperature Sensor Circuit High
- P0131 — O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
Code information is general guidance, not a diagnosis for a specific vehicle. Confirm with live data and manufacturer test procedures before replacing parts.