P0304 — Cylinder 4 Misfire Detected
Misfires concentrated on cylinder 4. A cylinder-specific code points away from shared causes (fuel pressure, MAF) toward components dedicated to that cylinder — coil, spark plug, injector, compression. Verify by swapping the suspected coil/plug to a different cylinder; if the code follows, the part is bad.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Ignition coil
- Spark plug
- Fuel injector
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Ignition coil for cylinder 4 failed
- Spark plug for cylinder 4 worn or fouled
- Cylinder 4 injector clogged
Possible symptoms
- Check engine light on or flashing
- Rough idle and uneven running
- Power loss, hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from exhaust
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Related codes
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.