What does P0304 mean?
The control module detected a condition described as “Cylinder 4 misfire detected”. The code identifies the affected area, but it does not by itself prove which component has failed. The code describes the detected condition, not a guaranteed failed part. A reliable diagnosis also considers related codes, freeze-frame data, live values and the actual symptoms.
Possible causes
- Faulty spark plug, ignition coil or lead
- Injector or fuel-supply problem
- Unmetered air or incorrect mixture formation
- Compression loss or mechanical engine damage
Common symptoms
- Flashing or steady check-engine light
- Severe hesitation and power loss
- Rough idle
- Fuel smell and possible catalyst damage
Sensible next checks
- Avoid high load and stop safely if the check-engine light flashes
- Read misfire counters and freeze-frame data
- Compare ignition components cylinder by cylinder instead of replacing blindly
- Check compression and injection if the fault returns
Why does it return after clearing?
Clearing the code only removes the stored entry. If the underlying condition remains, the control module will set the code again after the next relevant monitor cycle. Save the data first, diagnose the cause, repair it and only then clear the code.