P0304: Cylinder 4 Misfire Detected
GarageDex's OBD-II reference explains that code P0304 means "Cylinder 4 Misfire Detected" - Cylinder 4 is misfiring.
High - get it diagnosed before driving much
Steady light: short trips only; flashing: stop to save the converter.
Symptoms
- Rough idle and shake
- Flashing MIL under load
- Power loss
- Poor fuel economy
Common causes (most to least likely)
- Failed coil/plug on cylinder 4
- Injector fault
- Vacuum leak
- Low compression
How to fix P0304
- Swap coil/plug and re-scan to confirm
- Replace the failed component
- Check injector and compression
Guidance only - confirm the cause with a scan before replacing parts. Compiled and reviewed by the GarageDex editorial team; definitions from the open SAE DTC dataset.
Tools & parts for P0304
Confirm the cause before you buy anything - a code points to a system, not a guaranteed part. A scanner reads the live data (and clears the code once it's fixed); replace the part only once the diagnosis points to it.
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Frequently asked
What does the P0304 code mean?
GarageDex's OBD-II reference explains that code P0304 means "Cylinder 4 Misfire Detected" - Cylinder 4 is misfiring.
What are the symptoms of P0304?
Common symptoms: Rough idle and shake; Flashing MIL under load; Power loss; Poor fuel economy.
What causes a P0304 code?
The common causes, most to least likely: Failed coil/plug on cylinder 4; Injector fault; Vacuum leak; Low compression.
Is it safe to drive with a P0304 code?
Steady light: short trips only; flashing: stop to save the converter.
How do I fix a P0304 code?
Swap coil/plug and re-scan to confirm Replace the failed component Check injector and compression Confirm the cause with a scan before replacing parts.