P0304 Hyundai Sonata
Cylinder 4 Misfire Detected · Powertrain Code · High · Repair: Easy
What is P0304?
Misfire detected in cylinder 4. Typically caused by a worn spark plug, bad ignition coil, faulty fuel injector, or low compression in that cylinder.
When the Hyundai Sonata triggers code P0304 (cylinder 4 misfire detected), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the Hyundai Sonata.
This repair is rated easy, meaning basic tools, no lift needed.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Hyundai Sonata.
Common Causes on Hyundai Sonata
- Failed ignition coil on cylinder 4
- Worn iridium spark plug on cylinder 4
- Fuel injector failure on cylinder 4
- Vacuum leak near cylinder 4 intake runner
- Low compression due to valve seat recession
Symptoms
- Check Engine Light on or flashing
- Rough idle
- Engine vibration
- Reduced power
- Possible catalytic converter damage if ignored
Notes for Hyundai Sonata
Replace all spark plugs at once if they are past the recommended 30k-mile interval for iridium plugs.