P0304 Subaru Forester
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 Subaru Forester 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 Subaru Forester.
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 Subaru Forester.
Common Causes on Subaru Forester
- Failed ignition coil on cylinder 4 (driver side rear on boxer)
- Worn spark plug on cylinder 4
- Fuel injector failure on cylinder 4
- Low compression from head gasket or valve issue on cylinder 4
Symptoms
- Check Engine Light on or flashing
- Rough idle
- Engine vibration
- Reduced power
- Potential catalytic converter damage if ignored
Notes for Subaru Forester
Replace all four spark plugs at once if past the 60k-mile service interval; Subaru boxer plugs are easy to access.