P0303 Subaru Forester
Cylinder 3 Misfire Detected · Powertrain Code · High · Repair: Easy
What is P0303?
Misfire detected in cylinder 3. 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 P0303 (cylinder 3 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
- Worn spark plug on cylinder 3 (driver side front on boxer)
- Failed ignition coil on cylinder 3
- Fuel injector clogging on cylinder 3
- Head gasket leak affecting cylinder 3 compression
Symptoms
- Check Engine Light flashing during misfire
- Rough idle
- Power loss
- Vibration increase beyond normal boxer character
Notes for Subaru Forester
Cylinder 3 on boxer engines is driver side front; swap the coil to cylinder 1 to verify if the misfire follows the coil.