When your 2020 Subaru Legacy displays the P0304 code, the engine control module has detected recurring misfires in cylinder 4. The first year of the seventh-generation Legacy offers multiple boxer engine options, and understanding your specific configuration enables targeted diagnosis.
Understanding P0304 in the 2020 Legacy
The 2020 Legacy marks the first year of a complete redesign featuring the 2.5L FA25 boxer four-cylinder as standard or the 2.4L FA24 turbocharged boxer in XT trims. Both horizontally-opposed configurations position cylinder 4 at the rear of the left (driver's) bank. This unique architecture affects service approach.
Redesigned Platform Considerations
First-year redesigned vehicles may reveal unexpected issues as miles accumulate. The new FA-series engines replaced the FB-series from previous generations. Monitor for technical service bulletins addressing widespread concerns. Standard ignition and fuel causes remain the most common P0304 sources.
Diagnostic Approach
Identify your engine—2.5L or 2.4L turbo. Retrieve all codes and freeze frame data. Locate cylinder 4 on the left bank rear position. Test ignition coil output and spark plug condition. Verify fuel injector operation. Consider mileage accumulation since the 2020 launch.
Repair Solutions
Install Subaru-specified spark plugs for your engine type. Clean spark plug wells before removal. Replace degraded ignition coils. Address fuel system concerns. New FA-series engines may have different specifications than previous FB-series.