The P0304 code in your 2023 Subaru Legacy indicates the powertrain control module has detected persistent misfires in cylinder 4. Understanding the midsize sedan's boxer engine options enables targeted diagnosis for effective repair of this combustion problem.
Understanding P0304 in the 2023 Legacy
The 2023 Legacy features 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. Subaru's engine management precisely identifies the misfiring cylinder through crankshaft velocity analysis.
FA-Series Engine Considerations
The FA-series engines offer improved performance and efficiency over previous FB-series. The turbocharged 2.4L faces higher ignition demands from boosted pressures. Both engines use direct injection with associated carbon accumulation potential. Quality ignition components ensure reliable operation.
Diagnostic Process
Identify your engine—2.5L or 2.4L turbo. Retrieve all codes and analyze freeze frame conditions. Locate cylinder 4 on the left bank rear position. For turbo models, check for boost-related codes. Test ignition coil output and spark plug condition. Verify fuel injector operation.
Repair Implementation
Install Subaru-approved spark plugs for your engine type. Clean spark plug wells before removal. Replace ignition coils testing outside specifications. Address fuel system concerns.