The 2020 Subaru Outback triggering P0304 indicates a cylinder 4 misfire in the horizontally-opposed boxer engine. This unique engine layout requires understanding of cylinder positioning and access for proper diagnosis.
Boxer Engine Cylinder Layout
The Outback's boxer engine positions cylinders horizontally—two on each side. Cylinder 4 is at the rear of the passenger-side bank (right side). This position can affect access for spark plug service and may experience different oil drainage patterns than vertical engines.
Outback Engine Options
The 2020 Outback offers 2.5-liter and 2.4-liter turbocharged boxer engines. Both use direct injection. Cylinder numbering follows standard Subaru convention with 1-3 on one bank and 2-4 on the opposite bank.
Ignition System Testing
Subaru's coil-on-plug ignition places coils above the horizontal cylinders. Swap the cylinder 4 coil with cylinder 2—if the misfire moves, replace the coil. Access may require removing engine covers or the intake plenum.
Spark Plug Service Considerations
The horizontal cylinder orientation means spark plugs face outward rather than up. Oil can potentially drain toward plug wells over time. Inspect plug wells for oil contamination that could cause misfires.
Fuel Injector Testing
Direct injection operates at high pressure for precise fuel delivery. Use Subaru diagnostic equipment to test injector operation. Compare cylinder 4's response to other cylinders.
Repair Costs
Ignition coil replacement costs $100-180 at Subaru dealers. Complete spark plug service runs $200-350 due to boxer engine access. Fuel injector replacement ranges $250-500 per injector.