When your 2020 Subaru Ascent displays the P0304 code, the engine control module has detected recurring misfires in cylinder 4. The three-row SUV's turbocharged boxer engine requires understanding of both forced induction and Subaru's horizontally-opposed design for effective diagnosis.
Understanding P0304 in the 2020 Ascent
The 2020 Ascent features the 2.4L FA24 turbocharged boxer four-cylinder producing 260 horsepower. This is the only engine option for the Ascent. Subaru's horizontally-opposed configuration positions cylinder 4 at the rear of the left (driver's) bank. The turbocharged operation adds specific diagnostic considerations.
Turbocharged Boxer Misfire Causes
The boosted 2.4L faces elevated ignition demands from higher cylinder pressures. Spark plugs must reliably ignite compressed air-fuel charges. Ignition coils require sufficient output for turbocharged conditions. Direct injection contributes to carbon accumulation on intake valves. The three-row SUV's family duty may include varied driving conditions.
Diagnostic Approach
Retrieve all codes including boost-related faults. Analyze freeze frame data noting engine load conditions. Locate cylinder 4 on the left bank rear position. Test ignition coil output ensuring capability for turbocharged demands. Inspect spark plug condition. Verify fuel injector operation.
Repair Solutions
Install Subaru-specified spark plugs rated for turbocharged applications. Clean spark plug wells before removal. Replace degraded ignition coils. Address fuel system concerns. Turbocharged engines benefit from quality components.