The P0304 code in your 2018 BMW 3 Series indicates the engine management system has detected persistent misfires in cylinder 4. As a vehicle potentially carrying significant accumulated mileage, understanding both standard causes and age-related factors helps target diagnosis effectively for this F30 generation model.
Understanding P0304 in the 2018 3 Series (F30)
The 2018 3 Series F30 generation offers the B48 2.0L turbocharged four-cylinder (330i) or B46 in base models, with the B58 inline-six in M variants. For four-cylinder engines, cylinder 4 is at the rear. The F30 platform is well-understood with established service procedures and known characteristics.
Age-Related Considerations
Vehicles from 2018 may approach or exceed maintenance intervals. Spark plug replacement may be due regardless of visual appearance. Ignition coils degrade from years of heat cycling. Carbon buildup on intake valves accumulates progressively with direct injection engines—F30 models with significant mileage commonly show this condition.
Diagnostic Process
Identify your engine type. Review maintenance history noting mileage context. Use BMW-compatible diagnostics for comprehensive data. If spark plugs are original, replacement is advisable. Test ignition coil output. Consider carbon buildup inspection for higher-mileage F30 models.
Repair Solutions
Replace spark plugs with BMW-specified components—if original on higher-mileage vehicle, due regardless of appearance. Address carbon accumulation through walnut blasting if symptoms indicate. Replace degraded ignition coils. Consider comprehensive service if maintenance history is incomplete.