The P0304 diagnostic trouble code on your 2018 Honda Civic indicates the engine control module has detected consistent misfires in cylinder 4. The 10th generation Civic offers multiple engine options.
2018 Civic Engine Options
The 2018 Civic offers the 2.0L naturally aspirated (158 hp), 1.5L turbocharged (174-180 hp), or 2.0L turbo Type R (306 hp). Cylinder 4 is the rearmost cylinder on all inline-4 configurations.
Common Causes
- Ignition Coil Failure: Age-related coil degradation
- Spark Plug Wear: May be due for replacement based on mileage
- Fuel Injector Issues: Direct injection deposits on turbo models
- Carbon Buildup: Common on 1.5L turbo at this age
- Vacuum Leaks: Gasket and hose deterioration
Diagnostic Approach
Use a Honda-compatible scanner for detailed diagnostics. At this age, component wear becomes more common. Test ignition components systematically. Check for carbon buildup on turbo models.
Repair Solutions
Replace aging ignition coils with quality parts. Install new spark plugs if at or past service interval. Address carbon buildup through professional cleaning. Repair vacuum leaks and deteriorated components.