A P0304 diagnostic code on your 2021 Honda Pilot indicates the engine control module has detected repeated misfires in cylinder 4. The three-row SUV uses Honda's proven 3.5L V6 engine.
3.5L V6 Engine Layout
The 2021 Pilot uses the J35Y6 3.5L V6 producing 280 horsepower with Variable Cylinder Management (VCM). On this V6, cylinder 4 is on the rear bank. VCM can add complexity to misfire diagnosis.
Common Causes
- Ignition Coil Failure: Individual coil-on-plug units can fail
- Spark Plug Wear: Honda recommends specific iridium plugs
- VCM System Issues: Cylinder deactivation components can cause misfires
- Fuel Injector Problems: Direct injection deposits
- Carbon Buildup: GDI technology leads to intake valve deposits
Diagnostic Approach
Use a Honda-compatible scanner for V6-specific diagnostics. Monitor VCM operation and misfire correlation. Test ignition components systematically. Check for carbon buildup symptoms.
Repair Solutions
Replace failed ignition coils with Honda OEM components. Install properly specified spark plugs. Address VCM-related issues through dealer diagnosis. Consider carbon cleaning at higher mileages.