The P0304 diagnostic trouble code on your 2020 Toyota 4Runner indicates the engine control module has detected consistent misfires in cylinder 4. The fifth-generation 4Runner uses the proven 4.0L V6 engine.
4.0L V6 Engine Layout
The 2020 4Runner uses the 1GR-FE 4.0L V6 producing 270 horsepower with port fuel injection. Cylinder 4 is located on the driver's side (left) bank of this V6. This proven engine is known for exceptional reliability.
Common Causes
- Ignition Coil Failure: Individual coil-on-plug units can fail
- Spark Plug Wear: Iridium plugs eventually need replacement
- Fuel Injector Problems: Port injection deposits
- Vacuum Leaks: Intake manifold or gasket failures
- Air Injection System: Secondary air system issues
Diagnostic Approach
Use a Toyota-compatible scanner for V6 diagnostics. Port injection is simple and reliable. Monitor misfire counts across all six cylinders. Test ignition components systematically.
Repair Solutions
Replace failed ignition coils with Denso OEM components. Install Toyota-specified iridium spark plugs. Clean fuel injectors if needed. Repair vacuum and air injection system leaks.