The 2021 Toyota Highlander V6 features the 3.5L 2GR-FKS engine with D-4S dual injection, producing 295 horsepower for confident family hauling. When P0306: Cylinder 6 Misfire Detected triggers your check engine light, your Highlander's engine management has identified combustion problems specifically in cylinder 6.
V6 Engine Configuration
Toyota's 3.5L V6 positions cylinder 6 on the rear bank near the firewall, where reduced airflow creates elevated operating temperatures. The D-4S dual injection system combines direct injection efficiency with port injection's intake valve cleaning benefits, helping reduce carbon buildup compared to direct-injection-only engines.
Common P0306 Causes
Heat-stressed ignition coils fail more frequently on rear-bank cylinders. Spark plugs exceeding service intervals produce weak or erratic spark. Despite D-4S benefits, some carbon accumulation occurs over time. Fuel injector issues—either direct or port—affect proper fuel delivery. Vacuum leaks near the rear intake runners create lean conditions.
Systematic Diagnosis
Scan for all codes to understand the complete diagnostic picture. Access the rear cylinder bank and inspect cylinder 6's ignition coil for heat damage, cracks, or connector corrosion. Remove the spark plug and examine electrode condition and gap. Test both direct and port fuel injector operation. Perform compression testing to verify cylinder 6's mechanical integrity. Check for intake vacuum leaks.
D-4S Technology Advantages
The Highlander V6's dual injection helps prevent severe carbon buildup common in other modern engines. Port injection during cold starts and light loads cleans intake valves, reducing one major misfire cause.