When your 2018 GMC Sierra displays diagnostic trouble code P0306, the engine control module has detected misfires in cylinder 6. The 2018 Sierra offers V6 and V8 engines, making P0306 a valid code on most configurations.
2018 Sierra Engine Options
The 2018 GMC Sierra 1500 offered the 4.3L V6, 5.3L V8, and 6.2L V8. All have six or more cylinders. V8 models feature Active Fuel Management (AFM) cylinder deactivation.
Age and Mileage Considerations
At 2018 age, wear-related issues are prominent. AFM lifter problems, worn spark plugs, degraded ignition coils, and fuel system issues are common at this mileage.
AFM System Issues
The 2018 Sierra's AFM system has known lifter wear issues. Cylinder 6 is part of the deactivation pattern and can develop lifter problems causing misfires.