The 2018 GMC Sierra 1500 represents the final year of the K2XX generation, offering the 4.3-liter V6, 5.3-liter V8, and 6.2-liter V8 engines. All configurations include cylinder 5 as a legitimate cylinder position. A P0305 diagnostic trouble code indicates misfire detection at this cylinder.
Understanding P0305 on 2018 Sierra
The P0305 code signifies "Cylinder 5 Misfire Detected." On GM V6 and V8 engines, cylinder 5 is on the driver's side bank. The K2XX generation V8s feature Active Fuel Management (AFM) cylinder deactivation where cylinder 5 is one of the deactivating cylinders.
AFM System and Lifter Failures
The 2018 Sierra's 5.3L and 6.2L V8s use AFM with cylinders 1, 4, 6, and 7 deactivating (not cylinder 5 on most configurations). However, AFM lifter failures can affect any cylinder and cause misfires. At the 2018 model year age, lifter wear becomes increasingly relevant.
Age-Related Considerations
Vehicles of this vintage may have accumulated significant mileage. Spark plugs, ignition coils, and fuel injectors can all degrade. Carbon buildup on direct injection engines (5.3L DI variant) becomes more significant with age.
4.3L V6 Diagnosis
The 4.3L V6 doesn't use AFM, providing simpler diagnosis. Traditional misfire causes including ignition components, fuel delivery, and mechanical issues should be evaluated for cylinder 5.