2012 GMC Sierra Owner's Manual - Page 311

Driving and Operating 9-35 Automatic Transmission If the vehicle is a hybrid, see the hybrid supplement for more information. Vehicles with an automatic transmission have an electronic shift position indicator within the instrument panel cluster. This display comes on when the ignition key is turned to the ON/RUN position. There are several different positions for the shift lever. Heavy Duty 6-Speed Automatic Transmission Shown (Light Duty 6‐Speed Similar) See "Range Selection Mode" under Manual Mode on page 9‑38. P (Park): This position locks the rear wheels. It is the best position to use when starting the engine because the vehicle cannot move easily. When parked on a hill, especially when the vehicle has a heavy load, you might notice an increase in the effort to shift out of P (Park). See "Torque Lock" under Shifting Into Park on page 9‑30 for more information. { WARNING It is dangerous to get out of the vehicle if the shift lever is not fully in P (Park) with the parking brake firmly set. The vehicle can roll. Do not leave the vehicle when the engine is running unless you have to. If you have left the engine running, the vehicle can move suddenly. You or others could be injured. To be sure the vehicle will not move, even when you are on fairly level ground, always set the parking brake and move the shift lever to P (Park). See Shifting Into Park on page 9‑30. If you are pulling a trailer, see Driving Characteristics and Towing Tips on page 9‑74. Hydra-Matic® 4-Speed Automatic Transmission