2012 GMC Sierra Owner's Manual - Page 421

Vehicle Care 10-35 Starter Switch Check { WARNING When you are doing this inspection, the vehicle could move suddenly. If the vehicle moves, you or others could be injured. 1. Before starting this check, be sure there is enough room around the vehicle. 2. Firmly apply both the parking brake and the regular brake. See Parking Brake on page 9‑54. Do not use the accelerator pedal, and be ready to turn off the engine immediately if it starts. 3. Try to start the engine in each gear. The vehicle should start only in P (Park) or N (Neutral). If the vehicle starts in any other position, contact your dealer for service. Automatic Transmission Shift Lock Control Function Check 3. With the engine off, turn the ignition on, but do not start the engine. Without applying the regular brake, try to move the shift lever out of P (Park) with normal effort. If the shift lever moves out of P (Park), contact your dealer for service. { WARNING When you are doing this inspection, the vehicle could move suddenly. If the vehicle moves, you or others could be injured. 1. Before starting this check, be sure there is enough room around the vehicle. It should be parked on a level surface. 2. Firmly apply the parking brake. See Parking Brake on page 9‑54. Be ready to apply the regular brake immediately if the vehicle begins to move. Ignition Transmission Lock Check While parked, and with the parking brake set, try to turn the ignition to LOCK/OFF in each shift lever position. . The ignition should turn to LOCK/OFF only when the shift lever is in P (Park). The ignition key should come out only in LOCK/OFF. . Contact your dealer if service is required.