2011 Chevrolet Silverado 2500 HD Extended Cab Owner's Manual - Page 445

Vehicle Care 10-39 Automatic Transmission Shift Lock Control Function Check 2. Firmly apply the parking brake. See Parking Brake on page 9‑64. Be ready to apply the regular brake immediately if the vehicle begins to move. 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. 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. . { 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. For automatic transmission vehicles, the ignition should turn to LOCK/OFF only when the shift lever is in P (Park). For manual transmission vehicles, the ignition should turn to LOCK/OFF only when you press the key release button. . On all vehicles, the ignition key should come out only in LOCK/OFF. Contact your dealer if service is required.