2003 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 513

Automatic Transmission Shift Lock Control System Check Ignition Transmission Lock Check . While parked, and with the parking brake set, try to turn the ignition key to LOCK in each shift lever position. e With an automatic transmission, the key should turn to LOCK only when the shift lever is in PARK (P). With a manual transmission, the key should turn to LOCK only when you press the key release button. e When you are doing this check, the vehicle could move suddenly. If it does, you or others could be injured. Follow the steps below. I On all vehicles, the key should come out only in LOCK. I 1. Before you start, be sure you have enough room around the vehicle. It should be parked on a level surface. 2. Firmly apply the parking brake. See Parking Brake on page 2-44 if necessary. Be ready to apply the regular brake immediately if the vehicle begins to move. 3. With the engine off, turn the key to the RUN position, but don't start the engine. Without applying the regular brake, try to move the shift lever out of PARK (P) with normal effort. If the shift lever moves out of PARK (P), your vehicle needs service. 6-14