2003 GMC Sonoma Owner's Manual - Page 108

Leaving Your Vehicle With the Engine Running Move the lever up as far as it will go. It can be dangerous to leave your vehicle with the engine running. Your vehicle could move suddenly if the shift lever is not fully in PARK (P) with the parking brake firmly set. And, if you leave the vehicle with the engine running, it could overheat and even catch fire. You or others could be injured. Don't leave your vehicle with the engine running. 3. Turn the ignition key to LOCK. 4. Remove the key and take it with you. If you can leave your vehicle with the key, your vehicle is in PARK (P). If you have to leave your vehicle with the engine running, be sure your vehicle is in PARK (P) and your parking brake is firmly set before you leave it. After you've moved the shift lever into PARK (P), hold the regular brake pedal down. Then, see if you can move the shift lever away from PARK (P) without first pulling it toward you. If you can, it means that the shift lever wasn't fully locked into PARK (P). 2-33