2012 GMC Sierra Owner's Manual - Page 306

9-30 Driving and Operating wire tie which bundles the electrical plug. Do not cut the electrical cord. 3. Plug the cord into a normal, grounded 110-volt AC outlet. The length of time the heater should remain plugged in depends on several factors. Ask a dealer in the area where you will be parking the vehicle for the best advice on this. Engine Coolant Heater The engine heater can provide easier starting and better fuel economy during engine warm-up in cold weather conditions at or below −18°C (0°F). Vehicles with an engine heater should be plugged in at least four hours before starting. An internal thermostat in the plug-end of the cord may exist which will prevent engine coolant heater operation at temperatures above −18°C (0°F). If the vehicle has a diesel engine, see the Duramax Diesel supplement for more information. { WARNING Plugging the cord into an ungrounded outlet could cause an electrical shock. Also, the wrong kind of extension cord could overheat and cause a fire. You could be seriously injured. Plug the cord into a properly grounded three-prong 110-volt AC outlet. If the cord will not reach, use a heavy-duty three-prong extension cord rated for at least 15 amps. 4. Before starting the engine, be sure to unplug and store the cord as it was before to keep it away from moving engine parts. If you do not, it could be damaged. Shifting Into Park { WARNING It can be 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. 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, use the steps that follow. With four-wheel drive, if the transfer case is in N (Neutral), the vehicle will be free to roll, even if the shift lever is in P (Park). So, be sure the transfer case is in a drive (Continued) To Use the Engine Coolant Heater 1. Turn off the engine. 2. Open the hood and unwrap the electrical cord. The cord is secured to the Engine Compartment Fuse Block with a clip. Carefully remove the