2008 GMC Sierra 1500 Pickup Owner's Manual - Page 302

Tow/Haul may be turned off by pressing the switch again, at which time the indicator light on the instrument panel cluster will turn off. The vehicle will automatically turn off Tow/Haul every time it is started. Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the vehicle's Gross Combined Weight Rating (GCWR). See Weight of the Trailer later in this section. Tow/haul is most useful under the following driving conditions: Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/Haul is recommended only when pulling a heavy trailer or a large or heavy load. Weight of the Trailer How heavy can a trailer safely be? It depends on how you plan to use your rig. For example, speed, elevation, road grades, outside temperature and how much your vehicle is used to pull a trailer are all important. It can also depend on any special equipment that you have on your vehicle, and the amount of tongue weight the vehicle can carry. See "Weight of the Trailer Tongue" later in this section for more information. Maximum trailer weight is calculated assuming only the driver is in the tow vehicle and it has all the required trailering equipment. The weight of additional optional equipment, passengers and cargo in the tow vehicle must be subtracted from the maximum trailer weight. • When pulling a heavy trailer or a large or heavy load through rolling terrain. • When pulling a heavy trailer or a large or heavy load in stop and go traffic. • When pulling a heavy trailer or a large or heavy load in busy parking lots where improved low speed control of the vehicle is desired. Operating the vehicle in Tow/Haul when lightly loaded or with no trailer at all will not cause damage. However, there is no benefit to the selection of Tow/Haul when the vehicle is unloaded. 4-44