2008 Hummer H2 Owner's Manual - Page 325

Tow/Haul mode is most effective when the vehicle and trailer combined weight is at least 75 percent of the vehicle's Gross Combination Weight Rating (GCWR). See "Weight of the Trailer" later in this section. Press the button on the instrument panel to the right of the steering wheel to enable the tow/haul mode. Press the button again to turn off Tow/Haul mode. The indicator light on the instrument panel will turn off. The vehicle will automatically turn off Tow/Haul mode every time it is started. Driving with Tow/Haul mode activated without a heavy load or with no trailer will cause reduced fuel economy and unpleasant engine and transmission driving characteristics, but will not cause damage. Grade Braking Transmission Grade Braking works in Tow/Haul mode to automatically downshift the transmission when the driver is braking. The purpose is to aid in braking or maintaining vehicle speeds on down-grades by shifting to a lower gear to utilize engine braking. A light on the instrument panel will illuminate to indicate that tow/haul mode has been selected. 4-57