2004 GMC Savana Van Owner's Manual - Page 235

Press this button located to the right of the steering wheel on the instrument panel to turn tow/haul mode on and off. Tow/haul mode will turn off automatically when the ignition is turned off. See Tow/Haul Mode Light on page 3-36. Tow/haul is most effective when the vehicle and trailer combined weight is at least 75% of the vehicle's Gross Combined Weight Rating (GCWR). See "Weight of the Trailer" later in this section. Driving with tow/haul activated without a heavy load will cause reduced fuel economy and unpleasant engine and transmission driving characteristics, but will not cause damage. While activated, the indicator light on the instrument panel will be on. Weight of the Trailer How heavy can a trailer safely be? It depends on how you plan to use your rig. For example, speed, altitude, road grades, outside temperature and how much your vehicle is used to pull a trailer are all important. And, it can also depend on any special equipment that you have on your vehicle. 4-39