Hummer H2 2004 Owner's Manual page 293

Tow/haul is designed to be most effective when the
vehicle and trailer combined weight is at least 75% 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. The
indicator light on the instrument panel will turn off.
The vehicle will automatically turn off tow/haul every
time it is started.
Driving with tow/haul 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.
A light on the instrument
panel will illuminate to
indicate that tow/haul
mode has been selected.
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