GMC 2012 Sierra Denali Owner's Manual page 321

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. 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.
The vehicle may have an Integrated
Trailer Brake Control (ITBC) system
for electric trailer brakes.
This symbol is located on the Trailer
Brake Control Panel on vehicles
with an Integrated Trailer Brake
Control system. The power output to
the trailer brakes is based on the
amount of brake pressure being
applied by the vehicle s brake
system. This available power output
to the trailer brakes can be adjusted
to a wide range of trailering
situations.
The ITBC system is integrated with
the vehicle s brake, antilock brake,
and StabiliTrak systems. In trailering
conditions that cause the vehicle s
antilock brake or StabiliTrak
systems to activate, power sent to
the trailer's brakes will be
automatically adjusted to minimize
trailer wheel lock-up. This does not
imply that the trailer has the
StabiliTrak system.
Vehicles with StabiliTrak have a
Trailer Sway Control (TSC) feature.
See
Vehicles with StabiliTrak have a Hill
Start Assist (HSA) feature. See