GMC 2012 Sierra Denali Owner's Manual page 334

9-84 Driving and Operating
Use the following procedure to
correctly adjust Trailer Gain for each
towing condition:
1. Make sure the trailer brakes are
in proper working condition.
2. Connect a properly loaded trailer
to the vehicle and make all
necessary mechanical and
electrical connections. See
Vehicle Load Limits on
page 9 16 for more information.
3. After the electrical connection is
made to a trailer equipped with
electric brakes:
A TRAILER CONNECTED
message will be briefly
displayed on the DIC.
The Trailer Brake Display
Page will appear on the
DIC showing TRAILER
GAIN and TRAILER
OUTPUT.
In the Trailer Output Display
on the DIC, - - - - - - will
disappear if there is no
error present. Connecting a
trailer without electric
brakes will not clear the six
dashed lines.
4. Adjust the Trailer Gain by using
the gain adjustment (+ / -)
buttons on the Trailer Brake
Control Panel.
5. Drive the vehicle with the trailer
attached on a level road surface
representative of the towing
condition and free of traffic at
about 32 to 40 km/h (20 to
25 mph) and fully apply the
Manual Trailer Brake Apply
Lever.
Adjusting trailer gain at speeds
lower than 32 to 40 km/h (20 to
25 mph) may result in an
incorrect gain setting.
6. Adjust the Trailer Gain to just
below the point of trailer wheel
lock-up, indicated by trailer
wheel squeal or tire smoke when
a trailer wheel locks.
Trailer wheel lock-up may not
occur if towing a heavily loaded
trailer. In this case, adjust the
Trailer Gain to the highest
allowable setting for the towing
condition.
7. Re-adjust Trailer Gain any time
vehicle loading, trailer loading,
or road surface conditions
change or if trailer wheel lock-up
is noticed at any time while
towing.