GMC Yukon 2012 Owner's Manual page 361

There is a fault present in the
wiring to the electric trailer
brakes (a CHECK TRAILER
WIRING message will also be
displayed on the DIC).
There is a fault in the ITBC
system (a SERVICE TRAILER
BRAKE SYSTEM message will
also be displayed in the DIC).
Manual Trailer Brake Apply
The Manual Trailer Brake Apply
Lever is located on the Trailer Brake
Control Panel and is used to apply
the trailer s electric brakes
independent of the vehicle s brakes.
This lever is used in the Trailer Gain
Adjustment Procedure to properly
adjust the power output to the trailer
brakes. Sliding the lever to the left
will apply only the trailer brakes.
The power output to the trailer is
indicated in the Trailer Brake
Display Page in the DIC.
If the vehicle s service brakes are
applied while using the Manual
Trailer Brake Apply Lever, the trailer
output power will be the greater of
the two.
The trailer and the vehicle's brake
lamps will come on when either
vehicle braking or manual trailer
brakes are applied.
Trailer Gain Adjustment Procedure
Trailer Gain should be set for a
specific trailering condition and must
be adjusted any time vehicle
loading, trailer loading or road
surface conditions change.
Setting the Trailer Gain properly is
needed for the best trailer stopping
performance. A trailer that is
over-gained may result in locked
trailer brakes. A trailer that is
under-gained may result in not
enough trailer braking. Both of these
conditions may result in poorer
stopping and stability of the vehicle
and trailer.
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
display.
The Trailer Brake Display
Page will appear on the
DIC showing TRAILER
GAIN and TRAILER
OUTPUT.
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