GMC Sierra 2500 HD2022 Owner's Manual page 291

290 Driving and Operating
To adjust Trailer Gain for each towing
condition:
1. Drive the vehicle with the trailer
attached on a level road surface
representative of the towing condition
and free of traffic at about 32 40 km/h
(20 25 mph) and fully apply the Manual
Trailer Brake Apply Lever.
Adjusting Trailer Gain at speeds lower
than 32 40 km/h (20 25 mph) may
result in an incorrect gain setting.
2. Adjust the Trailer Gain, using the Trailer
Gain (+) or ( ) adjustment buttons, 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. Adjust
the Trailer Gain to the highest allowable
setting for the towing condition.
3. Readjust Trailer Gain anytime vehicle
loading, trailer loading, or road surface
conditions change or if trailer wheel
lock-up is noticed at any time while
towing.
Other ITBC-Related DIC Messages
TRAILER CONNECTED: This message will
briefly display when a trailer with electric
brakes is first connected to the vehicle. This
message will automatically turn off in about
10 seconds. This message can be
acknowledged before it automatically
turns off.
CHECK TRAILER WIRING: This message will
display if:
The ITBC system first determines
connection to a trailer with electric brakes
and then the trailer harness becomes
disconnected from the vehicle.
If the disconnect occurs while the vehicle
is stationary, this message will
automatically turn off in about
30 seconds. This message will also turn
off if it is acknowledged or if the trailer
harness is reconnected.
If the disconnect occurs while the vehicle
is moving, this message will continue
until the ignition is turned off. This
message will also turn off if it is
acknowledged or if the trailer harness is
reconnected.
There is an electrical fault in the wiring to
the trailer brakes. This message will
continue as long as there is an electrical
fault in the trailer wiring. This message
will also turn off if it is acknowledged.
To determine whether the electrical fault is
on the vehicle side or trailer side of the
trailer wiring harness connection:
1. Disconnect the trailer wiring harness
from the vehicle.
2. Turn the ignition off.
3. Wait 10 seconds, then turn the ignition
back to RUN.
4. If the CHECK TRAILER WIRING message
reappears, the electrical fault is on the
vehicle side.
If the CHECK TRAILER WIRING message only
reappears when connecting the trailer wiring
harness to the vehicle, the electrical fault is
on the trailer side.
SERVICE TRAILER BRAKE SYSTEM: This
message will display when there is a
problem with the ITBC system. If this
message continues over multiple ignition
cycles, have the vehicle serviced.