GMC HUMMER EV 2023 Owner's Manual page 278

2. Adjust the Trailer Gain, using the Trailer
Gain adjustment buttons, to just below
the point of trailer wheel lockup,
indicated by trailer wheel squeal or tire
smoke when a trailer wheel locks. Trailer
wheel lockup 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.
3. Readjust Trailer Gain any time vehicle
loading, trailer loading, or road surface
conditions change or if trailer wheel
lockup is noticed at any time while
towing.
Other ITBC-Related DIC Messages
TRAILER BRAKES 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 vehicle 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 vehicle off.
3. Wait 10 seconds, then turn the vehicle
back to RUN.
4. If the CHECK TRAILER WIRING message
reappears, the electrical fault is on the
vehicle side.
Driving and Operating
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 BRAKES OR REDUCED
TRAILER BRAKING: This message will display
if the electric trailer brake performance is
either reduced or non-functional.
HOLD LAST KNOWN GAIN: This message will
display if it is no longer possible to adjust
the trailer brake gain. Trailer brakes may or
may not still be functional, and it is not
possible to adjust brake gain based on road
conditions. The trailer brakes may remain
functional until the next time the vehicle is
turned off.
TRAILER BRAKES DISABLED SERVICE
REQUIRED: This message will display when
there is a problem with the ITBC system.
If this message continues over multiple
restarts, have the vehicle serviced.
If the CHECK TRAILER WIRING, TRAILER
BRAKES DISABLED SERVICE REQUIRED,
SERVICE TRAILER BRAKE SYSTEM, or REDUCED
TRAILER BRAKING message displays while
driving, the ITBC system may not be fully
functional or may not function at all. When
traffic conditions allow, carefully pull the
vehicle over to the side of the road and turn
277