GMC 2011 Sierra Denali Owner's Manual page 342

9-90 Driving and Operating
2. There is an electrical fault in the
wiring to the electric 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 the driver
acknowledges this message.
To determine if the electrical fault is
on the vehicle side or trailer side of
the trailer wiring harness
connection, do the following:
1. Disconnect the trailer wiring
harness from the vehicle.
2. Turn the ignition to LOCK/OFF.
3. Wait 10 seconds, then turn the
ignition back to ON/RUN.
4. If the CHECK TRAILER WIRING
message re-appears, the
electrical fault is on the
vehicle side.
If the CHECK TRAILER WIRING
message only re-appears when
connecting the trailer wiring
harness to the vehicle, the
electrical fault is on the
trailer side.
SERVICE TRAILER BRAKE
SYSTEM: This message will be
displayed when there is a problem
with the ITBC system. If this
message persists over multiple
ignition cycles, there is problem with
the ITBC system. Take the vehicle
to an authorized GM dealer to have
the ITBC system diagnosed and
repaired.
If either the CHECK TRAILER
WIRING or SERVICE TRAILER
BRAKE SYSTEM message is
displayed while driving the
vehicle, power is no longer
available to the trailer brakes.
When traffic conditions allow,
carefully pull the vehicle over to the
side of the road and turn the ignition
off. Check the wiring connection to
the trailer and turn the ignition back
on. If either of these messages
continues, either the vehicle or
trailer needs service.
An authorized GM dealer may be
able to diagnose and repair
problems with the trailer. However,
any diagnosis and repair of the
trailer is not covered under the
vehicle warranty. Please contact
your trailer dealer for assistance
with trailer repairs and trailer
warranty information.