2007 GMC SIERRA service

Trailer Brake DIC Display Page
The ITBC system displays messages into the
vehicle’s Driver Information Center (DIC). SeeDIC
Warnings and Messages on page 279for more
information.
The display page indicates Trailer Gain setting,
power output to the electric trailer brakes, trailer
connection and system operational status.
A. Trailer Gain Setting
B. Power Output to Trailer Brakes
C. No trailer with electric brakes connected or fault
presentThe Trailer Brake Display Page can be displayed
by performing any of the following actions:
Scrolling through the DIC menu pages using
the odometer trip stem or the DIC Vehicle
Information button (if equipped).
Pressing a Trailer Gain button – If the Trailer
Brake Display Page is not currently displayed,
pressing a Trailer Gain button will rst
recall the current Trailer Gain setting. After the
Trailer Brake Display Page is displayed,
subsequent depressions of the gain buttons
will then cause the Trailer Gain setting to
change.
Activating the Manual Trailer Brake Apply
lever
Connecting a trailer equipped with electric
trailer brakes
All DIC warning and service messages must rst
be acknowledged by the driver before the
Trailer Brake Display Page can be displayed and
Trailer Gain can be adjusted.
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TRAILER GAIN – This setting is displayed
anytime the Trailer Brake Display Page is active.
This setting can be adjusted from 0.0 to 10.0
with either a trailer connected or disconnected. To
adjust the Trailer Gain, press one of the Trailer
Gain adjustment buttons located on the Trailer
Brake Control Panel. Pressg and hold a gain
button to cause the Trailer Gain to continuously
adjust. To turn the output to the trailer off,
adjust the Trailer Gain setting to 0.0 (zero).
0.0 (zero) gain is the factory default setting. To
properly adjust trailer gain, see the Trailer
Gain Adjustment Procedure later in this section.
TRAILER OUTPUT – This is displayed any time a
trailer with electric brakes is connected. Output
to the electric brakes is based on the amount
of vehicle braking present and relative to
the Trailer Gain setting. Output is displayed from 0
to 10 bars for each gain setting.The Trailer Output will indicate “------“onthe
Trailer Brake Display Page whenever the following
occur:
No trailer is connected.
A trailer without electric brakes is connected
(no DIC message is displayed).
A trailer with electric brakes has become
disconnected (a CHECK TRAILER WIRING
message will also be displayed on the DIC).
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).
469

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 your
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 your 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 specic 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 notenough trailer braking. Both of these conditions
may result in poorer stopping and stability of
the vehicle and trailer.
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. SeeLoading Your
Vehicle on page 425for more information.
3. After the electrical connection is made to a
trailer equipped with electric brakes:
A TRAILER CONNECTED message will be
briey displayed on the DIC display.
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.
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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 the driver acknowledges this message
off or if the trailer harness is re-connected.
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 off.
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 OFF.
3. Wait ten seconds, then turn the ignition back
to 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 you connect 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 your 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 you are driving your vehicle, you no
longer have power available to your trailer brakes.
When traffic conditions allow, carefully pull your
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 your vehicle or your
trailer needs service.
An authorized GM dealer may be able to diagnose
and repair problems with your trailer. However, any
diagnosis and repair of your trailer is not covered
under your GM Warranty. Please contact your
trailer dealer for assistance with trailer repairs and
trailer warranty information.
472

Maintenance When Trailer Towing
Your vehicle will need service more often when
you’re pulling a trailer. SeeScheduled
Maintenance (Gasoline Engine) on page 623for
more information. Things that are especially
important in trailer operation are automatic
transmission uid (don’t overll), engine oil, axle
lubricant, belt, cooling system and brake system.
Each of these is covered in this manual, and
the Index will help you nd them quickly. If you’re
trailering, it’s a good idea to review these
sections before you start your trip.
Check periodically to see that all hitch nuts and
bolts are tight.
Trailer Wiring Harness
Your vehicle is equipped with one of the following
wiring harnesses for towing a trailer or hauling
a slide-in camper.
Basic Trailer Wiring
All regular, extended cab and crew cab pickups
have a seven-wire trailer towing harness.
For vehicles not equipped with heavy duty
trailering, the harness is clipped to the vehicle’s
frame behind the spare tire mount. The harness
requires the installation of a trailer connector,
which is available through your dealer.
If you need to tow a light-duty trailer with a
standard four-way round pin connector, you can
also get an adapter from your dealer.
478

Heavy-DutyTrailer Wiring Harness
Package
For vehicles equipped with heavy duty trailering,
the harness is connected to a bracket on the hitch
platform. The seven-wire harness contains the
following trailer circuits:
Yellow: Left Stop/Turn Signal
Dark Green: Right Stop/Turn Signal
Brown: Taillamps
White: Ground
Light Green: Back-up Lamps
Red: Battery Feed*
Dark Blue: Trailer Brake**The fuses for these two circuits are installed in
the underhood electrical center, but the wires
are not connected. They should be connected by
your dealer or a qualied service center. The
fuse and wire for the ITBC is factory installed and
connected if the vehicle is equipped with an
ITBC. The fuse for the battery feed is not required
if your vehicle has an auxiliary battery. If your
vehicle does not have an auxiliary battery, have
your dealer or authorized service center install the
required fuse.
If you are charging a remote (non-vehicle) battery,
press the tow/haul mode button located at the
end of the shift lever. This will boost the vehicle
system voltage and properly charge the battery. If
the trailer is too light for tow/haul mode, you
can turn on the headlamps as a second way to
boost the vehicle system and charge the battery.
479

Electric Brake Control Wiring
Provisions
These wiring provisions are included with your
vehicle as part of the trailer wiring package. These
provisions are for an electric brake controller.
The instrument panel contains blunt cut wires near
the data link connector for the trailer brake
controller. The harness contains the following
wires:
Dark Blue: Brake Signal to Trailer Connector
Red/Black: Battery
Light Blue/White: Brake Switch
White: GroundIt should be installed by your dealer or a qualied
service center.
If your vehicle is equipped with an ITBC, the blunt
cuts exist, but are not connected further in the
harness. If you install an aftermarket trailer brake
controller, the ITBC must be disconnected. Do
not power both ITBC and aftermarket controllers to
control the trailer brakes at the same time.
Auxiliary Battery
The auxiliary battery provision can be used to
supply electrical power to additional equipment that
you may choose to add, such as a slide-in
camper. If your vehicle has this provision, this
relay will be located on the driver’s side of
the vehicle, next to the underhood electrical center.
481

Service........................................................ 486
Accessories and Modications................... 486
California Proposition 65 Warning.............. 487
Doing Your Own Service Work.................. 487
Adding Equipment to the Outside of
Your Vehicle.......................................... 488
Fuel............................................................. 488
Gasoline Octane........................................ 489
Gasoline Specications.............................. 489
California Fuel........................................... 489
Additives................................................... 490
Fuel E85 (85% Ethanol)............................ 491
Fuels in Foreign Countries........................ 492
Filling the Tank......................................... 493
Filling a Portable Fuel Container............... 495
Checking Things Under the Hood.............. 496
Hood Release........................................... 497
Engine Compartment Overview.................. 498
Engine Oil (Gasoline Engine).................... 500
Engine Oil Life System.............................. 503
Engine Air Cleaner/Filter
(Gasoline Engines)................................. 505Automatic Transmission Fluid.................... 508
Engine Coolant.......................................... 513
Coolant Surge Tank Pressure Cap............ 516
Engine Overheating................................... 516
Overheated Engine Protection Operating
Mode (V8 Engines Only)........................ 519
Cooling System......................................... 520
Engine Fan Noise..................................... 525
Power Steering Fluid................................. 526
Windshield Washer Fluid........................... 527
Brakes...................................................... 528
Battery...................................................... 531
Jump Starting............................................ 532
Rear Axle.................................................... 538
Four-Wheel Drive........................................ 539
Front Axle................................................... 541
Noise Control System................................. 542
Tampering with Noise Control System
Prohibited.............................................. 542
Section 5 Service and Appearance Care
483