GMC SIERRA 2008 Owner's Manual

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 not enough 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 4-36for 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.
4. Adjust the Trailer Gain by using the gain adjustment
(+ /−) buttons on the Trailer Brake Control Panel.
5. Drive the vehicle with the trailer attached on a
level road surface representative of the towing
condition and free of traffic at about 20 to 25 mph
(32 to 40 km/h) and fully apply the Manual
Trailer Brake Apply lever.
Adjusting trailer gain at speeds lower than
20 to 25 mph (32 to 40 km/h) may result in an
incorrect gain setting.
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6. Adjust the Trailer Gain to just below the point of
trailer wheel lock-up, indicated by trailer wheel
squeal or puffs of tire smoke when a trailer
wheel locks.
Trailer wheel lock-up 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.
7. Re-adjust Trailer Gain any time vehicle loading,
trailer loading or road surface conditions change
or if you notice trailer wheel lock-up at any
time while you are towing
Other ITBC Related DIC Messages
In addition to displaying TRAILER GAIN and TRAILER
OUTPUT through the DIC, trailer connection and
ITBC system status is displayed in the DIC.
TRAILER CONNECTED – This message will be briey
displayed when a trailer with electric brakes is rst
connected to the vehicle. This message will
automatically turn off in about ten seconds. The driver
can also acknowledge this message before it
automatically turns off.CHECK TRAILER WIRING – This message will be
displayed if:
1. The ITBC system rst 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 thirty seconds. This message will also turn
off if the driver acknowledges this message off or if
the trailer harness is re-connected.
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.
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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.
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Driving with a Trailer
{CAUTION:
If you have a rear-most window open and you
pull a trailer with your vehicle, carbon
monoxide (CO) could come into your vehicle.
You cannot see or smell CO. It can cause
unconsciousness or death. SeeEngine
Exhaust on page 2-53. To maximize your safety
when towing a trailer:
Have your exhaust system inspected for
leaks, and make necessary repairs before
starting on your trip.
Keep the rear-most windows closed.
CAUTION: (Continued)
CAUTION: (Continued)

If exhaust does come into your vehicle
through a window in the rear or another
opening, drive with your front, main
heating or cooling system on and with the
fan on any speed. This will bring fresh,
outside air into your vehicle. Do not use
the climate control setting for maximum air
because it only recirculates the air inside
your vehicle. SeeClimate Control System
(With Air Conditioning ) on page 3-25or
Climate Control System (Heater Only) on
page 3-27.
Towing a trailer requires a certain amount of experience.
Before setting out for the open road, you’ll want to get
to know your rig. Acquaint yourself with the feel of
handling and braking with the added weight of the trailer.
And always keep in mind that the vehicle you are
driving is now a good deal longer and not nearly as
responsive as your vehicle is by itself.
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Before you start, check all trailer hitch parts and
attachments, safety chains, electrical connector, lamps,
tires and mirror adjustment. If the trailer has electric
brakes, start your vehicle and trailer moving and then
apply the trailer brake controller by hand to be sure
the brakes are working. This lets you check your
electrical connection at the same time.
During your trip, check occasionally to be sure that the
load is secure, and that the lamps and any trailer
brakes are still working.
While towing a trailer or when exposed to long periods
of sunshine, the oor of the truck bed may become
very warm. Avoid putting items in the truck bed
that might be affected by high ambient temperatures.
Following Distance
Stay at least twice as far behind the vehicle ahead as
you would when driving your vehicle without a trailer.
This can help you avoid situations that require
heavy braking and sudden turns.
Passing
You’ll need more passing distance up ahead when
you’re towing a trailer. And, because you’re a good deal
longer, you’ll need to go much farther beyond the
passed vehicle before you can return to your lane.
Backing Up
Hold the bottom of the steering wheel with one hand.
Then, to move the trailer to the left, just move that hand
to the left. To move the trailer to the right, move your
hand to the right. Always back up slowly and, if possible,
have someone guide you.
Making Turns
Notice:Making very sharp turns while trailering
could cause the trailer to come in contact with the
vehicle. Your vehicle could be damaged. Avoid
making very sharp turns while trailering.
When you’re turning with a trailer, make wider turns
than normal. Do this so your trailer won’t strike
soft shoulders, curbs, road signs, trees or other objects.
Avoid jerky or sudden maneuvers. Signal well in
advance.
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Turn Signals When Towing a Trailer
The arrows on your instrument panel will ash whenever
you signal a turn or lane change. Properly hooked up,
the trailer lamps will also ash, telling other drivers
you’re about to turn, change lanes or stop.
When towing a trailer, the arrows on your instrument
panel will ash for turns even if the bulbs on the trailer
are burned out. Thus, you may think drivers behind
you are seeing your signal when they are not. It’s
important to check occasionally to be sure the trailer
bulbs are still working.
Driving On Grades
Reduce speed and shift to a lower gearbeforeyou start
down a long or steep downgrade. If you don’t shift
down, you might have to use your brakes so much that
they would get hot and no longer work well.You can tow in DRIVE (D). You may want to shift the
transmission to lower gear selection if the transmission
shifts too often (e.g., under heavy loads and/or hilly
conditions).
You may also want to activate the tow/haul mode if the
transmission shifts too often. SeeTow/Haul Mode
Light on page 3-53.
When towing at high elevation on steep uphill grades,
consider the following: Engine coolant at higher
elevations will boil at a lower temperature than at or
near sea level. If you turn your engine off immediately
after towing at high elevation on steep uphill grades,
your vehicle may show signs similar to engine
overheating. To avoid this, let the engine run while
parked, preferably on level ground, with the transmission
in PARK (P) at least ve minutes before turning the
engine off. If you do get the overheat warning, see
Engine Overheating on page 5-30.
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Parking on Hills
{CAUTION:
You really should not park your vehicle, with a
trailer attached, on a hill. If something goes
wrong, your rig could start to move. People
can be injured, and both your vehicle and the
trailer can be damaged.
But if you ever have to park your rig on a hill, here’s
how to do it:
1. Apply your regular brakes, but don’t shift into
PARK (P) yet.
2. Have someone place chocks under the trailer
wheels.
3. When the wheel chocks are in place, release the
regular brakes until the chocks absorb the load.
4. Reapply the regular brakes. Then apply your
parking brake and shift into PARK (P).
5. If you have a four-wheel-drive vehicle, be sure the
transfer case is in a drive gear and not in
NEUTRAL.
6. Release the regular brakes.
{CAUTION:
It can be dangerous to get out of your vehicle
if the shift lever is not fully in PARK (P) with
the parking brake rmly set. Your vehicle
can roll.
If you have left the engine running, the vehicle
can move suddenly. You or others could be
injured. To be sure your vehicle will not move,
even when you are on fairly level ground, use
the steps that follow.
Always put the shift lever fully in PARK (P)
with the parking brake rmly set.
If the transfer case on four-wheel-drive vehicles
is in NEUTRAL, your vehicle will be free to roll,
even if your shift lever is in PARK (P). So, be
sure the transfer case is in a drive gear — not in
NEUTRAL.
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When You Are Ready to Leave After
Parking on a Hill
1. Apply your regular brakes and hold the pedal down
while you:
Start your engine
Shift into a gear
Release the parking brake
2. Let up on the brake pedal.
3. Drive slowly until the trailer is clear of the chocks.
4. Stop and have someone pick up and store the
chocks.
Maintenance When Trailer Towing
Your vehicle will need service more often when you’re
pulling a trailer. SeeScheduled Maintenance (Gasoline
Engine) on page 6-4for 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.
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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.
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Camper/Fifth-Wheel Trailer Wiring Package
The seven-wire camper harness is located under the
front edge of the pickup box on the driver’s side of the
vehicle, attached to the frame bracket. A connector
will have to be added to the wiring harness which
connects to the camper.
The harness contains the following camper/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 BrakeIf your vehicle is equipped with the “Heavy-Duty
Trailering” option, please refer to “Heavy-Duty Trailer
Wiring Package” earlier in this section.
When the camper-wiring harness is ordered without the
heavy-duty trailering package, an eight-wire harness
with a seven-pin connector is located at the rear of the
vehicle and is tied to the vehicle’s frame.
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