light GMC SIERRA 2007 Owner's Manual

The hitch should be located in the pickup bed so
that it’s centerline is over or slightly in front of the
rear axle. Take care that it is not so far forward that
it will contact the back of the cab in sharp turns.
This is especially important for short box pickups.
Trailer pin box extensions and sliding fth wheel
hitch assemblies can help this condition. There
should be at least six inches of clearance between
the top of the pickup box and the bottom of the
trailer shelf that extends over the box.
Make sure the hitch is attached to the tow vehicle
frame rails. Do not use the pickup box for support.
Safety Chains
You should always attach chains between your
vehicle and your trailer. Cross the safety chains
under the tongue of the trailer to help prevent the
tongue from contacting the road if it becomes
separated from the hitch. Instructions about safety
chains may be provided by the hitch manufacturer
or by the trailer manufacturer. If you are towing a
trailer up to 5,000 lbs (2 271 kg) with a
factory-installed step bumper, you may attach the
safety chains to the attaching points on the bumper.If you are towing a trailer up to your vehicle’s trailer
rating limit you may attach the safety chains to the
attaching point on the hitch platform. If you are
towing with an aftermarket hitch follow the trailer or
hitch manufacturer’s recommendation for attaching
safety chains. Always leave just enough slack so
you can turn with your rig. Never allow safety
chains to drag on the ground.
Trailer Brakes
If your trailer weighs more than 2,000 lbs (900 kg)
loaded, then it needs its own brakes – and they
must be adequate. Be sure to read and follow the
instructions for the trailer brakes so you’ll be
able to install, adjust and maintain them properly.
If your vehicle is equipped with StabiliTrak
®,
your trailer cannot tap into the vehicle’s hydraulic
brake system.
464

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 gearbefore
you 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 266.
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,
seeEngine Overheating on page 516.
475

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

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.
480

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

{CAUTION:
If a re starts while you are refueling, do
not remove the nozzle. Shut off the ow of
fuel by shutting off the pump or by
notifying the station attendant. Leave the
area immediately.
Notice:If you need a new fuel cap, be sure to
get the right type. Your dealer/retailer can
get one for you. If you get the wrong type, it
may not t properly. This may cause your
malfunction indicator lamp to light and may
damage your fuel tank and emissions system.
SeeMalfunction Indicator Lamp on page 260.
Filling a Portable Fuel Container
{CAUTION:
Never ll a portable fuel container while it
is in your vehicle. Static electricity
discharge from the container can ignite the
gasoline vapor. You can be badly burned
and your vehicle damaged if this occurs.
To help avoid injury to you and others:
Dispense gasoline only into approved
containers.
Do not ll a container while it is inside a
vehicle, in a vehicle’s trunk, pickup
bed, or on any surface other than the
ground.
Bring the ll nozzle in contact with the
inside of the ll opening before
operating the nozzle. Contact should
be maintained until the lling is
complete.
Do not smoke while pumping gasoline.
Do not use a cellular phone while
pumping gasoline.
495

Engine Oil (Gasoline Engine)
If your vehicle has a diesel engine, see “Engine
Oil” in the DURAMAX®Diesel Engine Supplement.
If the CHECK OIL LEVEL light appears on the
instrument cluster, except vehicles that have the
4.3L engine, check the engine oil level right away.
For more information, seeDriver Information
Center (DIC) on page 267. You should check the
engine oil level regularly; this is an added
reminder.
Checking Engine Oil
It is a good idea to check the engine oil every time
you get fuel. In order to get an accurate reading,
the oil must be warm and the vehicle must be
on level ground.
The engine oil dipstick handle is a yellow loop.
SeeEngine Compartment Overview on page 498
for the location of the engine oil dipstick.
1. Turn off the engine and give the oil several
minutes to drain back into the oil pan. If you
do not do this, the oil dipstick might not
show the actual level.
2. Pull out the dipstick and clean it with a paper
towel or cloth, then push it back in all the
way. Remove it again, keeping the tip down,
and check the level.
500

When to Inspect the Engine Air
Cleaner/Filter
If your vehicle has an air lter restriction indicator,
it lets you know when the engine air cleaner/lter
needs to be replaced. On vehicles with a restriction
indicator, you should inspect the air lter
restriction indicator at every oil change and
replace the engine air cleaner/lter when the
indicator tells you to.
On vehicles without an air lter restriction indicator,
inspect the air cleaner/lter at the MaintenanceII
intervals and replace it at the rst oil change
after each 50,000 mile (83 000 km) interval. See
Scheduled Maintenance (Gasoline Engine) on
page 623for more information. If you are driving
in dusty/dirty conditions, inspect the lter at
each engine oil change.
How to Inspect the Engine Air
Cleaner/Filter
Vehicles With an Air Filter Restriction
Indicator
Locate the air lter restriction indicator on the
engine air cleaner/lter cover. When the indicator
turns black or is in the red/orange “change”
zone, replace the lter and reset the indicator. See
Steps 1 through 7 to replace the engine air
cleaner/lter and to reset the air lter restriction
indicator.
Vehicles Without an Air Filter Restriction
Indicator
To inspect the air cleaner/lter, remove the engine
air cleaner/lter from the vehicle by following
Steps 1 through 7. When you have the engine air
cleaner/lter removed, lightly shake it to release
loose dust and dirt. If the engine air cleaner/lter
remains caked with dirt, a new lter is required.
506

Engine Coolant
If your vehicle has the DURAMAX®Diesel engine,
see the DURAMAX®Diesel manual for more
information.
The cooling system in your vehicle is lled with
DEX-COOL
®engine coolant. This coolant is
designed to remain in your vehicle for ve years or
150,000 miles (240 000 km), whichever occurs
rst, if you add only DEX-COOL
®extended
life coolant.
The following explains your cooling system and
how to add coolant when it is low. If you have
a problem with engine overheating, seeEngine
Overheating on page 516.A 50/50 mixture of clean, drinkable water and
DEX-COOL
®coolant will:
Give freezing protection down
to−34°F (−37°C).
Give boiling protection up to 265°F (129°C).
Protect against rust and corrosion.
Help keep the proper engine temperature.
Let the warning lights and gages work as
they should.
Notice:Using coolant other than DEX-COOL
®
may cause premature engine, heater core,
or radiator corrosion. In addition, the engine
coolant may require changing sooner, at
the rst maintenance service after each
30,000 miles (50 000 km) or 24 months,
whichever occurs rst. Any repairs would not
be covered by your warranty. Always use
DEX-COOL
®(silicate-free) coolant in your
vehicle.
513