2007 GMC SIERRA CLASSIC towing

Towing a Trailer
Do not tow a trailer during break-in. SeeNew
Vehicle Break-In on page 134for more information.
{CAUTION:
If you do not use the correct equipment
and drive properly, you can lose control
when you pull a trailer. For example, if the
trailer is too heavy, the brakes may not
work well — or even at all. You and your
passengers could be seriously injured.
Pull a trailer only if you have followed all
the steps in this section. Ask your dealer
for advice and information about towing a
trailer with your vehicle.Notice:Pulling a trailer improperly can
damage your vehicle and result in costly
repairs not covered by your warranty.
To pull a trailer correctly, follow the advice in
this part, and see your dealer for important
information about towing a trailer with
your vehicle.
To identify the trailering capacity of your vehicle,
you should read the information in “Weight of
the Trailer” that appears later in this section.
Trailering is different than just driving your vehicle
by itself. Trailering means changes in acceleration,
braking, handling, durability and fuel economy.
Successful, safe trailering takes correct equipment,
and it has to be used properly.
That’s the reason for this part. In it are many
time-tested, important trailering tips and safety
rules. Many of these are important for your safety
and that of your passengers. So please read
this section carefully before you pull a trailer.
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If You Do Decide To Pull A Trailer
If you do, here are some important points:
There are many different laws, including speed
limit restrictions, having to do with trailering.
Make sure your rig will be legal, not only where
you live but also where you’ll be driving.
A good source for this information can be state
or provincial police.
Consider using a sway control. See “Hitches”
later in this section.
Don’t tow a trailer at all during the rst
500 miles (800 km) your new vehicle is driven.
Your engine, axle or other parts could be
damaged.
Then, during the rst 500 miles (800 km) that
you tow a trailer, don’t drive over 50 mph
(80 km/h) and don’t make starts at full throttle.
This helps your engine and other parts of
your vehicle wear in at the heavier loads.
If you have an automatic transmission, you
can tow in DRIVE (D). You may want to
shift the transmission to THIRD (3) or, if
necessary, a lower gear selection if the
transmission shifts too often, such as under
heavy loads and/or hilly conditions. If you have
a manual transmission and you are towing a
trailer, it’s better not to use the highest
gear. SeeTow/Haul Mode Light on page 264.
Three important considerations have to do
with weight:
The weight of the trailer
The weight of the trailer tongue
The weight on your vehicle’s tires
Tow/Haul Mode
Tow/Haul is a feature on automatic transmission
equipped vehicles that assists when pulling a heavy
trailer or a large or heavy load. SeeTow/Haul Mode
on page 147for more information.
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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 aretowing 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.
Your trailer brake system can tap into the
vehicle’s hydraulic brake system only if:
The trailer parts can withstand 3,000 psi
(20 650 kPa) of pressure.
The trailer’s brake system will use less than
0.02 cubic inch (0.3 cc) of uid from your
vehicle’s master cylinder. Otherwise,
both braking systems won’t work well. You
could even lose your brakes.
If everything checks out this far, make the brake tap
at the port on the master cylinder that sends the
uid to the rear brakes. But don’t use copper tubing
for this. If you do, it will bend and nally break off.
Use steel brake tubing.
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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. See
Engine Exhaust on page 174. 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
on page 230.
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 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.
If you have an automatic transmission, 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 264.
If you have a 5-speed manual transmission and
you are towing a trailer, it’s better not to use
FIFTH (5) gear. Just drive in FOURTH (4) gear
(or, as you need to, a lower gear).
When towing at high altitude on steep uphill
grades, consider the following: Engine coolant at
or near sea level will boil at a lower temperature
than at higher altitudes. If you turn your engine off
immediately after towing at high altitude 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 automatic transmission in
PARK (P) for a few minutes before turning
the engine off. For manual transmissions, let the
engine run while parked, preferably on level
ground, with the transmission out of gear and the
parking brake applied, for a few minutes before
turning the engine off. If you do get the overheat
warning, seeEngine Overheating on page 505.
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Maintenance When Trailer Towing
Your vehicle will need service more often when
you’re pulling a trailer. SeeScheduled
Maintenance (Gasoline Engine) on page 617for
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 an eight-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 your trailer is equipped with electric brakes, you
can get a jumper harness (electric trailer brake
control) with a trailer battery feed fuse from
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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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
passenger’s side of the
vehicle, next to the
auxiliary battery.
When using this provision, connection should only
be made to the upper stud (A) of the relay. Do not
make connections to the lower stud (B) of the relay.
The auxiliary battery circuit is protected by a
megafuse located behind the auxiliary battery.
Be sure to follow the proper installation instructions
that are included with any electrical equipment
that you install.Notice:Leaving electrical equipment on for
extended periods will drain the battery. Always
turn off electrical equipment when not in
use and do not use equipment that exceeds
the maximum amperage rating for the auxiliary
battery provision.
Power Winches
If you wish to use a power winch on your vehicle,
only use it when your vehicle is stationary or
anchored.
Trailer Recommendations
You must subtract your hitch loads from the CWR
for your vehicle. Weigh your vehicle with the
trailer attached, so that you won’t go over
the GVWR or GAWR. If you are using a
weight-distributing hitch, weigh the vehicle without
the spring bars in place.
You’ll get the best performance if you spread out
the weight of your load the right way, and if
you choose the correct hitch and trailer brakes.
For more information, seeTowing a Trailer
on page 429.
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