trailer GMC SIERRA DENALI 2003 Owner's Manual

Safety Chains
You should always attach safety 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.
You may attach the safety chains to the attaching point
on the hitch platform. 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 Ibs. (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:
(20 650 kPa) of pressure.
The trailer parts can withstand 3,000 psi
The trailer’s brake system will use less than
0.02 cubic inch (0.3 cc) of fluid 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 fluid
to the rear brakes. But don’t use copper tubing for this.
If you do, it will bend and finally break off. Use steel
brake tubing.
Driving with a Trailer
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.
Before you start, check the trailer hitch and platform
(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 floor of the truck bed may become
very warm. Avoid putting items in the truck bed
that might be affected by high ambient temperatures.
4-56

Making Turns
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.
Your vehicle is equipped with four-wheel steering and
if
you use it while backing your trailer the same rules
apply. However, with four-wheel steering your rig will
respond more quickly and it may take additional practice
to get used to backing up with four-wheel steering.
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.
Turn Signals When Towing a Trailer
The arrows on your instrument panel will flash whenever
you signal a turn or lane change. Properly hooked up,
the trailer lamps will also flash, telling other drivers
you’re about to turn, change lanes or stop.
When towing a trailer, the arrows on your instrument
panel will flash 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.
4-57

Driving On Grades
Reduce speed and shift to a lower gear before 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
(5). You may want to shift the
transmission to THIRD
(3) or, if necessary, a 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. See “Tow/Haul Mode”
earlier in this section.
When towing at high altitude on steep uphill grades,
consider the following: Engine coolant will boil at a lower
temperature than at normal 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. If you do get
the overheat warning, see
Engine Overheating on
page
5-27.
Parking on Hills
m
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. Release the regular brakes.
4-58

When You Are Ready to Leave After
Parking on a
Hill
1. Apply your regular brakes and hold the pedal down
while you:
0 start your engine,
shift into a gear, and
0 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. See the Maintenance Schedule for more
on this. Things that are especially important in trailer
operation are automatic transmission fluid (don’t overfill),
engine
oil, axle lubricant, belt, cooling system and
brake system. Each of these is covered in this manual,
and the Index will help you find 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.
4-59

Trailer Wiring Harness
Your pickup is equipped with the eight-wire trailer
towing harness. This harness with a seven-pin universa
heavy-duty trailer connector is attached to a bracket
on the hitch platform.
The Center High-Mounted Stoplamp (CHMSL) wire is
tied next to the trailer wiring harness for use with a
trailer, slide-in camper or cap. The
eight-wire harness contains the following trailer
circuits:
Yellow: Left Stopnurn Signal
Dark Green: Right Stopnurn Signal
Brown: Taillamps
White: Ground
Light Green: Back-up Lamps
Light Blue: Center High-Mounted Stoplamp
(CHMSL)
Red: Battery Feed
Dark Blue: Trailer Brake
If your trailer
is equipped with electrical brakes, you can
get a jumper harnesdelectric trailer brake control
with a trailer battery feed fuse from your dealer. This
harness and fuse should be installed by your dealer or a
qualified service center.
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.
4-60

Automatic Transmission Fluid
When to Check and Change
A good time to check your automatic transmission fluid
level
is when the engine oil is changed.
Change both the fluid and filter every
50,000 miles
(83
000 km) if the vehicle is mainly driven under one or
more
of these conditions:
In heavy city traffic where the outside temperature
regularly reaches 90°F (32°C) or higher.
In hilly or mountainous terrain.
When doing frequent trailer towing.
Uses such as found in taxi, police or delivery
If you do not use your vehicle under any of these
conditions, change the fluid and filter every
100,000 miles (1 66 000 km).
See
Part A: Scheduled Maintenance Services on
page
6-4.
service.
How to Check
Because this operation can be a little difficult, you may
choose to have this done at the dealership service
department.
If you do it yourself, be sure to follow all the instructions
here, or you could get a false reading on the dipstick.
Notice: Too much or too little fluid can damage
your transmission. Too much can mean that some
of the fluid could come out and fall on hot engine
part
or exhaust system parts, starting a fire.
Too little fluid could cause the transmission to overheat. Be sure to get an accurate reading if you
check your transmission fluid.
Wait at least
30 minutes before checking the
transmission fluid level
if you have been driving:
0 When outside temperatures are above 90°F (32°C).
At high speed for quite a while.
In heavy traffic - especially in hot weather.
While pulling a trailer.
To get the right reading, the fluid should be at normal
operating temperature, which is 180°F
to 200°F
(82°C to 93°C).
5-2
1

Coolant Surge Tank Pressure Cap
The coolant surge tank
pressure cap must be fully
installed on the coolant
surge tank.
Nofice: Your pressure cap is a pressure-type cap
and must be tightly installed to prevent coolant loss
and possible engine damage from overheating. See “Capacities and Specifications” for more
information.
Engine Overheating
You will find a coolant temperature gage on your
vehicle’s instrument panel. See
Engine Coolant
Temperature Gage
on page 3-36. In addition, you will
find a LOW COOLANT, ENGINE OVERHEATED and a
REDUCED ENGINE POWER message in the DIC on
the instrument panel. See
Driver lnformation Center
(DIC)
on page 3-43.
Overheated Engine Protection
Operating Mode
If an overheated engine condition exists and the
REDUCED ENGINE POWER message is displayed, an
overheat protection mode which alternates firing groups
of cylinders helps prevent engine damage. In this mode,
you will notice a
loss in power and engine performance.
This operating mode allows your vehicle to be driven to
a
safe place in an emergency. Driving extended miles (km)
and/or towing a trailer in the overheat protection mode
should be avoided.
Nofice: After driving in the overheated engine
protection operating mode, to avoid engine damage,
allow the engine to cool before attempting any repair.
The engine oil will be severely degraded. Repair the
cause of coolant
loss, change the oil and reset the oil
life system. See “Engine
Oil” in the Index.
5-27

If No Steam Is Coming From
Your Engine
An overheat warning, along with a low coolant message,
can indicate
a serious problem. See “Low Coolant”
under
DIC Warnings and Messages on page 3-53.
If you get an engine overheat warning with no low
coolant message, but see or hear no steam, the problem
may not be too serious. Sometimes the engine can
get a little
too hot when you:
Climb a long hill on a hot day.
Stop after high-speed driving.
Idle for long periods in traffic.
Tow a trailer. See “Driving on Grades” under
Towing a Trailer on page 4-51.
If you get the overheat warning with no sign of steam,
try this for a minute or
so:
1. If your air conditioner is on, turn it off.
2. Turn on your heater to full hot at the highest fan
speed and open the window as necessary.
3. If you’re in a traffic jam, shift to NEUTRAL (N);
otherwise, shift to the highest gear while
driving
- AUTOMATIC OVERDRIVE (@ ).
If you no longer have the overheat warning, you can
drive. Just
to be safe, drive slower for about 10 minutes.
If the warning doesn’t come back on, you can drive
normally.
If the warning continues, pull over, stop, and park your
vehicle right away.
If there’s still no sign of steam, push down the accelerator
until the engine speed
is about twice as fast as normal
idle speed for at least three minutes while you’re parked.
If you still have the warning, turn off the engine andget
everyone out
of the vehicle until it cools down. Also, see
Overheated Engine Protection Operating Mode listed
previously in this section.
You may decide not
to lift the hood but to get service
help right away.
5-29

6. Then replace the
pressure cap. Be sure
the pressure cap is
hand-tight and
fully seated. Engine Fan Noise
Your vehicle has a clutched engine cooling fan. When the
clutch is engaged, the fan spins faster to provide more air
to cool the engine. In most everyday driving conditions,
the fan is spinning slower and the clutch is not fully
engaged. This improves fuel economy and reduces fan
noise. Under heavy vehicle loading, trailer towing and/or
high outside temperatures, the fan speed increases as
the clutch more fully engages.
So you may hear an
increase in fan noise. This is normal and should not be
mistaken as the transmission slipping or making extra
shifts. It
is merely the cooling system functioning properly.
The fan will slow down when additional cooling is not
required and the clutch disengages.
You may also hear this fan noise when you start the
engine. It will go away as the fan clutch partially
disengages.
5-36

DRIVER UNLOCK
Fuses Usage
LT TRLR ST/TRN Left Turn SignaVStop Trailer
LT TRN Left Turn Signals
and
Sidemarkers
VEH STOP
5-97