Tow GMC ENVOY 2008 Service Manual

Maximum trailer weight is calculated assuming only the
driver is in the tow vehicle and it has all the required
trailering equipment. The weight of additional optional
equipment, passengers and cargo in the tow vehicle
must be subtracted from the maximum trailer weight.Look in the following chart to nd the maximum trailer
weight for your vehicle.
Vehicle Axle Ratio Max.Trailer Wt. *GCWR
2WD Envoy (4.2 L L6 Engine)3.42 5,300 lbs (2 404 kg) 10,000 lbs (4 536 kg)
3.73 5,800 lbs (2 631 kg) 10,500 lbs (4 763 kg)
4.10 6,300 lbs (2 858 kg) 11,000 lbs (4 990 kg)
2WD Envoy (5.3 L V8 Engine)3.42 6,100 lbs (2 767 kg) 11,000 lbs (4 990 kg)
3.73 6,600 lbs (2 994 kg) 11,500 lbs (5 216 kg)
4WD Envoy (4.2 L L6 Engine)3.42 5,200 lbs (2 359 kg) 10,000 lbs (4 536 kg)
3.73 5,700 lbs (2 858 kg) 10,500 lbs (4 763 kg)
4.10 6,200 lbs (2 812 kg) 11,000 lbs (4 990 kg)
4WD Envoy (5.3 L V8 Engine)3.42 6,000 lbs (2 721 kg) 11,000 lbs (4 990 kg)
3.73 6,500 lbs (2 948 kg) 11,500 lbs (5 216 kg)
*The Gross Combination Weight Rating (GCWR) is the total allowable weight of the completely loaded vehicle and
trailer including any passengers, cargo, equipment and conversion. The GCWR for your vehicle should not be
exceeded.
Ask your dealer for our trailering information or advice,
or write us at our Customer Assistance Offices. See
Customer Assistance Offices on page 7-6for more
information.
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Weight of the Trailer Tongue
The tongue load (A) of any trailer is an important weight
to measure because it affects the total or gross weight of
your vehicle. The Gross Vehicle Weight (GVW) includes
the curb weight of the vehicle, any cargo you may carry in
it, and the people who will be riding in the vehicle. If you
have a lot of options, equipment, passengers or cargo in
your vehicle, it will reduce the tongue weight your vehicle
can carry, which will also reduce the trailer weight your
vehicle can tow. And if you will tow a trailer, you must add
the tongue load to the GVW because your vehicle will be
carrying that weight, too. See Loading Your Vehicle for
more information about your vehicle’s maximum load
capacity.
The trailer tongue weight (A) should be 10 percent to
15 percent of the total loaded trailer weight (B), up to a
maximum of 400 lbs (181 kg) with a weight carrying hitch.The trailer tongue weight (A) should be 10 percent to
15 percent of the total loaded trailer weight (A), up to a
maximum of 900 lbs (408 kg) for a weight distributing
hitch.
Do not exceed the maximum allowable tongue weight
for your vehicle. Choose the shortest hitch extension
that will position the hitch ball closest to the vehicle.
This will help reduce the effect of trailer tongue weight
on the rear axle.
After you’ve loaded your trailer, weigh the trailer and
then the tongue, separately, to see if the weights
are proper. If they aren’t, you may be able to get
them right simply by moving some items around
in the trailer.
Trailering may be limited by the vehicle’s ability to carry
tongue weight. Tongue weight cannot cause the vehicle
to exceed the GVWR (Gross Vehicle Weight Rating) or
the RGAWR (Rear Gross Axle Weight Rating). The effect
of additional weight may reduce your trailering capacity
more than the total of the additional weight.
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Weight Distributing Hitches and Weight
Carrying Hitches
When using a weight-distributing hitch, the hitch must
be adjusted so the distance (A) remains the same both
before and after coupling the trailer to the tow vehicle.
If you use a step-bumper hitch, the bumper could
be damaged in sharp turns. Make sure there is ample
room when turning to avoid contact between the
trailer and the bumper.
If you will be pulling a trailer that, when loaded, will
weigh more than 5,000 lbs (2 270 kg) be sure to use a
properly mounted weight-distributing hitch and swaycontrol of the proper size. This equipment is very
important for proper vehicle loading and good handling
when driving. Always use a sway control if the trailer will
weigh more than these limits. You can ask a hitch dealer
about sway controls.
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. Follow
the manufacturer’s recommendation for attaching safety
chains and do not attach them to the bumper. 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 1,500 lbs. (680 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.
Since your vehicle is equipped with StabiliTrak
®, your
trailer brakes cannot tap into the vehicle’s hydraulic
brake system. (A) Body to Ground Distance, (B) Front of Vehicle
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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 can not
see or smell CO. It can cause unconsciousness
or death. SeeEngine Exhaust on page 2-37.
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.
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.
SeeDual Climate Control System on
page 3-21.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 all trailer hitch parts and
attachments, safety chains, electrical connection, 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.
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.
4-52

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.
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 THIRD (3) or a lower gear, under heavy
loads or hilly conditions.
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, seeEngine Overheating
on page 5-28.
4-53

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, and
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 uid (don’t overll),
engine oil, axle lubricant, belt(s), 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.
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Trailer Wiring Harness
Your vehicle may be equipped with the seven-wire
trailer towing harness. This harness has a seven-pin
universal heavy-duty trailer connector (if equipped with
the trailering package) that is attached to a bracket
on the hitch platform. If your vehicle is not equipped with
the heavy-duty trailer connector, you may purchase
one from your dealer.The seven-wire harness contains the following trailer
circuits:
Yellow: Left Stop/Turn Signal
Dark Green: Right Stop/Turn Signal
Brown: Running Lamps
White: Ground
Light Green: Back-up Lamps
Red: Battery Feed
Dark Blue: Electric Brakes
If you need to tow a light-duty trailer with a standard
four-way round pin connector, an adapter connector is
available from your dealer.
If you are charging a remote (non-vehicle) battery, turn
on the headlamps to boost the vehicle system voltage
and properly charge the battery.
Your vehicle may also be equipped with wiring for an
electric trailer brake controller. These wires are located
inside the vehicle on the driver’s side under the
instrument panel. These wires should be connected to
an electric trailer brake controller by your dealer or
a qualied service center.
4-56

Engine Oil
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. See
Engine Compartment Overview on page 5-12for
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.
When to Add Engine Oil
L6 Engine
V8 Engine
5-16

Checking the Fluid Level
Prepare your vehicle as follows:
1. Park your vehicle on a level place. Keep the engine
running.
2. With the parking brake applied, place the shift lever
in PARK (P).
3. With your foot on the brake pedal, move the shift
lever through each gear range, pausing for about
three seconds in each range. Then, position the
shift lever in PARK (P).
4. Let the engine run at idle for three minutes or more.Then, without shutting off the engine, follow these steps:
1. Flip the handle up and then remove the dipstick
and wipe it with a clean rag or paper towel.
The automatic
transmission dipstick
handle with this symbol on
it is located in the engine
compartment on the
passenger’s side of the
vehicle.
SeeEngine Compartment Overview on page 5-12
for more information on location.
2. Reinstall it back in all the way, wait three seconds
and then pull it back out again. If the dipstick does
not go down the tube easily, turn the blade and
try again until it is fully inserted in the tube.
5-24

If Steam Is Coming From Your Engine
{CAUTION:
Steam from an overheated engine can burn
you badly, even if you just open the hood. Stay
away from the engine if you see or hear steam
coming from it. Just turn it off and get
everyone away from the vehicle until it cools
down. Wait until there is no sign of steam or
coolant before you open the hood.
If you keep driving when your engine is
overheated, the liquids in it can catch re. You
or others could be badly burned. Stop your
engine if it overheats, and get out of the vehicle
until the engine is cool.
Notice:If your engine catches re because you
keep driving with no coolant, your vehicle can
be badly damaged. The costly repairs would not be
covered by your warranty.
If No Steam Is Coming From Your
Engine
If you get an engine overheat warning 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.
If you get the overheat warning with no sign of steam,
try this for a minute or so:
1. In heavy traffic, let the engine idle in NEUTRAL (N)
while stopped. If it is safe to do so, pull off the road,
shift to PARK (P) or NEUTRAL (N) and let the
engine idle.
2. Turn on your heater to full hot at the highest fan
speed and open the windows as necessary.
5-29