2003 GMC SIERRA DENALI engine

If you drive regularly in steep country, or if you’re
planning to visit there, here are some tips that can make
your trips safer and more enjoyable. See
Operating
Your All-Wheel-Drive Vehicle
Off Paved Roads on
page
4-16 for information about driving off-road.
Keep your vehicle in good shape. Check all fluid
levels and also the brakes, tires, cooling system
and transmission. These parts can work hard
on mountain roads.
Know how to go down hills. The most important
thing to know is this: let your engine do some of
the slowing down. Shift to a lower gear when you go
down a steep or long hill.
If you don’t I R down, your -____ 3s COL- ge-
so hot that they wouldn’t work well. You would
then have poor braking or even none going
down a hill. You could crash. Shift down to let
your engine assist your brakes on a steep downhill slope. Coasting
UVwnlll..
..I NEUTRAL (N) G. .... h the
ignition
off is dangerous. Your brakes will have
to do all the work
of slowing down. They could
get
so hot that they wouldn’t work well. You
would then have poor braking or even none
going down a
hill. You could crash. Always
have your engine running and your vehicle in
gear when you go downhill.
Know how to go uphill. You may want to shift down to
a lower gear. The lower gears help cool your engine
and transmission, and you can climb the hill better.
roads in hills or mountains. Don’t swing wide or cut
across the center of the road. Drive at speeds that let
you stay in your own lane.
As you go over the top of a hill, be alert. There could
be something in your lane, like a stalled car or an
accident.
You may see highway signs on mountains that warn
of special problems. Examples are long grades,
passing or no-passing zones, a falling rocks area or
winding roads. Be alert to these and take appropriate
action.
Stay in your own lane when driving on two-lane
4-37

If You’re Caught in a Blizzard
If you are stopped by heavy snow, you could be in a
serious situation. You should probably stay with
your vehicle unless you know for sure that you are near
help and you can hike through the snow. Here are
some things to do to summon help and keep yourself
and your passengers safe:
4-40
Turn on your hazard flashers.
Tie a red cloth to your vehicle to alert police that
you’ve been stopped by the snow.
Put on extra clothing or wrap a blanket around you.
If you have no blankets or extra clothing, make
body insulators from newspapers, burlap bags, rags,
floor mats
- anything you can wrap around
yourself or tuck under your clothing to keep warm.
. _-. I:. .
You can run the engine to keep warm, but be careful.

Snow can trap exhaust gases under your
vehicle. This can cause deadly CO (carbon
monoxide) gas to get inside. CO could
overcome you and kill you. You can’t see
it or
smell
it, so you might not know it is in your
vehicle. Clear away snow from around the
base of your vehicle, especially any that is
blocking your exhaust pipe. And check around
again from time to time to be sure snow
doesn’t collect there.
Open a window just a little on the side of the
vehicle that’s away from the wind. This will
help keep
CO out. Run your
engine only as long as you must. This saves
fuel. When you run the engine, make it go a little
faster than just idle. That is, push the accelerator
slightly. This uses less fuel for the heat that you get and
it keeps the battery charged.
You will need a
well-charged battery to restart the vehicle, and possibly
for signaling later on with your headlamps. Let the
heater run for a while.
Then, shut the engine
off and close the window almost
all the way to preserve the heat. Start the engine
again and repeat this only when you feel really
uncomfortable from the cold.
But do it as little as
possible. Preserve the fuel as long as you can. To help
keep warm, you can get out of the vehicle and do
some fairly vigorous exercises every half hour or
so until
help comes.
4-41

If You Are Stuck: In Sand, Mud, Ice
or Snow
in order to free your vehicle when it is stuck, you will
need to spin the wheels, but you don’t want to spin your
wheels too fast. The method known as “rocking” can
help you aet out when you’re stuck, but you must
use cauti
.
If you let your tires spin at high speed, they
can explode, and you or others could be
injured.
And, the transmission or other parts of
the vehicle can overheat. That could cause an
CAUTION: (Continued) engine compartment fire or other
damage.
When you’re stuck, spin the wheels as little as
possible. Don’t spin the wheels above
25 mph
(55 km/h) as shown on the speedometer.
Nofice: Spinning your wheels can destroy parts of
your vehicle as well as the tires. If you spin the
wheels too fast while shifting your transmission back and forth, you can destroy your transmission.
For information about using tire chains on your
vehicle, see
Tire Chains on page 5-68.
4-42

Towing a Trailer
If you don’t ,se the correct eq-., ...__. t 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. Additional rear axle maintenance is required for a vehicle used to tow a trailer. See
“Scheduled Maintenance Services” in the Index.
To identify the vehicle trailering capacity of your vehicle,
you should read the information in “Weight of the
Trailer” that appears later in this section.
If yours was built with trailering options, as many are,
it’s ready for heavier trailers. But trailering is different
than just driving your vehicle by itself. Trailering means
changes in 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.
If You Do Decide To Pull A Trailer
If you do, here are some important points:
e
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
if your trailer will
weigh
5,000 Ibs. (2 270 kg) or less. You should
always use a sway control
if your trailer will weigh
more than
5,000 Ibs. (2 270 kg). You can ask a
hitch dealer about sway controls.
Don’t tow a trailer at all during the first
500 miles
(800 km) your new vehicle is driven. Your engine,
axle or other parts could be damaged.
4-5 1

Then, during the first 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.
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 (e.g., under heavy loads and/or hilly
conditions).
Three important considerations have to do with weight:
the weight of the trailer,
the weight of the trailer tongue
and the weight on your vehicle’s tires.
Tow/HauI Mode
Tow/haul is a feature that assists when pulling a heavy
trailer or a large or heavy load. The purpose
of the
tow/haul mode is to:
Reduce the frequency and improve the predictability
of transmission shifts when pulling a heavy trailer or
a large or heavy load.
Provide the same solid shift feel when pulling a
heavy trailer or a large or heavy load as when
the vehicle is unloaded.
Improve control of vehicle speed while requiring
less throttle pedal activity when pulling a heavy
trailer or a large or heavy load.
Your vehicle may be equipped with a switch at the end
of the shift lever which when pressed enables
tow/haul. When the switch is pressed, a light on the
instrument panel will illuminate to indicate that tow/haul
has been selected. Tow/haul may be turned
off by
pressing the switch again, at which time the indicator
light on the instrument panel will turn
off. The vehicle will
automatically turn
off tow/haul every time it is started.
4-52

Tow/haul is designed to be most effective when the
vehicle and trailer combined weight is at least
75 percent
of the vehicle’s Gross Combined Weight Rating
(GCWR). See Weight of the Trailer later in this section.
Tow/haul
is most useful under the following driving
conditions:
When pulling a heavy trailer or a large or heavy
When pulling a heavy trailer or a large or heavy
load
through rolling terrain.
load in stop and go traffic.
When pulling a heavy trailer or a large or heavy
load in busy parking lots where improved low
speed control of the vehicle is desired.
Operating the vehicle in tow/haul when lightly loaded or
with no trailer at all will not cause damage. However,
there is no benefit to the selection of tow/haul when the
vehicle is unloaded. Such a selection when unloaded
may result in unpleasant engine and transmission driving
characteristics and reduced fuel economy. Tow/haul
is recommended only when pulling a heavy trailer or a
large or heavy load.
Weight of the Trailer
How heavy can a trailer safely be?
It depends
on how you plan to use your rig. For
example, speed, altitude, road grades, outside
temperature and how much your vehicle is used to pull
a trailer are all important. And, it can also depend
on any special equipment that you have on your vehicle.
Use one of the following charts to determine how
much your vehicle can weigh, based upon your vehicle
model and options.
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.
4-53

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