1998 GMC ENVOY Owners Manual

Scanning the Terrain
Off-road driving can take you over many different kinds
of terrain.
You need to be familiar with the telrain and its
many different features. Here are some things to consider.
S~lr$uce Conditions. Off-roading can take you over
hard-packed dirt, gravel, rocks, grass, sand, mud, snow
or ice. Each of these surfaces affects the steering,
acceleration and braking of your vehicle
in different
ways. Depending upon the kind of surface
you are on,
you may experience slipping, sliding, wheel spinning,
delayed acceleration, poor traction and longer
braking distances.
Su$ace Obstucles . Unseen or hidden obstacles can be
hazardous.
A rock, log, hole, rut or bump can startle you if
you're not prepared for them. Often these obstacles are
hidden by grass, bushes, snow
or even the rise and fall of
the terrain itself. Here are
some things to consider:
0 Is the path ahead clear'?
Will the surface texture change abruptly up ahead?
Does the travel take you uphill or downhill? (There's
more discussion of these subjects later.)
Will you have to stop suddenly or change
direction quickly'? When you
drive over obstacles or rough terrain, keep
a
firm grip on the steering wheel. Ruts, troughs or other
surhce features can jerk the wheel out
of your hands if
you're not prepared.
When you drive over bumps, rocks, or other obstacles,
your wheels can leave the ground.
If this happens, even
with one or two wheels, you can't control the vehicle as
well or at all.
Because you
will be on an unpaved surface, it's
especially important to avoid sudden acceleration,
sudden turns or sudden braking.
In a way, off-road driving requires a different kind of
alertness from driving on paved roads and highways.
There are no road signs, posted speed limits or signal
lights.
You have to use your own good judgment about
what is safe and what isn't.
Drinking and driving can be very dangerous
on any
road. And this is certainly true for off-road driving. At
the very time
you need special alertness and driving
skills, your reflexes, perceptions and judgment can be
affected by even
a small amount of alcohol. You could
have a serious
-- or even fatal -- accident if you drink
and drive or ride with a driver who has been drinking.
See "Drunken Driving"
in the Index.
4-18
ProCarManuals.com

Driving on Off-Road Hills
Off-road driving often takes you up, down or across a
hill. Driving safely on hills requires good judgment and
an understanding of what your vehicle can and can't do.
There are some hills
that simply can't be driven, no
matt how
well built the vehicle.
can easily see all the way to the top. On a large hill, the
incline may get steeper as you near the top.
but you may
not see this because the crest of the hill is hidden by
bushes.
grass or shrubs.
Here are some other things to consider
as you approach
a hill.
-0
Many hills are simply too steep for any vehicle. If
you drive up them, you will stall. If you drive
down them, you can't control your speed.
If you
drive across them,
you will roll over. You could be
seriously injured or killed.
If you have any doubt
about the steepness, don't drive the hill.
Approaching a Hill
When you approach a hill, you need to decide if it's one
of those hills that's just too steep to climb, descend or
cross. Steepness can be hard to judge. On a very small
hill, for example, there may be a smooth. constant
incline with only
a small change in elevation where you
0
0
0
0
0
Is there a constant incline, or does the hill get sharply
steeper
in places?
Is there good traction on the hillside, or will the
surface cause tire slipping'!
Is there a straight path up or down the hill so you
won't have to make turning Inaneuvers'!
Are there obstructions
on the hill that can block your
path (boulders, trees. logs or ruts)'?
What's beyond the
hill? Is there a cliff, an
embankment. a drop-off.
a fence? Get out and walk
the
hill if you don't know. It's the smart way to
find out.
Is the hill simply too rough? Steep hills of'ten have
ruts, gullies, troughs and exposed rocks because they
are more susceptible to the effects of erosion.
4-19
I
ProCarManuals.com

Driving Uphill
Once you decide you can safely drive up the hill, you
need to take some special steps.
Use a low gear and get a firm grip on the
steering wheel.
Get a smooth start up the hill and try to maintain
your speed. Don’t use more power than you need,
because you don’t want your wheels to start spinning
or sliding.
0 Try to drive straight up the hill if at all possible. If
the path twists and turns, you might want to find
another route.
Ease up on your speed as you approach the top of
0 Attach a flag to the vehicle to make you more visible
0 Sound the horn as you approach the top of the hill to
0 Use your headlamps even during the day. They make
the
hill.
to approaching traffic on trails or hills.
let opposing traffic know you’re there.
you more visible to oncoming traffic.
Turning or driving across steep hills can be
dangerous. You could lose traction, slide
sideways, and possibly roll over. You could be
seriously injured or killed. When driving up hills,
always try to go straight up.
A CAUTION:
Driving to the top (crest) of a hill at full speed can
cause an accident. There could be
a drop-off,
embankment, cliff, or even another vehicle. You
could be seriously injured or killed.
As you near
the top
of a hill, slow down and stay alert.
4-20
ProCarManuals.com

What should I do if my vehicle stalls, or is about
to stall, and
I can’t make it up the hill?
A: If this happens, there are some things you should
0
0
0
0
do, and there are some things you must not do.
First, here’s what you
should do:
Push the brake pedal to stop the vehicle and keep
it
from rolling backwards. Also, apply the
parking brake.
If your engine is still running, shift the transmission
to REVERSE
(R), release the parking brake, and
slowly back down the
hill in REVERSE (R).
If your engine has stopped running, you’ll need to restart
it. With the brake pedal depressed and the parking brake
still applied, shift the transmission
to PARK (P) and
restart the engine. Then, shift to REVERSE
(R), release
the parking brake, and slowly back down the
hill as
straight as possible
in REVERSE (R).
As you are backing down the hill, put your left hand
on the steering wheel at
the 12 o’clock position. This
way. you’ll be able to tell
if your wheels are straight
and maneuver
as you back down. It’s best that you
back down the
hill with your wheels straight rather
than
in the left or right direction. Turning the wheel
too far to the left or right will increase the possibility
of
a rollover. Here
are some things you
must r7ot do if you stall, or are
about to stall, when going up
a hill.
0 Never attempt to prevent a stall by shifting into
NEUTRAL
(N) to “rev-up” the engine and regain
forward momentum. This won’t work. Your vehicle
will roll backwards very quickly and you could go
out of control.
Instead, apply the regular brake to stop
the vehicle.
Then apply the parking brake. Shift to REVERSE
(R), release the parking brake, and slowly back
straight down.
0 Never attempt to turn around if you are about to stall
when going up
a hill. If the hill is steep enough to
stall your vehicle, it’s steep enough to cause you to
roll over if you turn around. If you can’t make it up
the
hill, you must back straight down the hill.
Q: Suppose, after stalling, I try to back down the
hill and decide
I just can’t do it. What should
I do?
A: Set the parking brake, put your transmission in
PARK (P) and turn off the engine. Leave the
vehicle and go get some help. Exit on the uphill
side and stay clear of the path the vehicle would
take
if it rolled downhill.
4-21
I
ProCarManuals.com

Driving Downhill
When off-roading takes you uownhill, you'll want to
consider
a number of things:
0
0
0
0
How steep is the downhill'? Will I be able to maintain
vehicle control?
What's the surface like'? Smooth'? Rough'? Slippery'?
Hard-packed dirt'? Gravel?
Are there hidden surface
obstacles'! Ruts?
Logs? Boulders'?
What's at the
bottom of the hill'! Is there a hidden
creek bank
or even a river bottom with large rocks?
If you decide you can go down a hill safely. then try to
keep your vehicle headed straight down. and use
a low
they won't have to do
all the work. Descend slowly,
keeping your vehicle under control at
all times.
b "ear. This way, engine drag can help your brakes and
0
0
A CAUTION:
Heavy braking when going down a hill can cause
your brakes
to overheat and fade. This could
cause
loss of control and a serious accident.
Apply the brakes lightly when descending a hill
and use a low gear to keep vehicle speed
under control.
Are there some things
I should not do when
driving down a hill?
A: Yes! These are important because if you ignore
them you could lose control and have
a
serious accident.
When driving downhill, avoid turns that take you
across the incline of the
hill. A hill that's not too
steep to drive down may be too steep to drive ~CI-OSS.
You could roll over
if you don't drive straight down.
Never
go downhill with the transmission in
NEUTRAL (N). This is crdled "free-wheeling." Your
brakes
will have to do all the work and could
overheat and fade.
4-22
ProCarManuals.com

Q.' Am I likely to stall when going downhill?
A: It's much nm-e likely to happen going uphill. But if
it happens going downhill, here's what to do.
0 Stop your vehicle by applying the regular brakes.
Shift to PARK (P) and. while still braking. restart
Apply the parking
brake.
the engine.
Shift back to a low gear, release the parking brake,
and drive straight d6wn.
0 If the engine won't start, get out and get
Driving Across an Incline
Sooner or later, an off-road trail will probab lelp. y go
across
the incline
of a hill. If this happens, you have to decide
whether to
try to dri\:e across the incline. Here are some
things to consider:
0 A hill that can be driven straight up or down may be
too steep to drive across. When you
go straight up or
down a
hill, the length of the wheel base (the
distance from the front wheels
to the rear wheels)
reduces the likelihood the vehicle
will tumble end
0
0
over end. But when you drive across an incline, the
much more narrow track width
(the distance between
the left and right wheels) may not prevent the vehicle
from tilting and rolling over.
Also. driving across an
incline puts more weight on the downhill wheels.
This could cause a downhill slide
or a rollover.
Surface conditions can be
a problem when you drive
across
a hill. Loose gravel, muddy spots, or even wet
If the vehicle slips sideways, it can hit something
that
will trip it (a rock, a rut, etc.) and roll over.
Hidden obstacles can make the steepness
of the
incline even worse.
If you drive across a rock with
the
uphill wheels. or if the downhill wheels drop into
a rut or depression, your vehicle can tilt even n1oI-e.
e orass can cause your tires to slip sideways. downhill.
For reasons like these.
you need to decide carefully
whether to
try to drive across an incline. Just because
the trail goes across the incline doesn't mean you have
to drive it. The last vehicle to try it might have
rolled over.
4-23
I
ProCarManuals.com

Driving across an incline that’s too steep will
make your vehicle roll over. You could be
seriously injured or killed.
If you have any doubt
about the steepness
of the incline, don’t drive
across it. Find another route instead.
What if I’m driving across an incline that’s not
too steep, but
I hit some loose gravel and start to
slide downhill. What should
I do?
A: If you feel your vehicle starting to slide sideways,
turn downhill. This should help straighten out the
vehicle and prevent the side slipping. However, a
much better way to prevent this is
to get out and
“walk the course”
so you know what the surface is
like before you drive it.
Stalling on an Incline
If your vehicle stalls when you’re crossing an incline, be
sure you (and your passengers) get out
on the uphill
side, even
if the door there is harder to open. If you get
out on the downhill side and the vehicle starts
to roll
over, you’ll be right in its path.
If you have to walk down the slope, stay out of the path
the vehicle will take
if it does roll over.
4-24
ProCarManuals.com

Getting out on the downhill (low) side of a vehicle
stopped across an incline is dangerous.
If the
vehicle rolls over, you could be crushed
or killed.
Always get out on the uphill (high) side of the
vehicle and stay well clear of the rollover path.
Driving in Mud, Sand, Snow or Ice
When you drive in mud, snow or sand, your wheels
won’t get good traction. You can’t accelerate
as quickly,
turning is more difficult, and you’ll need longer
braking distances.
It‘s best
to use a low gear when you’re in mud -- the
deeper
the mud, the lower the gear. In really deep mud,
the idea
is to keep your vehicle moving so you don’t
get stuck. When
you drive
on sand, you’ll sense a change in wheel
traction.
But it will depend upon how loosely packed the
sand is. On loosely packed sand (as on beaches or sand
dunes) your tires will tend
to sink into the sand. This has
an effect on steering, accelerating and braking. You may
want
to reduce the air pressure in your tires slightly
when driving on sand. This will improve traction.
Hard packed snow and ice offer the worst tire traction.
On these surfaces, it’s very easy
to lose control. On wet
ice, for example, the traction is
so poor that you will
have difficulty accelerating. And
if you do get moving,
poor steering and difficult braking can cause you to slide
out
of control.
LA CAU-ION:
Driving on frozen lakes, ponds or ~ ~ rers can be
dangerous. Underwater springs, currents under
the ice, or sudden thaws can weaken the ice. Your
vehicle could fall through the ice and you and
your passengers could drown. Drive your vehicle
on safe surfaces only.
4-25
1
ProCarManuals.com