ECU GMC SIERRA 2004 Workshop Manual

When you are back on roads, though, be sure to
replace the air dam.
Notice:Operating your vehicle for extended
periods without the front bumper lower air dam
installed can cause improper air ¯ow to the engine
and may allow things like fog lamps or tow hooks
on the front of your vehicle to be damaged. Always
be sure to replace the front bumper air dam when
you are ®nished off-road driving.
To reinstall the lower air dam, do the following:
1. Line up each push-pin
with its intended
retainer and push the
washer portion of
the push-pin toward
the retainer until it locks
into place.2. Push the ¯at end of the
push-pin toward the
retainer until it
locks into place,
making sure each is
secure.
Before You Go Off-Roading
There are some things to do before you go out. For
example, be sure to have all necessary maintenance
and service work done. Check to make sure all
underbody shields (if so equipped) are properly
attached. Be sure you read all the information about
your four-wheel-drive vehicle in this manual. Is
there enough fuel? Is the spare tire fully in¯ated? Are
the ¯uid levels up where they should be? What are the
local laws that apply to off-roading where you will be
driving? If you do not know, you should check with law
enforcement people in the area. Will you be on
someone's private land? If so, be sure to get the
necessary permission.
4-22

Loading Your Vehicle for Off-Road
Driving
There are some important things to remember about
how to load your vehicle.
·The heaviest things should be on the load ¯oor and
forward of your rear axle. Put heavier items as far
forward as you can.
·Be sure the load is secured properly, so driving on
the off-road terrain does not toss things around.
{CAUTION:
·Cargo on the load ¯oor piled higher than
the seatbacks can be thrown forward
during a sudden stop. You or your
passengers could be injured. Keep cargo
below the top of the seatbacks.
·Unsecured cargo on the load ¯oor can be
tossed about when driving over rough
terrain. You or your passengers can be
struck by ¯ying objects. Secure the cargo
properly.
·Heavy loads on the roof raise the vehicle's
center of gravity, making it more likely to
roll over. You can be seriously or fatally
injured if the vehicle rolls over. Put heavy
loads inside the cargo area, not on the
roof. Keep cargo in the cargo area as far
forward and low as possible.
You will ®nd other important information in this manual.
See
Loading Your Vehicle on page 4-57andTires
on page 5-76.
4-23

·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.
Winter Driving
Here are some tips for winter driving:
·Have your vehicle in good shape for winter.
·You may want to put winter emergency supplies in
your vehicle.
Include an ice scraper, a small brush or broom, a
supply of windshield washer ¯uid, a rag, some winter
outer clothing, a small shovel, a ¯ashlight, a red
cloth and re¯ective warning triangles. And, if you will be
driving under severe conditions, include a small bag
of sand, a piece of old carpet or a couple of burlap bags
to help provide traction. Be sure you properly secure
these items in your vehicle.
Driving on Snow or Ice
Most of the time, those places where your tires meet
the road probably have good traction.
However, if there is snow or ice between your tires and
the road, you can have a very slippery situation. You
will have a lot less traction or ªgripº and will need to be
very careful.
4-47

Four-Wheel-Drive Vehicles Equipped with
Transfer Case (NP1, NP2 and NP8)
Use the following procedure to tow your vehicle:
1. Shift an automatic transmission to PARK (P), or a
manual transmission to FIRST (1).
2. Turn the engine off, but leave the ignition on.
3. Firmly set the parking brake.
4. Securely attach the vehicle being towed to the tow
vehicle.
{CAUTION:
Shifting a four-wheel-drive vehicle's transfer
case into NEUTRAL can cause your vehicle to
roll even if the transmission is in Park (P) for
an automatic transmission, or if your vehicle is
in gear, for a manual transmission. You or
others could be injured. Make sure the parking
brake is ®rmly set before you shift the transfer
case to NEUTRAL.5. Shift the transfer case to NEUTRAL. See
Four-Wheel Drive on page 2-35for the proper
procedure to select the neutral position for
your vehicle.
6. Release the parking brake only after the vehicle
being towed is ®rmly attached to the towing
vehicle.
7. Turn the ignition off and leave the steering column
unlocked.
4-55

Dolly Towing
Two-Wheel-Drive Vehicles
Two-wheel-drive vehicles should not be towed with the
rear wheels on the ground. Two-wheel-drive
transmissions have no provisions for internal lubrication
while being towed.
Two-wheel-drive vehicles can be dolly towed with the
front wheels on the ground provided that the wheels are
straight and the steering column has been locked.
Four-Wheel-Drive Vehicles
Use the following procedure to tow your vehicle:
1. Drive the vehicle up onto the tow dolly.
2. Shift an automatic transmission to PARK (P), or a
manual transmission to FIRST (1).
3. Turn the engine off, but leave the ignition on.
4. Firmly set the parking brake.
5. Securely attach the vehicle being towed to the tow
dolly.
{CAUTION:
Shifting a four-wheel-drive vehicle's transfer
case into NEUTRAL can cause your vehicle to
roll even if the transmission is in Park (P) for
an automatic transmission, or if your vehicle is
in gear, for a manual transmission. You or
others could be injured. Make sure the parking
brake is ®rmly set before you shift the transfer
case to NEUTRAL.
4-56

Certi®cation/Tire Label
The Certi®cation/Tire label is found on the rear edge of
the driver's door.
The label shows the size of your original tires and the
in¯ation pressures needed to obtain the gross weight
capacity of your vehicle. This is called the GVWR (Gross
Vehicle Weight Rating). The GVWR includes the
weight of the vehicle, all occupants, fuel and cargo.The Certi®cation/Tire label also tells you the maximum
weights for the front and rear axles, called Gross
Axle Weight Rating (GAWR). To ®nd out the actual loads
on your front and rear axles, you need to go to a
weigh station and weigh your vehicle. Your dealer can
help you with this. Be sure to spread out your load
equally on both sides of the centerline.
Never exceed the GVWR for your vehicle, or the GAWR
for either the front or rear axle.
The Certi®cation/Tire label also contains important
information about your Front Axle Reserve Capacity.
See ªFront Axle Reserve Capacityº later in this section.
And, if you do have a heavy load, you should spread
it out.{CAUTION:
In the case of a sudden stop or collision,
things carried in the bed of your truck could
shift forward and come into the passenger
area, injuring you and others. If you put things
in the bed of your truck, you should make sure
they are properly secured.
4-61

{CAUTION:
Do not load your vehicle any heavier than the
GVWR, or either the maximum front or rear
GAWR. If you do, parts on your vehicle can
break, and it can change the way your vehicle
handles. These could cause you to lose
control and crash. Also, overloading can
shorten the life of your vehicle.
Notice:Overloading your vehicle may cause
damage. Repairs would not be covered by your
warranty. Do not overload your vehicle.
This will help you decide how much cargo and installed
equipment your truck can carry.
Using heavier suspension components to get added
durability might not change your weight ratings. Ask your
dealer to help you load your vehicle the right way.
If you put things inside your vehicle ± like suitcases,
tools, packages, or anything else ± they go as fast
as the vehicle goes. If you have to stop or turn quickly,
or if there is a crash, they'll keep going.
{CAUTION:
Things you put inside your vehicle can strike
and injure people in a sudden stop or turn, or
in a crash.
·Put things in the cargo area of your
vehicle. Try to spread the weight evenly.
·Never stack heavier things, like suitcases,
inside the vehicle so that some of them
are above the tops of the seats.
·Do not leave an unsecured child restraint
in your vehicle.
·When you carry something inside the
vehicle, secure it whenever you can.
·Do not leave a seat folded down unless
you need to.
There's also important loading information for off-road
driving in this manual. See ªLoading Your Vehicle
for Off-Road Drivingª under
Off-Road Driving with Your
Four-Wheel-Drive Vehicle on page 4-20.
4-62

Payload
Payload capacity is the maximum load capacity that your
vehicle can carry. Be sure to include the weight of the
occupants as part of your load. If you added any
accessories or equipment after your vehicle left the
factory, remember to subtract the weight of these things
from the payload. Your dealer can help you with this.
Remember not to exceed the Gross Axle Weight Rating
(GAWR) of the front or rear axle.
Two-Tiered Loading
By positioning four 2º x 6º wooden planks across the
width of the pickup box, you can create an upper load
platform. The planks must be inserted in the pickup box
depressions. The length of the planks must allow for at
least a 3/4 inch (2 cm) bearing surface on each end of
the plank.
When using this upper load platform, be sure the load is
securely tied down to prevent it from shifting. The load's
center of gravity should be positioned in a zone over the
rear axle. The zone is located in the area between the
front of each wheel well and the rear of each wheel well.
The center of gravity height must not extend above the
top of the pickup box ¯areboard.
Any load that extends beyond the vehicle's taillamp area
must be properly marked according to local laws and
regulations.Remember not to exceed the Gross Axle Weight Rating
(GAWR) of the front or rear axle.
Add-On Equipment
When you carry removable items, you may need to put a
limit on how many people you carry inside your vehicle.
Be sure to weigh your vehicle before you buy and install
the new equipment.
Notice:Overloading your vehicle may cause
damage. Repairs would not be covered by your
warranty. Do not overload your vehicle.
Remember not to exceed the Gross Axle Weight Rating
(GAWR) of the front or rear axle.
*Equipment Maximum Weight
Ladder Rack and Cargo 750 lbs. (340 kg)
Cross Toolbox and Cargo 400 lbs. (181 kg)
Side Boxes and Cargo 250 lbs. per side (113 kg
per side)
*The combined weight for all rail-mounted equipment
should not exceed 1,000 lbs. (454 kg) excludes
1500 crew cab models with 5' 8²box length. A
reinforcement kit for rail-mounted add-on equipment is
recommended. See your dealer. Ladder racks are not
recommended for 1500 crew cab models (with 5' 8²
pick-up box length.) Maximum recommended cross
mounted toolbox and cargo weight is 300 lbs. (136 kg)
for the 1500 crew cab (with 5' 8²pick-up box length.)
4-63

Here are some guidelines for safely carrying a snow
plow on your vehicle:
·Make sure the weight on the front and rear axles
does not exceed the axle rating for each.
·For the front axle, if more cargo or passengers
must be carried, appropriate counter ballast must be
installed rear of the rear axle. Counter ballast
must be properly secured so it will not move during
driving.
·Follow the snow plow manufacturer's
recommendations regarding rear ballast. Rear
ballast may be required to ensure a proper front and
rear weight distribution ratio, even though the
actual weight at the front axle may be less than the
front axle rating.
·The snow plow manufacturer or installer can assist
you in determining the amount of rear ballast
required, to help make sure your snowplow/vehicle
combination does not exceed the GVW rating,
the front and rear axle ratings, and the front and
rear weight distribution ratio.
·The total vehicle must not exceed the GVW rating.
Q:What is front axle reserve capacity, and how do
I calculate it?
A:Front axle reserve capacity is the difference
between your front GAWR and the front axle
weight of your truck with full fuel and passengers.
Basically, it is the amount of weight you can
add to your front axle before reaching your
front GAWR.
The front axle reserve capacity for your vehicle can be
found in the lower right corner of the Certi®cation/Tire
label, as shown.
United States
Canada
4-65

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 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.
4-92