2004 GMC SIERRA ECU

{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

Coolant Surge Tank Pressure Cap
SeeEngine Compartment
Overview on page 5-12for
more information on
location.
The coolant surge tank pressure cap must be fully
installed on the coolant surge tank.
Notice:If the pressure cap is not tightly installed,
coolant loss and possible engine damage may
occur. Be sure the cap is properly and tightly
secured.
Engine Overheating
You will ®nd a coolant temperature gage on your
vehicle's instrument panel. SeeEngine Coolant
Temperature Gage on page 3-46. In addition, you will
®nd a ENGINE OVERHEATED and a REDUCED
ENGINE POWER message in the Driver Information
Center on the instrument panel. See
Driver Information
Center (DIC) on page 3-55.
Overheated Engine Protection
Operating Mode (V8 Engines Only)
If an overheated engine condition exists and the
REDUCED ENGINE POWER message is displayed, an
overheat protection mode which alternates ®ring 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.
Notice: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 on page 5-18.
5-36

Tire Inspection and Rotation
Tires should be rotated every 5,000 to 8,000 miles
(8 000 to 13 000 km).
Any time you notice unusual wear, rotate your tires as
soon as possible and check wheel alignment. Also
check for damaged tires or wheels. See
When It Is Time
for New Tires on page 5-88andWheel Replacement
on page 5-92for more information.
Make sure the spare tire is stored securely. Push, pull,
and then try to rotate or turn the tire. If it moves,
use the wheel wrench/hoist shaft to tighten the cable.
See
Changing a Flat Tire on page 5-96.
If your vehicle has dual rear wheels, also see
Dual Tire
Operation on page 5-85.
The purpose of regular rotation is to achieve more
uniform wear for all tires on the vehicle. The ®rst rotation
is the most important. See
Scheduled Maintenance
on page 6-4, for scheduled rotation intervals.If your vehicle has single rear wheels and the tread
design for your front tires is the same as your rear tires,
use the rotation pattern shown here when rotating
your tires.
5-86

Tire Chains
{CAUTION:
If your vehicle has dual wheels or P265/75R16,
LT265/75R16 or P265/70R17 size tires, don't
use tire chains. They can damage your vehicle
because there's not enough clearance. Tire
chains used on a vehicle without the
properamount of clearance can cause damage
to thebrakes, suspension or other vehicle
parts. Thearea damaged by the tire chains
could cause you to lose control of your vehicle
and you or others may be injured in a crash.
Use another type of traction device only if its
manufacturer recommends it for use on your
vehicle and tire size combination and road
CAUTION: (Continued)
CAUTION: (Continued)
conditions. Follow that manufacturer's
instructions. To help avoid damage to your
vehicle, drive slowly, readjust or remove the
device if it's contacting your vehicle, and don't
spin your wheels.
If you do ®nd traction devices that will ®t,
install them on the rear tires.²
Notice:If your vehicle does not have dual wheels
and is equipped with a tire size other than
P265/75R16, LT265/75R16 or P265/70R17, use tire
chains only where legal and only when you
must. Use chains that are the proper size for your
tires. Install them on the tires of the rear axle. Don't
use chains on the tires of the front axle. Tighten
them as tightly as possible with the ends securely
fastened. Drive slowly and follow the chain
manufacturer's instructions. If you can hear the
chains contacting your vehicle, stop and retighten
them. If the contact continues, slow down until
it stops. Driving too fast or spinning the wheels with
chains on will damage your vehicle.
5-94

4. Make sure the jack head is positioned so that the
rear axle is resting securely between the grooves
that are on the jack head. Turn the wheel
wrench clockwise to raise the vehicle. Raise the
vehicle far enough off the ground so there is enough
room for the spare tire to ®t under the wheel well. Front Position All Other Models
Rear Position
5-104