1999 GMC C-SERIES ECU

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4-30
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.
NOTICE:
Your warranty does not cover parts or
components that fail because of overloading.
If you put things inside your vehicle -- like suitcases,
tools, packages or anything else
-- they will 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.

Don't leave an unsecured child restraint in
your vehicle.

When you carry something inside the
vehicle, secure it whenever you can.
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5-10
CAUTION:
To help avoid injury to you or others:

Never let passengers ride in a vehicle that is
being towed.

Never tow faster than safe or posted speeds.

Never tow with damaged parts not
fully secured.

Never get under your vehicle after it has
been lifted.

Always use separate safety chains on each
side when towing a vehicle.
If your vehicle uses dragfoilers, be sure to have the
dragfoiler
-to-cab mounting bracket bolts tightened after
your vehicle has been towed.
Here are specific towing instructions:
Towing Your Vehicle From the
Front (Front Wheels Off the Ground)
Before Towing
Block the rear wheels of the disabled vehicle. On
vehicles with air brakes, release the emergency brake
system by compressing the brake chamber springs as
outlined in this section. (Note: This is to prevent the
possibility of the emergency brake being applied
during towing.)
On vehicles with hydraulic brakes without an
electric/hydraulic parking brake, release the
parking brake fully by moving the lever to the
fully
-released position.
On vehicles equipped with an electric/hydraulic parking
brake option, remove the propshaft.
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5-12
Towing the Vehicle with the Front Bumper Installed
1. Connect and lock the lift chains to the front axle,
outside of the spring anchor plates as
previously shown.
2. Place a 6, x 6, x 5
hardwood beam underneath and
slightly behind the front spring shackle brackets as
previously shown.
3. Connect the lift chains to the tow bar and take up the
slack in the chains until the tow bar is within 4, of
the front bumper facing. Place a 2, x 12, x 40,
hardwood board with rubber pads against the front
bumper and secure as shown.
A. Rubber Pad
B. Hardwood Board
C. Shackle Bracket
D. Lift ChainE. Hardwood Beam
F. Bumper
G. Tow Bar
4. Remove the remaining slack in the lift chains.
The tow bar swing arm should rest against the
2, x 12, x 40, hardwood board as shown.
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5-13
A. Hardwood Board
B. Swing Arm
5. Raise the vehicle to the required height.Single Drive Rear Axle
Disconnect the propshaft at the rear axle. Secure the
propshaft to the frame or crossmember.
Tandem Drive Rear Axles
-- Forward Axle Off
the Ground
Raise the front of the vehicle until the forward
tandem axle wheels are off the ground. Remove the
rearward propshaft.
Tandem Drive Rear Axle
-- Both Axles on the
Ground Due to Type of Suspension or Attached Load
Disconnect the propshaft at the forward tandem axle.
Secure the propshaft to the frame or crossmember.
If there is damage or suspected damage to the axle(s),
remove all axle shafts. Cover the hub openings to
prevent the loss of lubricant or entry of dirt or
foreign objects.
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5-14
After Towing
Block the rear wheels and install axle and propeller
shafts. Check for proper phasing of universal joints.
Apply the emergency brake system before disconnecting
from the towing vehicle. Check and fill the rear axle
with oil as required.
Towing Your Vehicle From the Front
(All Wheels On the Ground)
Your vehicle may be towed on all wheels provided the
steering is working. Remember that the power brakes
and power steering will not have power assist. Vehicles
with air brakes will not have brakes. There must be a
tow bar installed between the towing vehicle and the
disabled vehicle.
Before Towing
Block the wheels of the disabled vehicle. On vehicles
with air brakes, release the emergency brake system by
compressing the brake chamber springs as outlined in
this section. (Note: This is to prevent the possibility of
the emergency brake being applied during towing.)On vehicles with hydraulic brakes, release the
parking brake fully by moving the lever to the
fully
-released position.
On vehicles equipped with an electric/hydraulic parking
brake, remove the propshaft.
Disconnect the propshaft at the rear axle (forward axle
on tandem axle models). Secure the propshaft to the
frame or crossmember.
If there is damage or suspected damage to the axle(s),
remove the axle shafts. Cover the hub openings to
prevent the loss of lubricant or entry of dirt or
foreign objects.
After Towing
Block the rear wheels and install axle and propshafts.
Check for proper phasing of universal joints. Apply
the parking brake system before disconnecting from
the towing vehicle. Check and fill rear axle with oil
as required.
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5-15 Towing Your Vehicle From the Rear
(Rear Wheels Off the Ground)
Before Towing
Secure the steering wheel to maintain a straight
-ahead
position. Make certain that the front axle is not loaded
above the front axle Gross Axle Weight Rating (GAWR)
as indicated on the vehicle's Certification/Tire label.
After Towing
Block the rear wheels and release the steering. Apply the
parking brake system before disconnecting from the
towing vehicle.
Refer to the transmission shift label for
additional information.
Releasing Air-Operated Parking Brakes
If your vehicle has air brakes, you could have a special
towing problem. If your vehicle has to be towed because
you had a complete loss of air pressure from both
systems, the parking brakes may have applied. The tow
operator can release the brakes manually by using the
following steps. Then your vehicle can be towed with all
wheels or just the rear wheels on the ground.
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7-19
(10) = Check clutch pedal for free travel. Press pedal
by hand until resistance is felt. Free travel should be
maintained at 1.5 to 2 inches (38 to 51 mm) measured
at the clutch pedal pad. Make checks at 3,000 miles
(5 000 km) and 6,000 miles (10 000 km) and then every
6,000 miles (10 000 km) thereafter.
(11) = Inspect rear axle air shift motor for fluid leaks.
Remove plug to check fluid level. Inspect air lines and
hoses for proper hook
-up, binding, leaks, etc. Inspect at
3,000 miles (5 000 km) and 24,000 miles (40 000 km)
and then every 24,000 miles (40 000 km) thereafter.
(12) = Chassis Lubrication Service: Lubricate all grease
fittings in front suspension, front axle and steering
linkage. DO NOT lubricate kingpin bushings with air
pressure equipment; instead, use a hand grease gun to
ensure complete purge and eliminate sealer cap
distortion. Lubricate transmission and shift linkage,
hood latches and hood hinges, parking brake lever pivot,
clevis pins and linkage, disc brake caliper rails, clutch
linkage and release bearing (if equipped), propeller shaft
slip joint, universal joint, brake camshaft bracket, slack
adjusters, pedal shaft, clutch cross shaft and clutch pedal
springs. Lubricate suspension, axle and steering linkage
more often when operating under dusty or muddy
conditions and in excessive off
-road use.(13) = Check steering system:

Look for damaged, loose or missing parts. Also
look for parts showing signs of wear or lack of
lubrication. Replace parts as needed. Also check
steering gear mounting bolts, pitman arm nut, gear
housing upper cover and side cover attaching bolts,
steering column mounting bolts and cardan
joint clamp bolts; tighten if necessary.
(See service manual.)

Inspect power steering hoses, tubes and fittings for
leaks. Hoses and lines must not be twisted, kinked or
tightly bent. Make sure clips, clamps, supporting
tubes and hoses are in place and properly secured.

Check steering gear for leakage around pitman shaft
and housing. If leakage is evident (lubricant
oozing out, not just oily film), leak should be
corrected immediately.
(14) = Check front and rear suspension. Look for
damaged, loose or missing parts or parts showing signs
of wear or lack of lubrication. Replace parts as needed.
(15) = Adjust tire pressures as indicated on the
Certification/Tire label for optimum tire life. See ªTiresº
in the Index for further details. Check tires for excessive
or abnormal wear or damage. Also check for damaged
wheels. Replace wheels and/or tires as needed.
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9-2
Brake (Continued)
Four-Wheel and Six-Wheel Drum 6-33 . . . . . . . . . . . . . . .
Four-Wheel Disc 6-32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hydraulic Systems 4-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Master Cylinder 6-30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parking 2-23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pedal Travel 6-33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Propshaft Brake Burnish Procedure 2-24 . . . . . . . . . . . . . . .
Releasing Air-Operated Parking Brakes 5-15 . . . . . . . . . . .
Replacing System Parts 6-35 . . . . . . . . . . . . . . . . . . . . . . . .
System Check 7-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Warning Lights 2-57 . . . . . . . . . . . . . . . . . . . . . . . .
Brake, Anti-Lock 4-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Braking 4-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Braking in Emergencies 4-9 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Break-In, New Vehicle 2-5 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Capacities and Specifications 6-74 . . . . . . . . . . . . . . . . . . . .
Carbon Monoxide 2-29, 2-30 , 4-27 . . . . . . . . . . . . . . . . . . .
Cassette Tape Player Care 3-12 . . . . . . . . . . . . . . . . . . . . . . . .
Center Passenger Position 1-22 . . . . . . . . . . . . . . . . . . . . . . . .
Certification/Tire Label 4-28, 6-67 . . . . . . . . . . . . . . . . . . . . .
Changing a Flat Tire 5-34 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Charging System Light 2-56 . . . . . . . . . . . . . . . . . . . . . . . . . .
Chassis Lubrication 6-37 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Check Gages Light 2-67 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checking Your Restraint Systems 1-36 . . . . . . . . . . . . . . . . . .
Chemical Paint Spotting 6-65 . . . . . . . . . . . . . . . . . . . . . . . . . . Child Restraints 1
-26 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Securing in the Center Seat Position 1-31 . . . . . . . . . . . . . .
Top Strap 1-30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cigarette Lighter 2-47 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Circuit Breaker Block, Instrument Panel 6-69 . . . . . . . . . . . . .
Cleaner, Air 6-17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cleaning
Fabric 6
-59 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glass 6-62 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inside of Your Vehicle 6-59 . . . . . . . . . . . . . . . . . . . . . . . . .
Instrument Panel 6-61 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Outside of Your Vehicle 6-63 . . . . . . . . . . . . . . . . . . . . . . . .
Safety Belts 6-61 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Special Problems 6-60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tires 6-64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vinyl 6-61 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Windshield and Wiper Blades 6-62 . . . . . . . . . . . . . . . . . . .
Clock, Setting the 3-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clutch Pedal Free Travel 6-37 . . . . . . . . . . . . . . . . . . . . . . . . .
Comfort Controls 3-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Component Box 6-44 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connections, Trailer 2-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control of a Vehicle 4-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Coolant 6-23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Heater, Engine 2-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recovery Tank 5-22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Surge Tank 5-29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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