1999 GMC YUKON climate control

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2-29
The transfer case switches are below and to the left of
the climate controls. Use these switches to shift into and
out of four
-wheel drive. You can choose among four
driving settings:
2HI: This setting is used for driving in most situations.
Your front axle is not engaged in two
-wheel drive. This
setting also provides the best fuel economy.
AUTO 4WD: This setting is ideal for use when road
conditions are variable. When driving your vehicle in
AUTO 4WD, the front axle is engaged, but the vehicle'spower is sent only to the rear wheels. When the vehicle
senses a loss of traction, the system will automatically
engage four
-wheel drive. Driving in this mode results in
lower fuel economy than 2HI.
4HI: Use 4HI when you need extra traction, such as on
snowy or icy roads or in most off
-road situations. This
setting also engages your front axle to help drive
your vehicle.
4LO: This setting also engages your front axle and
delivers extra torque. You may never need 4LO. It sends
maximum power to all four wheels. You might choose
4LO if you are driving off
-road in deep sand, deep mud,
deep snow and climbing or descending steep hills.
CAUTION:
Shifting the transfer case to NEUTRAL can
cause your vehicle to roll even if the transmission
is in PARK (P). You or someone else could be
seriously injured. Be sure to set the parking
brake before placing the transfer case in
NEUTRAL. See ªParking Brakeº in the Index.

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6-44 Uniform Tire Quality Grading
The following information relates to the system
developed by the United States National Highway
Traffic Safety Administration, which grades tires by
treadwear, traction and temperature performance. (This
applies only to vehicles sold in the United States.) The
grades are molded on the sidewalls of most passenger
car tires. The Uniform Tire Quality Grading system does
not apply to deep tread, winter
-type snow tires,
space
-saver or temporary use spare tires, tires with
nominal rim diameters of 10 to 12 inches (25 to 30 cm),
or to some limited
-production tires.
While the tires available on General Motors passenger
cars and light trucks may vary with respect to these
grades, they must also conform to Federal safety
requirements and additional General Motors Tire
Performance Criteria (TPC) standards.
Treadwear
The treadwear grade is a comparative rating based on
the wear rate of the tire when tested under controlled
conditions on a specified government test course. For
example, a tire graded 150 would wear one and a half
(1 1/2) times as well on the government course as a tire
graded 100. The relative performance of tires dependsupon the actual conditions of their use, however, and
may depart significantly from the norm due to variations
in driving habits, service practices and differences in
road characteristics and climate.
Traction
-- AA, A, B, C
The traction grades, from highest to lowest, are AA, A,
B, and C. Those grades represent the tire's ability to stop
on wet pavement as measured under controlled
conditions on specified government test surfaces of
asphalt and concrete. A tire marked C may have poor
traction performance. Warning: The traction grade
assigned to this tire is based on straight
-ahead braking
traction tests, and does not include acceleration,
cornering, hydroplaning, or peak traction characteristics.
Temperature
-- A, B, C
The temperature grades are A (the highest), B, and C,
representing the tire's resistance to the generation of
heat and its ability to dissipate heat when tested under
controlled conditions on a specified indoor laboratory
test wheel. Sustained high temperature can cause the
material of the tire to degenerate and reduce tire life, and
excessive temperature can lead to sudden tire failure.
The grade C corresponds to a level of performance
which all passenger car tires must meet under the

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9-2
Brake (Continued)
Replacing System Parts 6-32 . . . . . . . . . . . . . . . . . . . . . . . .
System Warning Light 2-74 . . . . . . . . . . . . . . . . . . . . . . . . .
Trailer 4-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transmission Shift Interlock Check 7-37 . . . . . . . . . . . . . . .
Wear 6-31 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Brakes, Anti-Lock 4-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Braking 4-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Braking in Emergencies 4-9 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Break-In, New Vehicle 2-20 . . . . . . . . . . . . . . . . . . . . . . . . . .
Brightness Control 2-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BTSI Check 7-37 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bulb Replacement 6-34, 6-61 . . . . . . . . . . . . . . . . . . . . . . . . .
Canadian Roadside Assistance 8-7 . . . . . . . . . . . . . . . . . . . .
Capacities and Specifications 6-63 . . . . . . . . . . . . . . . . . . . . . .
Carbon Monoxide 2-11, 2-36, 2-37, 4-41, 4-48, 4-49 . . . . .
Cargo Security Shade 2-58 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cargo Tie Downs 2-59 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cassette Deck Service 7-35 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cassette Tape Player 3-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cassette Tape Player Care 3-22 . . . . . . . . . . . . . . . . . . . . . . . .
Cassette Tape Player Errors 3-11 . . . . . . . . . . . . . . . . . . . . . . .
CD Changer 3-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cellular Telephone 2-67 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Center High-Mounted Stoplamp Bulb Replacement 6-37 . . . .
Center Passenger Position 1-36 . . . . . . . . . . . . . . . . . . . . . . . .
Certification/Tire Label 4-43 . . . . . . . . . . . . . . . . . . . . . . . . . .
Chains, Safety 4-48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chains, Tire 6-46 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Changing a Flat Tire 5-19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Charging System Warning Light 2-73 . . . . . . . . . . . . . . . . . . .
Check Gages Light 2-81 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Checking Your Restraint Systems 1
-57 . . . . . . . . . . . . . . . . . .
Chemical Paint Spotting 6-53 . . . . . . . . . . . . . . . . . . . . . . . . . .
Child Restraints 1-41 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Securing in a Rear Outside Seat Position 1-48 . . . . . . . . . . .
Securing in the Center Rear Seat Position 1-50 . . . . . . . . . .
Securing in the Right Front Seat Position 1-52 . . . . . . . . . .
Top Strap 1-46 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Where to Put 1-45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cigarette Lighter 2-61 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Circuit Breakers and Fuses 6-57 . . . . . . . . . . . . . . . . . . . . . . .
Cleaner, Air 6-15, 6-64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cleaning
Aluminum Wheels 6
-52 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exterior Lamps/Lenses 6-51 . . . . . . . . . . . . . . . . . . . . . . . .
Fabric 6-47 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glass 6-50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inside of Your Vehicle 6-47 . . . . . . . . . . . . . . . . . . . . . . . . .
Instrument Panel 6-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interior Plastic Components 6-49 . . . . . . . . . . . . . . . . . . . . .
Leather 6-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Outside of Your Vehicle 6-51 . . . . . . . . . . . . . . . . . . . . . . . .
Speaker Covers 6-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Special Problems 6-48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stains 6-48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tires 6-52 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vinyl 6-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wheels 6-52 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Windshield and Wiper Blades 6-50 . . . . . . . . . . . . . . . . . . .
Wood Panels 6-49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Climate Control System 3-2 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock, Setting the 3-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comfort Controls 3-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comfort Guides, Rear Safety Belts 1-34 . . . . . . . . . . . . . . . . .