Page 236 of 532

Air Conditioning with Dual Zone Temperature
Control — If Equipped
With the Dual Zone Temperature Control System, each
front seat occupant can independently control the tem-
perature of air coming from the outlets on their side of
the vehicle. Air Conditioning and Heating Operation
To turn on the Air Conditioning, set the fan control at any
speed and press the snowflake button located on the
control panel. Conditioned air will be directed through
the outlets selected by the mode control. A light in the
snowflake button shows that the air conditioning is on.
Press the button a second time to turn the air condition-
ing off.
A/C Pushbutton
With the fan control in the ON posi-
tion, pushing the A/C button turns on
the air conditioning compressor. An
indicator light on the button shows
that the Air Conditioning compressor
is on. Conditioned air is now directed
through the mode outlets selected.
Pushing the button a second time turns the compressor
OFF.Dual Zone Control Head236 UNDERSTANDING YOUR INSTRUMENT PANEL
Page 241 of 532

Regular cleaning of the inside of the windows with a
non-filming cleaning solution (vinegar and water works
very well) will help prevent contaminates (cigarette
smoke, perfumes, etc.) from sticking to the windows.
Contaminates increase the rate of window fogging.
Summer Operation
Air conditioned vehicles must be protected with a high
quality antifreeze coolant during summer to provide
proper corrosion protection and to raise the boiling point
of the coolant for protection against overheating. A 50 %
concentration is recommended. Refer to Recommended
Fluids and Genuine Parts for the proper coolant type.
When using the air conditioner in extremely heavy traffic
in hot weather especially when towing a trailer, addi-
tional engine cooling may be required. If this situation is
encountered, operate the transmission in a lower gear to
increase engine RPM, coolant flow and fan speed. When stopped in heavy traffic, it may be necessary to shift into
NEUTRAL and depress the accelerator slightly for fast
idle operation to increase coolant flow and fan speed.
NOTE: On models equipped with Diesel engines, the
idle speed will automatically increase to 1000 rpm at
elevated coolant temperatures to improve engine cooling.
Your air conditioning system is also equipped with an
automatic recirculation system. When the system senses
a heavy load or high heat conditions, it may use partial
Recirculation A/C mode to provide additional comfort.
Winter Operation
When operating the system during the winter months,
make sure the air intake, located directly in front of the
windshield, is free of ice, slush, snow, or other obstruc-
tions. UNDERSTANDING YOUR INSTRUMENT PANEL 241
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Page 244 of 532

▫ Operating Precautions ..................263
▫ Cooling System Tips — Automatic Transmission 263
Engine Block Heater — If Equipped .........265
Diesel Exhaust Brake (Engine Braking) – If
Equipped ............................265
Automatic Transmission ..................266
▫ Automatic Transmission With Overdrive (5 Speed
545RFE) — If Equipped .................267
▫ Automatic Transmission (6 Speed AS68RC) — If
Equipped ...........................273
Manual Transmission ....................279
▫ Manual Transmission — 6 Speed (G56) ......280
▫ Recommended Vehicle Shift Speeds ........280
▫ Downshifting – Gas Engine ..............281 ▫ Downshifting – Diesel Engine ............282
Four-Wheel- Drive Operation — If Equipped . . . 283
▫ Manually Shifted Transfer Case Operating
Information/Precautions ................283
▫ Shifting Procedure - Manually Shifted Transfer
Case ..............................286
▫ Transfer Case Reminder Light ............287
▫ Electronically Shifted Transfer Case Operating
Information/Precautions (4 Position Switch)—If
Equipped ...........................288
▫ Shifting Procedure - Electronically Shifted Transfer
Case ..............................292
Limited-Slip Differential — If Equipped .......295
Power Take Off Operation – If Equipped ......296
▫ Stationary Mode ......................296244 STARTING AND OPERATING
Page 246 of 532

Snow Tires ...........................324
Tire Rotation Recommendations ............325
▫ Dual Rear Wheels .....................326
Engine Runaway .......................327
Fuel Requirements ......................327
▫ Fuel Requirements (Gas Engines) ..........327
▫ Fuel Requirements (6.7L Diesel Engines) .....331
Adding Fuel ..........................333
▫ Adding Fuel (Gas Engines) ..............333
▫ Adding Fuel (Diesel Engines) .............335
Vehicle Loading ........................338
▫ Certification Label .....................338
TrailerTowing .........................341 ▫ Common Towing Definitions .............341
▫ Trailer Hitch Classification ...............345
▫ Trailer Towing Weights (Maximum Trailer Weight
Ratings) ............................346
▫ Trailer And Tongue Weight ..............346
▫ Towing Requirements ..................347
▫ TowingTips .........................352
▫ Trailer Towing Mirrors — If Equipped ......354
Snowplow ............................355
▫ Before Plowing .......................356
▫ Snowplow Prep Package Model Availability . . 357
▫ Over The Road Operation With Snowplow
Attached ...........................358
▫ Methods For Removing Snow ............358246 STARTING AND OPERATING
Page 253 of 532

a manual transmission. Models with manual transmis-
sion are equipped with a clutch interlocking cranking
system. The clutch must be fully depressed to start the
vehicle.
3. Turn the ignition key to the ON position and look at
the instrument panel cluster lamps.
CAUTION!If WATER IN FUEL indicator light remains on DO
NOT START engine before you drain water from the
fuel filter to avoid engine damage. See Section 7 —
Maintaining Your Vehicle, for water drain proce-
dures.
4. Turn the ignition key to START and crank the engine.
Do not press the accelerator during starting. CAUTION!Do not crank engine for more than 15 seconds at a
time as starter motor damage may result. Turn key to
OFF and wait at least two minutes before trying
again.
5. When the engine starts, release the key.
6. Check to see that there is oil pressure.
7. Release the parking brake.
Starting Procedure — Engine Manifold Air
Temperature Below 66°F (19°C)
NOTE: The temperature displayed on the overhead
console (if equipped) does not necessarily reflect the
engine manifold air temperature. When certain engine
temperatures fall below 66°F (19°C) the lamp will remain
on indicating the intake manifold heater system is active. STARTING AND OPERATING 253
5
Page 266 of 532

NOTE: For optimum braking power it is recommended
to use the Exhaust Brake while in Tow/Haul Mode.
The purpose of the exhaust brake (engine braking) fea-
ture is to supply negative (braking) torque to the engine.
Typically, the engine braking is used for, but not limited
to, vehicle towing applications where vehicle braking can
be achieved by the internal engine power, thereby spar-
ing the mechanical brakes of the vehicle.
Benefits of the exhaust brake are:
• vehicle driving control
• reduced brake fade
• longer brake life
• faster cab warm-up. AUTOMATIC TRANSMISSION
CAUTION!Damage to the transmission may occur if the follow-
ing precautions are not observed:
• Shift into PARK only after the vehicle has come to
a complete stop.
• Shift into or out of REVERSE only after the
vehicle has come to a complete stop and the
engine is at idle speed.
• Do not shift from REVERSE, PARK, or NEUTRAL
into any forward gear when the engine is above
idle speed.
• Before shifting into any gear, make sure your foot
is firmly on the brake pedal.266 STARTING AND OPERATING
Page 269 of 532

“N” Neutral
Shift to Neutral when the vehicle is standing for pro-
longed periods with the engine running. The engine may
be started in this range. Set the parking brake if you must
leave the vehicle.
“D” Drive
This position provides all forward gears, including 3rd
gear direct and 4th or 5th gear overdrive (see Overdrive
Operation). Use this range for most city and highway
driving.
“2” Second
Use this position for driving slowly in heavy city traffic
or on mountain roads where more precise speed control
is desirable. Use it also when climbing long grades, and
for engine braking when descending moderately steep
grades. To prevent excessive engine speed do not exceed
45 mph (72 km/h) in this range. “1” First
Use this position for driving up very steep hills and for
engine braking at low speeds 20 mph (32 km/h) or less
when going downhill. To prevent excessive engine speed,
do not exceed 25 mph (40 km/h) in this range.
NOTE: Use caution when operating a heavily loaded
vehicle in “2” Second or “1” First gear selections in high
ambients as torque converter slip can impose significant
additional heat load on the cooling system.
Overdrive Operation
The overdrive automatic transmission contains an elec-
tronically controlled fourth and fifth speed (Overdrive).
The transmission will automatically shift from Drive to
Overdrive if the following conditions are present:
• the transmission selector is in Drive;
• the engine coolant has reached normal operating tem-
perature; STARTING AND OPERATING 269
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Page 271 of 532

When To Use “TOW HAUL” and “O/D OFF”
Modes
When driving in hilly areas, towing a trailer, carrying a
heavy load, etc., and frequent transmission shifting oc-
curs, press the “TOW HAUL O/D OFF” button once to
select TOW HAUL. This will improve performance and reduce the potential for transmission overheating or
failure due to excessive shifting. When operating in
“TOW HAUL” mode, 5th gear is disabled and 2-3 and 3-4
shift patterns are modified. Shifts into Overdrive (4th
gear) are allowed during steady cruise (for improved fuel
economy) and automatic closed-throttle downshifts to
3rd gear (for improved braking) will occur during steady
braking. Pressing the “TOW HAUL O/D OFF” button a
second time to select O/D OFF will disable 4th and 5th
gear completely, which should eliminate any excessive
transmission shifting.
The “TOW HAUL” or “O/D OFF” light will illuminate in
the instrument cluster to indicate when the switch has
been activated. Pressing the switch a third time restores
normal operation. If the “TOW HAUL” or “O/D OFF”
modes are desired, the button must be pressed each time
the engine is started.Tow Haul O/D Off Switch STARTING AND OPERATING 271
5