If the transmission temperature exceeds normal operat-
ing limits, the powertrain controller will modify the
transmission shift schedule and expand the range of
torque converter clutch engagement. This is done to
prevent transmission damage due to overheating.
If the transmission becomes extremely hot or is in danger
of overheating, the “Transmission Temperature Warning
Light” may illuminate and the transmission may operate
differently until the transmission cools down.
NOTE:Use caution when operating a heavily loaded
vehicle at low speeds (such as towing a trailer up a steep
grade, or in stop-and-go traffic) during hot weather. In
these conditions, torque converter slip can impose a
significant additional heat load on the cooling system.
Downshifting the transmission to the lowest possible
gear (when climbing a grade), or shifting to NEUTRAL
(when stopped in heavy traffic) can help to reduce this
excess heat generation. During cold temperatures, transmission operation may
be modified depending on engine and transmission
temperature as well as vehicle speed. This feature im-
proves warm up time of the engine and transmission to
achieve maximum efficiency. Engagement of the torque
converter clutch is inhibited until the transmission fluid
is warm (refer to the “Note” under “Torque Converter
Clutch” in this section). On models with 66RFE transmis-
sion, top overdrive gear is also inhibited until the trans-
mission fluid is warm, and during extremely cold tem-
peratures (-16°F [-27°C] or below), operation may briefly
be limited to first and direct gears only. On trucks with
AS66RC transmission, fifth and sixth gears may be
inhibited briefly on cold starts below 41°F (5°C), and
during very cold temperatures (-4°F [-20°C] or below),
operation may briefly be limited to third gear only.
During this condition, the ability of the vehicle to accel-
erate under heavily loaded conditions may be reduced.
306 STARTING AND OPERATING
In all cases, normal operation will resume once the
transmission temperature has risen to a suitable level.
Transmission Limp Home Mode
Transmission function is monitored electronically for
abnormal conditions. If a condition is detected that could
result in transmission damage, Transmission Limp Home
Mode is activated. In this mode, the transmission remains
in fourth gear (for 66RFE transmission) or third gear (for
AS66RC transmission) regardless of which forward gear
is selected. If an AS66RC equipped truck enters Limp
Home Mode at highway speeds, it will initially engage
fifth gear, until the vehicle slows to a speed where third
gear can be engaged. PARK, REVERSE, and NEUTRAL
will continue to operate. The Malfunction Indicator Light
(MIL) may be illuminated. Limp Home Mode allows the
vehicle to be driven to an authorized dealer for service
without damaging the transmission.In the event of a momentary problem, the transmission
can be reset to regain all forward gears by performing the
following steps:
1. Stop the vehicle.
2. Shift the transmission into PARK.
3. Turn the ignition switch to the OFF position.
4. Wait approximately 10 seconds.
5. Restart the engine.
6. Shift into the desired gear range. If the problem is no
longer detected, the transmission will return to normal
operation.
NOTE: Even if the transmission can be reset, we recom-
mend that you visit your authorized dealer at your
earliest possible convenience. Your authorized dealer has
diagnostic equipment to determine if the problem could
recur.
5
STARTING AND OPERATING 307
Proper operation of four-wheel drive vehicles depends
on tires of equal size, type and circumference on each
wheel. Any difference will adversely affect shifting and
can cause damage to the drivetrain.
NOTE:Do not attempt to make a shift while only the
front or rear wheels are spinning. The front and rear
driveshaft speeds must be equal for the shift to take
place. Shifting while only the front or rear wheels are
spinning can cause damage to the transfer case.
Because four-wheel drive provides improved traction,
there is a tendency to exceed safe turning and stopping
speeds. Do not go faster than road conditions permit.
NOTE: Delayed shifts out of four-wheel drive may be
experienced due to uneven tire wear, low or uneven tire
pressures, excessive vehicle loading, or cold tempera-
tures.WARNING!
You or others could be injured or killed if you leave
the vehicle unattended with the transfer case in the
NEUTRAL position without first fully engaging the
parking brake. The transfer case NEUTRAL position
disengages both the front and rear drive shafts from
the powertrain and will allow the vehicle to move
regardless of the transmission position. The parking
brake should always be applied when the driver is
not in the vehicle.
For additional information on the appropriate use of each
transfer case mode position, see the information below:
2H
Rear-Wheel Drive High Range — This range is for
normal street and highway driving on dry hard surfaced
roads.
5
STARTING AND OPERATING 313
4H
Four-Wheel Drive High Range — This range locks the
front and rear driveshafts together forcing the front and
rear wheels to rotate at the same speed. Additional
traction for loose, slippery road surfaces only.
Neutral (N)
Neutral — This range disengages the front and rear
driveshafts from the powertrain. To be used for flat
towing behind another vehicle. Refer to “Recreational
Towing” in “Starting and Operating” for further infor-
mation.
4L
Four-Wheel Drive Low Range — This range locks the
front and rear driveshafts together forcing the front and
rear wheels to rotate at the same speed. Additionaltraction and maximum pulling power for loose, slippery
road surfaces only. Do not exceed 25 mph (40 km/h).
CAUTION!
Do not use 4L (Low) range when operating the
vehicle on dry pavement. Driveline hardware dam-
age can result.
Shifting Procedure — Manually Shifted Transfer
Case
2H To 4H
Shifting between 2H and 4H can be made with the
vehicle stopped or in motion. If the vehicle is in motion,
shifts can be made up to 55 mph (88 km/h). With the
vehicle in motion, the transfer case will engage/
disengage faster if you momentarily release the accelera-
tor pedal after completing the shift. Apply a constant
force when shifting the transfer case lever.
314 STARTING AND OPERATING
2H Or 4H To 4L
With the vehicle rolling at 2 to 3 mph (3 to 5 km/h), shift
the transmission into NEUTRAL. While the vehicle is
coasting at 2 to 3 mph (3 to 5 km/h), shift the transfer
case lever firmly to the desired position. Do not pause in
transfer case NEUTRAL.
NOTE:
•Pausing in transfer case NEUTRAL in vehicles
equipped with an automatic transmission may require
shutting the engine OFF to avoid gear clash while
completing the shift. If difficulty occurs, shift the
transmission into NEUTRAL, hold foot on brake, and
turn the engine OFF. Make shift to the desired mode.
• Shifting into or out of 4L is possible with the vehicle
completely stopped, however difficulty may occur due to the mating clutch teeth not being properly aligned.
Several attempts may be required for clutch teeth
alignment and shift completion to occur. The preferred
method is with the vehicle rolling 2 to 3 mph (3 to
5 km/h). Avoid attempting to engage or disengage 4L
with the vehicle moving faster than 2 to 3 mph (3 to
5 km/h).
• Do not attempt to shift into or from 4L while the
transmission is in gear.
Transfer Case Position Indicator Light
The “Transfer Case Position Indicator Light” in the
instrument cluster is used to alert the driver that the front
axle is fully engaged and all four wheels are driving.
5
STARTING AND OPERATING 315
and 4WD LOW positions are designed for loose, slippery
road surfaces only. Driving in the 4WD LOCK and 4WD
LOW positions on dry hard surfaced roads may cause
increased tire wear and damage to the driveline compo-
nents.
NOTE:The transfer case NEUTRAL position is selected
by pressing the button located on the lower left hand
corner of the 4WD Control Switch. The transfer case
NEUTRAL position is to be used for recreational towing
only. Refer to “Recreational Towing” in “Starting and
Operating” for further information.
Transfer Case Position Indicator Lights
The Transfer Case Position Indicator Lights (4WD and
4LOW) are located in the instrument cluster and indicate
the current and desired transfer case selection. When you
select a different transfer case position, the indicator
lights will do the following: If All Shift Conditions Are Met:
1. The current position indicator light will turn OFF.
2. The selected position indicator light will flash until the
transfer case completes the shift.
3. When the shift is complete, the indicator light for the selected position will stop flashing and remain ON.
If One Or More Shift Conditions Are Not Met:
1. The indicator light for the current position will remain ON.
2. The newly selected position indicator light will con- tinue to flash.
3. The transfer case will notshift.
NOTE: Before retrying a selection, make certain that all
the necessary requirements for selecting a new transfer
case position have been met. To retry the selection, turn
5
STARTING AND OPERATING 317
the control knob back to the current position, wait five
seconds, and retry selection. To find the shift require-
ments, refer to theShifting Procedure for your transfer
case, located in this section.
The “SVC 4WD Warning Light” monitors the electronic
shift four-wheel drive system. If this light remains on
after engine start up or illuminates during driving, it
means that the four-wheel drive system is not function-
ing properly and that service is required.
WARNING!
Always engage the parking brake when powering
down the vehicle if the “SVC 4WD Warning Light” is
illuminated. Not engaging the parking brake may
allow the vehicle to roll, which may cause personal
injury. NOTE:
Do not attempt to make a shift while only the
front or rear wheels are spinning, as this can cause
damage to driveline components.
When operating your vehicle in 4WD LOW, the engine
speed is approximately three times that of the 2WD or
4WD LOCK positions at a given road speed. Take care
not to overspeed the engine and do not exceed 25 mph
(40 km/h).
Proper operation of four-wheel drive vehicles depends
on tires of equal size, type and circumference on each
wheel. Any difference in tire size can cause damage to the
drivetrain.
Because four-wheel drive provides improved traction,
there is a tendency to exceed safe turning and stopping
speeds. Do not go faster than road conditions permit.
318 STARTING AND OPERATING
towing behind another vehicle. Refer to “Recreational
Towing” in “Starting and Operating” for further infor-
mation.
Shifting Procedure
NOTE:
•If any of the requirements to select a new transfer case
position have not been met, the transfer case will not
shift. The position indicator light for the previous
position will remain ON and the newly selected posi-
tion indicator light will continue to flash until all the
requirements for the selected position have been met.
To retry a shift: return the control knob back to the
original position, make certain all shift requirements
have been met, wait five seconds and try the shift
again. •
If all the requirements to select a new transfer case
position have been met, the current position indicator
light will turn OFF, the selected position indicator light
will flash until the transfer case completes the shift.
When the shift is complete, the position indicator light
for the selected position will stop flashing and remain
ON.
2WD To 4WD LOCK
Rotate the 4WD control switch to the desired position.
Shifts between 2WD and 4WD LOCK can be done with
the vehicle stopped or in motion. With the vehicle in
motion, the transfer case will engage/disengage faster if
you momentarily release the accelerator pedal after turn-
ing the control switch. If the vehicle is stopped, the
ignition switch must be in the ON position with the
engine either running or off. This shift cannot be com-
pleted if the ignition switch is in the ACC position.
320 STARTING AND OPERATING