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STARTING AND OPERATING 261
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 tempera-
ture as well as vehicle speed. This feature improves 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 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), oper-
ation may briefly be limited to third gear only. During this
condition, the ability of the vehicle to accelerate under
heavily loaded conditions may be reduced. 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
third gear 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 trans-
mission.
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 OFF.
4. Wait approximately 10 seconds.
5
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