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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 transmission, top overdrive gear
is also inhibited until the transmission fluid is warm, and
during extremely cold temperatures (-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 tempera-
tures (-4°F [-20°C] or below), operation 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.
410 STARTING AND OPERATING
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