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STARTING AND OPERATING 165
DRIVE (D)
This range should be used for most city and
highway driving. It provides the smoothest
upshifts and downshifts, and the best fuel
economy. The transmission automatically
upshifts through all forward gears.
When frequent transmission shifting occurs
(such as when operating the vehicle under
heavy loading conditions, in hilly terrain,
traveling into strong head winds, or while towing
a heavy trailer), select TOW/HAUL mode or use
the Electronic Range Select (ERS) shift control
to select a lower gear range Ú page 161. Under
these conditions, using a lower gear range will
improve performance and extend transmission
life by reducing excessive shifting and heat
build-up.
If the transmission temperature exceeds
normal operating 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 addi-
tional heat load on the cooling system. Down-
shifting 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 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 Ú page 168. On
Pickup models with 68RFE 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 AS69RC
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 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 FOURTH gear (for
68RFE transmission) or THIRD gear (for
AS69RC transmission) regardless of which
forward gear is selected. If an
AS69RC-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,
4
21_DJD2_OM_EN_USC_t.book Page 165
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