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 sig-
nificant additional 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 tempera-
ture as well as vehicle speed. This feature improves warm
up time of the engine and transmission to achieve maxi-
mum 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 sec-
tion). 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 transmis-
sion, 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 ab-
normal 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, 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 damag-
ing 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.
146 STARTING AND OPERATING
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