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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 be-
low), 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
accelerate under heavily loaded conditions may be re-
duced. 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 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 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.
3. Turn the ignition 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 diagnos-
tic equipment to determine if the problem could recur.
If the transmission cannot be reset, authorized dealer
service is required.
336 STARTING AND OPERATING
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