SHIFT OUT OF NEUTRAL
The following steps describe the process for a shift out of NEUTRAL.
•
Extinguish the Neutral LED.
•
Engage the shift motor for a maximum of 1 second ±100 msec toward the transfer case 4LOCK mode position
while monitoring the mode sensor position.
•
Disengage the shift motor when the correct mode sensor position is recognized.
•
Extinguish the Neutral LED.
•
Transmit a bus message that the transfer case shift is complete.
•
If the desired mode sensor position is not received after the shift timer expires (i.e. a blocked or other condition
exists), stop driving the motor and wait for 200 msec ±50 msec. The shift motor is then reversed in the direc-
tion back toward the source gear for up to 1.0 seconds 100 msec. The FCM waits for 2.0 seconds ±50 msec.
and repeats the attempt to shift to the desired position.
•
When the Neutral button is released, if the 4LOCK position is the desired position, the shift is complete. Illu-
minate the 4LOCK message icon.
•
Otherwise when the Neutral button is released, if all of the shift requirements are being met then engage the
shift motor towards the desired position for 1 second ±100 msec per ’D’ channel. (if requirements for shifting
are not met, illuminate the 4LOCK message icon and flash the destination message icon as an indication to
the driver that all of the driver controllable shift conditions are not being met). If this requires another range or
mode shift, begin the range/mode shift process.
•
If the desired mode sensor position is not achieved after the shift timer expires (i.e. a blocked or other con-
dition exists), refer to the section on Blocked Shift Strategy, also known as Phase 2 shifts.
NEUTRAL BLOCKED SHIFT STRATEGY (PHASE 2 SHIFTS)
When a shift is commanded out of neutral, the shift motor will be driven towards its destination position, except in
the case of shifting out of NEUTRAL if 4LO was selected (the transfer case will shift to the 4LOCK position first,
before proceeding to 4LO). If the shift is blocked on the way to the destination, the FCM may attempt to drive the
motor back to the original position. This process will be allowed to occur 5 times. If the transfer case has reached
a non-NEUTRAL position during the shift re-attempts, the message icon for the achieved gear position is illuminated
and the shift attempts are stopped. To re-attempt the desired shift, the selector switch will need to be rotated to the
current position until the switch debounce timer expires then a shift will need to be requested again.
At the end of the 5th blocked attempt, the shift motor is driven towards the last known mode sensor position. If this
motor drive allows the transfer case to reach the AWD position, the shift is considered complete and the shift
attempts are ended.
If the mode sensor is in the NEUTRAL region at the expiration of the shift timer, the FCM will continue to make the
shift attempts according to the blocked shift strategy independent of whether or not the driver controlled conditions
are met.
For shifts from NEUTRAL, if all 5 attempts fail to reach the desired position (which by default is 4LOCK), the motor
will be driven to stall in the direction of 4LOCK or 4LO, depending on the achieved position. Otherwise, the transfer
case will be driven in the direction opposite the last attempt with the desired target being 4LOCK or 4LO.
If the transfer case reaches the AWD position when being driven in the 4LOCK direction, then one final 1.0 second
drive toward 4LOCK is attempted. If the transfer case then reaches the 4LOCK position, the shift is considered
complete and the 4LOCK message icon is illuminated. If the transfer case is still the AWD position, the shift is
considered complete and all message icons are extinguished.
NEUTRAL DRIFT SHIFT STRATEGY (PHASE 3 SHIFTS)
NOTE: If after the 5th blocked shift and reversal attempt, if the transfer case position is in the NEUTRAL or
other undesired region, shift attempts will continue until a non-NEUTRAL or a desired position is reached.
Phase 3 is a series of shifts whose intent is to escape from an undesired position that has been reached outside of
a shift. A perceived drift of the transfer case into a non-target region without the FCM driving the shift motor will
initiate a phase III shift. Phase 3 will be initiated by any non-target region with the exception of a position greater
then encoder_4LO_min or less then encoder_4LOCK_max. Whenever these encoder readings have been seen for
defined period of time, Phase III shifting will begin.
8E - 176
ELECTRONIC CONTROL MODULES - SERVICE INFORMATION
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