Dodge RAM 1500 1998 Owner's Manual page 426

DR
TRANSFER CASE CONTROL MODULE (Continued)
SHIFT REVERSAL TARGETS
If the shift timer expires (1 second per 'D' channel)
and the transfer case has not reached the desired
position, all shifts will attempt to return to their
original position with the exceptions of:
• If the intended shift is going to the High rail
from Low and can't make it, but it can make the
2WD/AWD position, the motor stops at that position.
The TCCM will not attempt to cross back over NEU-
TRAL if it does not have to. This means that there
was a block on the first attempt to go to 4H and the
transfer case has made it through NEUTRAL to a
known good position, then the motor will go back
only to the 2WD/4WD position and execute the
remainder of the attempts from there.
• For shifts out of NEUTRAL, any time a shift is
commanded out of NEUTRAL, the system needs to
get out. The TCCM should never go to NEUTRAL
unless the driver is commanding it and all required
conditions are being met
ENCODER DRIFT CORRECTION
Whenever a shift is completed, the TCCM stores
the position in memory as the transfer case's
intended position. The TCCM continuously monitors
the mode sensor and if the mode sensor drifts toward
into a NEUTRAL region sensor position for 2.0 sec-
onds, the TCCM will perform a motor drive to correct
the drift. The transfer case will be driven toward the
intended position for 1.0 seconds 100 msec. The
TCCM will wait for 2.0 seconds ±50 msec. and repeat
the attempt to shift to the desired position. This will
continue until the intended position is reached.
SHIFT MOTOR BRAKING
Two modes of shift motor braking are employed to
improve shift performance, static and dynamic. Static
shift motor braking is utilized under the following
conditions:
• Whenever the transfer case is in the 2WD/AWD
or 4L 'D' channel position.
ELECTRONIC CONTROL MODULES
• Whenever an invalid mode sensor code is
present.
Static motor braking is achieved by applying +12V
on both shift motor wires.
NOTE: Static Shift Motor Braking is independent of
ignition key position.
SHIFT ATTEMPT LIMIT
To protect the transfer case system, the TCCM will
impose a limit on the number of shifts that can occur
over a calibrated time period. The system will moni-
tor the number of 'D' channel segment transitions
that occur in any 30 second time period. If the num-
ber of segment transitions is 30 or greater, the sys-
tem will go into a default mode. The default mode of
operation for shifting is that the number of allowed
'D' channel transitions permitted to occur will be 3
over each 15 second ±100 msec calibrated window of
time. After 5 minutes ±100 msec, the motor can be
assumed to have cooled down and the system will
revert to normal operation. The following rules also
apply to the shift limit:
• The attempt limit will not prevent shifts coming
out of NEUTRAL, they will be allowed regardless of
the counter/timer.
• Any shift that is in progress when the counter
reaches a maximum count in time will be allowed to
complete before the default mode is entered. D-chan-
nel transitions during this period will not be counted
towards the default mode limit.
• A block, regardless of the direction, whether
towards destination or back towards reversal target
(shift timer expiring), will count as a value of 2 tran-
sitions towards the 30 segment transitions to go into
default mode as defined above. Current attempt limit
values are 30 transitions in 30 seconds and default
mode values are 3 transitions every 15 seconds for 5
minutes.
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