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DR
TRANSFER CASE CONTROL MODULE (Continued)
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 monitor
the number of 'D' channel segment transitions that
occur in any 30 second time period. If the number of
segment transitions is 30 or greater, the system will go
into a default mode. The default mode of operation for
shifting is that the number of allowed 'D' channel tran-
sitions 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.
TRANSMISSION CONTROL
MODULE
DESCRIPTION
The Transmission Control Module (TCM) (Fig. 10)
may be sub-module within the Powertrain Control
Module (PCM) or a standalone module, depending on
the vehicle engine. The PCM, and TCM when
equipped, is located at the right rear of the engine
compartment, near the right inner fender.
OPERATION
The Transmission Control Module (TCM) controls
all electronic operations of the transmission. The
TCM receives information regarding vehicle opera-
tion from both direct and indirect inputs, and selects
the operational mode of the transmission. Direct
inputs are hardwired to, and used specifically by the
TCM. Indirect inputs are shared with the TCM via
the vehicle communication bus.
Some examples of direct inputs to the TCM are:
• Battery (B+) voltage
• Ignition "ON" voltage
• Transmission Control Relay (Switched B+)
ELECTRONIC CONTROL MODULES
Fig. 10 PCM/TCM Location
1 - RIGHT FENDER
2 - TRANSMISSION CONTROL MODULE
3 - POWERTRAIN CONTROL MODULE
• Throttle Position Sensor
• Crankshaft Position Sensor
• Transmission Range Sensor
• Pressure Switches
• Transmission Temperature Sensor
• Input Shaft Speed Sensor
• Output Shaft Speed Sensor
• Line Pressure Sensor
Some examples of indirect inputs to the TCM are:
• Engine/Body Identification
• Manifold Pressure
• Target Idle
• Torque Reduction Confirmation
• Engine Coolant Temperature
• Ambient/Battery Temperature
• DRBIII Scan Tool Communication
Based on the information received from these var-
ious inputs, the TCM determines the appropriate
shift schedule and shift points, depending on the
present operating conditions and driver demand.
This is possible through the control of various direct
and indirect outputs.
Some examples of TCM direct outputs are:
• Transmission Control Relay
• Solenoids
• Torque Reduction Request
Some examples of TCM indirect outputs are:
• Transmission Temperature (to PCM)
• PRNDL Position (to BCM)
In addition to monitoring inputs and controlling
outputs, the TCM has other important responsibili-
ties and functions:
• Storing and maintaining Clutch Volume Indexes
(CVI)
• Storing and selecting appropriate Shift Schedules
• System self-diagnostics
• Diagnostic capabilities (with DRBIII scan tool)
8E - 19
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