nate from other components/modules, and are shared
with the TCM via the PCI bus.
Some examples of direct inputs to the TCM are:
• Battery (B+) voltage
• Ignition “ON” voltage
• Transmission Control Relay (Switched B+)
• Throttle Position Sensor
• Crankshaft Position Sensor (CKP)
• Transmission Range Sensor (TRS)
• Pressure Switches (L/R, 2/4, OD)
• Transmission Temperature Sensor (Integral to
TRS)
• Input Shaft Speed Sensor
• Output Shaft Speed Sensor
• TRS Hall Effect Switch (Autostick)
Some examples of indirect inputs to the TCM
are:
• Engine/Body Identification
• Manifold Pressure
• Target Idle
• Torque Reduction Confirmation
• Speed Control ON/OFF Switch
• Engine Coolant Temperature
• Ambient/Battery Temperature
• Brake Switch Status
• DRB 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 (L/R, 2/4, OD and UD)
• Vehicle Speed (to PCM)
• Torque Reduction Request (to PCM)
Some examples of TCM indirect outputs are:
• Transmission Temperature (to PCM)
• PRNDL Position (to BCM)
• Autostick Display (to BCM)
In addition to monitoring inputs and controlling
outputs, the TCM has other important responsibili-
ties and functions:
• Storing and maintaining Clutch Volume Indices
(CVI)
• Storing and selecting appropriate Shift Sched-
ules
• System self-diagnostics
• Diagnostic capabilities (with DRB III scan tool)
NOTE: If the TCM has been replaced, the “Quick
Learn Procedure” must be performed. Refer to
“Quick Learn Procedure” in Service Procedures of
this group.
CLUTCH VOLUME INDEX (CVI)
An important function of the TCM is to monitor
Clutch Volume Index (CVI). CVIs represent the vol-
ume of fluid needed to compress a clutch pack.
The TCM monitors gear ratio changes by monitor-
ing the Input and Output Speed Sensors. The Input,
or Turbine Speed Sensor sends an electrical signal to
the TCM that represents input shaft rpm. The Out-
put Speed Sensor provides the TCM with output
shaft speed information.
By comparing the two inputs, the TCM can deter-
mine transaxle gear position. This is important to
the CVI calculation because the TCM determines
CVIs by monitoring how long it takes for a gear
change to occur (Fig. 15).
Gear ratios can be determined by using the DRB
Scan Tool and reading the Input/Output Speed Sen-
sor values in the “Monitors” display. Gear ratio can
be obtained by dividing the Input Speed Sensor value
by the Output Speed Sensor value.
For example, if the input shaft is rotating at 1000
rpm and the output shaft is rotating at 500 rpm,
then the TCM can determine that the gear ratio is
Fig. 14 Transmission Control Module Location
(Typical)
1 – PDC
2 – PCM
3 – TRANSMISSION CONTROL MODULE (TCM)
LH 42LE TRANSAXLE 21 - 11
DESCRIPTION AND OPERATION (Continued)
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