Liberty 4WD V6-3.7L (2009)
Control Module: Description and Operation
Transmission Control Module - Operation
TRANSMISSION CONTROL MODULE - GASOLINE ENGINES
The TCM is the controlling unit for all electronic operations of the transmission. The TCM receives information regarding vehicle operation from both
direct and indirect inputs, and selects the operational mode of the transmission. Direct inputs are hard-wired to, and used specifically by the TCM.
Indirect inputs originate from other components/modules, and are shared with the TCM via the CAN bus.
Some examples of direct inputs to the TCM are:
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Battery (B+) voltage
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Ignition "ON" voltage
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Transmission Control Relay (Switched B+)
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Throttle Position Sensor
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Crankshaft Position sensor (CKP)
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Transmission Range Sensor (TRS)
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Pressure Switches (L/R, 2/4, OD)
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Transmission Temperature Sensor (TTS) (Integral to TRS)
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Input Shaft Speed Sensor
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Output Shaft Speed Sensor
Some examples of indirect inputs to the TCM are:
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Engine/Body Identification
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Manifold Pressure
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Target Idle
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Torque Reduction Confirmation
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Speed Control ON/OFF Switch
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Engine Coolant Temperature
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Ambient/Battery Temperature
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Brake Switch Status
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Scan Tool Communication
Based on the information received from these various 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:
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Transmission Control Relay
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Solenoids (L/R, 2/4, OD and UD)
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Vehicle Speed (to PCM)
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Torque Reduction Request (to PCM)
Some examples of TCM indirect outputs are:
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Transmission Temperature (to PCM)
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PRNDL Position (to CCN)
In addition to monitoring inputs and controlling outputs, the TCM has other important responsibilities and functions:
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Storing and maintaining Clutch Volume Indices (CVI)
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Storing and selecting appropriate Shift Schedules
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System self-diagnostics
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Diagnostic capabilities (with scan tool)
NOTE: If the TCM has been replaced, the "Quick Learn Procedure" must be performed. See: Powertrain Management/Computers and Control
Systems/Testing and Inspection/Programming and Relearning/TCM Quick Learn
CLUTCH VOLUME INDEX (CVI)
An important function of the TCM is to monitor Clutch Volume Index (CVI). CVIs represent the volume of fluid needed to compress a clutch pack.
The TCM monitors gear ratio changes by monitoring 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 Output Speed Sensor provides the TCM with output shaft speed information.
By comparing the two inputs, the TCM can determine transmission 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
