Transmission Control Module: Operation: Notes

The Transmission Control Module (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 vehicle communication 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
• 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(R) 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:

• 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 responsibilities and functions:

• Storing and maintaining Clutch Volume Indexes (CVI)
• Storing and selecting appropriate Shift Schedules
• System self-diagnostics
• Diagnostic capabilities (with DRBIII(R) scan tool)