Module, Transmission Control (TCM): Operation

The Transmission Control Module (TCM) regulates the amount of hydraulic pressure used to engage the clutches and the Torque Converter Clutch (TCC), in addition to directing hydraulic pressure to engage or release any given clutch for any given required gear.

The TCM will actuate the valves by using solenoids based on the position of the shifter, transmission fluid temperature, engine operating conditions, traction conditions and driver demands.

During a shift, the TCM will actuate the solenoids to match the gear ranges to the optimal torque range of the engine based on the position of the accelerator pedal, shifter and vehicle speed as determined by the Powertrain Control Module (PCM) based on input from the Vehicle Speed Sensor (VSS) and Antilock Brake System (ABS) module.

Some examples of direct inputs  to the TCM are:

• Battery (B+) voltage
• Ignition Status
• Transmission Range Sensor (TRS)
• Cruise Control Switch
• Throttle Position
• Body Control Module (BCM)
• Shifter Position
• Pressure Switches
• Transmission Temperature Sensor
• Input Speed Sensor (ISS)
• Output Speed Sensor (OSS)
• Line Pressure Sensor

Some examples of indirect inputs  to the TCM are:

• Torque Reduction Confirmation
• Engine Coolant Temperature (ECT)
• Diagnostic 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:

• Solenoids
• Torque Reduction Request

Some examples of TCM indirect outputs  are:

• Transmission Temperature
• PRNDL Position

In addition to monitoring inputs and controlling outputs, the TCM has other important responsibilities and functions:

• Storing and Selecting Appropriate Shift Schedules
• System Self-diagnostics
• Diagnostic Capabilities (with scan tool)