Transmission Control Module (TCM): Notes

The Transmission Control Module (TCM) is the controlling unit for all electronic operations of the transaxle. The TCM receives information regarding vehicle operation from both direct and indirect inputs, and selects the operational mode of the transaxle. 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 communication bus.

Direct Inputs

• 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).

Indirect Inputs

• 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 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.

Direct Outputs

• Transmission Control Relay.
• Solenoids (LR/CC, 2/4, OD and UD).
• Vehicle Speed (to PCM).
• Torque Reduction Request (to PCM).

Indirect Outputs

• 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 responsibilities and functions. First, storing and maintaining Clutch Volume Indices (CVI). Next, storing and selecting appropriate Shift Schedules. Third, system self-diagnostics. Finally, diagnostic capabilities (with DRB(R) scan tool).