Transmission Control Module - Gasoline Engines: Notes

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 PCI bus.

Some examples of direct inputs  to the TCM are:

1. Battery (B+) voltage
2. Ignition "ON" voltage
3. Transmission Control Relay (Switched B+)
4. Throttle Position Sensor
5. Crankshaft Position Sensor (CKP)
6. Transmission Range Sensor (TRS)
7. Pressure Switches (L/R, 2/4, OD)
8. Transmission Temperature Sensor (Integral to TRS)
9. Input Shaft Speed Sensor
10. Output Shaft Speed Sensor

Some examples of indirect inputs  to the TCM are:

1. Engine/Body Identification
2. Manifold Pressure
3. Target Idle
4. Torque Reduction Confirmation
5. Speed Control ON/OFF Switch
6. Engine Coolant Temperature
7. Ambient/Battery Temperature
8. Brake Switch Status
9. DRB(R) III 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:

1. Transmission Control Relay
2. Solenoids (L/R, 2/4, OD and UD)
3. Vehicle Speed (to PCM)
4. Torque Reduction Request (to PCM)

Some examples of TCM indirect outputs  are:

1. Transmission Temperature (to PCM)
2. PRNDL Position (to BCM)

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

1. Storing and maintaining Clutch Volume Indices (CVI)
2. Storing and selecting appropriate Shift Schedules
3. System self-diagnostics
4. Diagnostic capabilities (with DRB(R) III scan tool)