Transmission Control Module (TCM)

The TCM receives inputs from the PCM for cruise control operation and performs requested down and up shifts when commanded.

When the vehicle is in manual shift mode, the transmission will not shift due to requests by the cruise system unless the transmission requires an upshift for the protection of powertrain components. For the vehicles equipped with transmission autostick or Electronic Range Selection (ERS) mode, the cruise system will not prevent the transmission from being manually shifted. The priority of different gear change requests is managed by TCM.

The cruise Resume function allows immediate downshifts based on current speed when the cruise Resume switch is pressed, by forcing a series of downshifts if the driver presses the Resume button and the vehicle is moving below the cruise control set speed. This will give the vehicle better acceleration to reach the set speed when the Resume button is pressed

Under downhill conditions, the PCM may require a transmission gear different from that selected by the transmission shift map, to maintain the cruise set speed. In these conditions, the PCM will transmit a maximum gear request to limit the operating range of the transmission. The transmission then will determine if selecting the maximum gear requested by the PCM can be honored, or would result in an engine overspeed condition, therefore not honoring the request from the PCM.

Inputs

• Presence of the cruise control system which indicates to the TCM that cruise is present on the vehicle
• Cruise control system operating state from the PCM
• Cruise set speed from the PCM over the CAN-C bus. This is to prevent unnecessary shifting
• Downshift request from the PCM over the CAN-C bus

Outputs

• Outputs the current transmission gear to the PCM
• Responds to gear change requests from the PCM
• Indication of Limp Mode to the PCM