Functional Description - Transmission Control Module (TCM)

The TCM determines if the following conditions are met to perform an ESS auto-stop event:

• The TCM receives a CAN-C bus message from the PCM that indicates that there is an ESS auto-stop event pending and that the engine itself is ready for the ESS auto-stop event.
• The TCM receives a Electronic Stability Program (ESP) or an Electronic Stability Control (ESC) derived CAN-C bus message from the ABS module which indicates the vehicles speed threshold over a calibrated frame of time.
• The TCM determines that the transmission is not in R  everse or that the there is not a TCM SNA error. The TCM needs to see that either a forward gear is engaged or that the transmission is in N  eutral.
• The TCM determines if there are any DTCs on the transmission which can inhibit the ESS auto-stop. If a fault is detected, the TCM busses a fault CAN-C bus message back to the PCM. If no fault is detected, the TCM will bus a no fault CAN-C bus message to the PCM.
• The TCM then determines if it can allow the transmission into P  ark or N  eutral.
• The TCM then determines if the PCM CAN-C bus received message indicates that the engine is ready or is not ready for an ESS. A true CAN-C bus message attribute indicates that the CAN-C bus message received from the PCM does indicate that the engine is ready for an ESS event.
• Once the TCM verifies that the CAN-C bus message received from the PCM indicates that the engine is ready for an ESS auto-stop event, the TCM sends a CAN-C bus message back to the PCM indicating that the transmission is prepared and ready for an ESS auto-stop event to occur.
• The TCM then holds the "ready for ESS auto-stop event = True" state during the actual auto-stop event.
• During the actual ESS auto-stop event, the TCM indicates that the transmission is in a pseudo drive hydraulic neutral gear known as D6 and sends a CAN-C bus message to the PCM advising that the transmission is in a neutral state. This D6 gear state is also indicative of the transmission being in an open transmission torque path. D6 must be achieved prior to engaging the starter motor in response to a driver start request. The TCM busses a message indicating the drive state of the transmission being open or not open.

The TCM determines if the following conditions are met to perform an ESS auto-start event:

• The PCM sends a CAN-C network bussed message to the TCM indicating that there is an active request to start the engine.
• If the transmission equipped in this vehicle is equipped with a Hydraulic Impulse Storage (HIS) solenoid, the HIS is released when a CAN-C network bus message from the PCM indicates that the engine is starting.
• The PCM then starts the engine.
• The TCM then engages the appropriate gear.

TCM reaction to a driver departure condition - The TCM can secure the vehicle by shifting into P  ark if there is a recognized driver departure. The PCM monitors DPDM conditions that indicate driver departure, and if the PCM determines this to be true, the PCM sends a CAN-C network bus message to the TCM requesting that the TCM shift to P  ark. At this time, the TCM must place the transmission into the P  ark position.