Theory Of Operation

The Transmission Control Module (TCM) can communicate with the Electronic Shift Module (ESM) on the Controller Area Network (CAN) or the Dedicated Powertrain (D-PT) CAN Bus. If the TCM loses communication with ESM the on the CAN C Bus it will continue to communicate with the ESM on the D-PT CAN Bus and set a DTC against the ESM for CAN C Bus off. If the TCM loses communication with the ESM on the CAN-DPT Bus it will continue to communicate with the ESM on the CAN C Bus and set a DTC against the ESM for D-PT CAN Bus off.

The purpose of the diagnostic is to monitor the D-PT CAN Bus, the transmitted messages on the CAN Bus and the validity of the D-PT CAN signals.

D-PT CAN Bus Monitoring:  To distinguish general problems with the D-PT CAN Bus (e.g. electrical problems) from problems with certain messages or signals, the general state of the D-PT CAN Bus is monitored.

D-PT CAN Message Monitoring:  All messages received and used by the Transmission Control Module (TCM) are monitored for timeout and validity of the Data Length Code (DLC) information in the message header. If available, the message is also monitored for the validity of a checksum and for the correct behavior of an alive-counter that the sending control unit is expected to increment on each transmittal.

D-PT CAN Signal Monitoring:  If the sending control unit does not have valid information to send, it may send a defined failure value indicating an invalid signal. Incoming signals with a defined failure value are monitored for signal validity.