Principles of Operation: Notes

The vehicle has 3 module communications networks:

• controller area network (CAN)
• international standards organization (ISO) 9141 communications network
• universal asynchronous receiver-transmitter (UART) based protocol (UBP) communications network

The diagnostic tool connects to the communications networks through the data link connector (DLC). The DLC allows a diagnostic tool access to diagnose and test the vehicle systems of any module on the communications networks.

The CAN has an unshielded twisted pair cable, data plus circuit 1908 (WH) and data minus circuit 1909 (BK). The CAN is a communications network used for the anti-lock brake system (ABS) module, the instrument cluster, powertrain control module (PCM) and the trailer brake controller communications. The CAN remains operational even with the severing of one of the CAN circuits but operates at a degraded level. Communications also continue at a degraded level if one of the CAN circuits are shorted to ground or voltage, or if some but not all termination resistors are lost.

The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must request all information or initiate module commands. The ISO 9141 communications network is a communications network used for the 4-wheel drive (4WD) control module, the parking aid module and the restraint control module (RCM) communications. The ISO 9141 communications network does not function if the circuit is shorted to ground or voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fail.

The UBP communications network is a single circuit communications network, circuit 693 (OG). The UBP communications network is a communications network used for the electronic automatic temperature control (EATC) module, the instrument cluster and the vehicle security module communications. The UBP communications network does not function if the circuit is shorted to ground or voltage. The UBP communications network is different from the ISO 9141 communications network in that it allows intermodule communication.