Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 3 module communication networks:
- international standards organization (ISO) 9141
- medium speed controller area network (CAN)
- high speed CAN

All 3 networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing 1 diagnostic tool to be able to diagnose and control any module on the 3 networks from 1 connector. The DLC can be found under the instrument panel between the steering column and the audio unit.

ISO 9141 Communications Network
The ISO 9141 communications network is a single wire 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 communication network, the diagnostic tool must ask for all information; the modules cannot initiate communications. The ISO 9141 communications network does not function if the wire is shorted to ground or battery voltage. Also, if one of the modules on the ISO 9141 communications network loses voltage or shorts internally, communications to that module fail. The restraint control module is the only module on this ISO 9141 communication network.

Medium Speed CAN
The medium speed CAN has an unshielded twisted pair cable, data plus circuit 1827 (WH/LG) and data bus minus, circuit 1828 (PK/LG). The medium speed CAN is used for smart junction box (SJB) and electronic automatic temperature control (EATC) module communications. The medium speed CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If CAN data minus is shorted to ground or an open exists on either bus line, module-to-module and module-to-tester communication is marginal at best. The CAN bus may remain operational when one of the two termination resistors are not present.

High Speed CAN
The high speed CAN also has an unshielded twisted pair cable, data bus plus circuit 1847 (WH/OG) and data bus minus, circuit 1848 (PK/OG). The high speed CAN is a high speed communication network used for instrument cluster, powertrain control module (PCM) and anti-lock brake system (ABS) module communication. The high speed CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If CAN data minus is shorted to ground or an open exists on either bus line, module-to-module and module-to-tester communication is marginal at best. The CAN bus may remain operational when one of the two termination resistors are not present.