Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 3 module communication networks:
- high speed controller area network (CAN)
- medium speed CAN
- International Standards Organization (ISO) 9141 communications network

The diagnostic tool connects to the communication 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 communication networks.

All 3 communication networks are connected to the 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 communication networks from 1 common connector. The DLC can be found under the instrument panel between the steering column and the driver door.

High Speed Controller Area Network (CAN)
The high speed CAN is an unshielded twisted pair cable, data plus circuit 1827 (WH/LG) and data minus circuit 1828 (PK/LG).

The high speed CAN is a high speed communication network used for the anti-lock brake system (ABS) module, the instrument cluster and the powertrain control module (PCM) communication. The ABS module, the PCM and the instrument cluster use the high speed CAN to communicate information back and forth such as engine RPM, vehicle speed and odometer. The modules on the high speed CAN are ignition switched. The high speed CAN is only on when the key is in the ON position.

The high speed CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or the high speed CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If the high speed 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 high speed CAN bus may remain operational when 1 of the 2 termination resistors are not present. If there are issues with the high speed CAN, there may be missing functionality and problems connecting with a diagnostic tool. On the CAN, there are 2 terminating modules which are composed of the PCM and the instrument cluster which are located at the far opposite ends of the CAN wiring.

Medium Speed Controller Area Network (CAN)
The medium speed CAN is an unshielded twisted pair cable, data plus circuit 1847 (WH/OG) and data minus circuit 1848 (PK/OG).

The medium speed CAN is a medium speed communication network used for the audio unit, the instrument cluster, and the smart junction box (SJB) communication. The SJB, the instrument cluster and the audio unit use the medium speed CAN to communicate information back and forth such as dimming, fuel level, turn signal indicator on the instrument cluster and vehicle compensated volume. The medium speed CAN can be awake when the key is in the OFF position to carry out functions such as delay accessory. In order to carry out diagnostics, it is necessary to have the key in the ON position.

The medium speed CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or the medium speed CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If the medium speed 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 medium speed CAN bus may remain operational when 1 of the 2 termination resistors are not present. If there are issues with the medium speed CAN, there may be missing functionality and problems connecting with a diagnostic tool. On the CAN, there are 2 terminating modules which are composed of the SJB and the instrument cluster which are located at the far opposite ends of the CAN wiring.

International Standards Organization (ISO) 9141 Communication Network
The ISO 9141 communication network is a single circuit communication network, circuit 70 (LB/WH). The ISO 9141 communication 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 communication. The ISO 9141 communication network does not function if the circuit is shorted to ground, shorted to voltage or is open. Also, if one of the modules on the ISO 9141 communication network loses power or shorts internally, communication to that module fails. The ISO 9141 communication network is used to communicate with the restraint control module (RCM).