Principles of Operation

PRINCIPLES OF OPERATION

The module communications network consists of the following:
- data link connector (DLC) C251
- powertrain control module (PCM)
- instrument cluster
- restraint control module (RCM)
- anti-lock brake system (ABS) module
- ABS module with roll stability control (RSC) (if equipped)
- vehicle security module (if equipped)

The vehicle has 2 module communications network protocols:
- controller area network (CAN)
- international standards organization (ISO) 9141 communications network

Controller Area Network (CAN)
The CAN is an unshielded twisted pair cable, data plus circuit 1827 (WH/LG) and data minus circuit 1828 (PK/LG). The CAN can be awake when the key is in the OFF position to carry out functions such as delay accessory. In order to do diagnostics, it is necessary to have the key in the ON position. On the CAN, there are 2 terminating modules composed of the powertrain control module (PCM) and the instrument cluster, which are located at the far opposite ends of the CAN wiring. The 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.

International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). The ISO 9141 communications network does not permit inter-module communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must ask for all information; the modules cannot initiate communications. The ISO 9141 communications network does not function if the circuit is shorted to ground or voltage, or there is an open. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module will fail. The ISO 9141 communications network is used to communicate with the RCM.