•  The vehicle has two module communications networks. The standard corporate protocol (SCP) network, which is an unshielded twisted pair cable (data bus plus, circuit 914 [TN/OG] and data bus minus, circuit 915 [PK/LB]); and the international standards organization (ISO) 9141 network which is a single wire (circuit 70 [LB/WH]). The diagnostic tool can connect to both networks through the data link connector-2 (DLC-2). This makes diagnosis and testing of these systems easier by allowing one smart tester to be able to diagnose and control any module on the two networks from one connector. The DLC-2 can be found under the dashboard on the driver side.

•  The SCP communication network will remain operational even with the severing of one of the bus wires. Communications will also continue if one of the bus wires is shorted to ground or power supply, or if some, but not all, termination resistors are lost.

•  The ISO 9141 communication network does not permit inter-module 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.

•  Unlike the SCP, the ISO 9141 communication network will not function if the wire is shorted to ground or power supply. Also, if one of the modules on the ISO 9141 communication network loses power or shorts internally, communications to that module will fail.

•  The PCM is connected to the SCP communication network. The PCM controls the engine for better fuel economy, emissions control, and malfunction mode detection and storage.

•  The immobilizer system is integrated into the PCM module. The PCM/immobilizer system is connected to the vehicle electrical system, the transceiver module, the vehicle SCP communications network and the security light located in the instrument cluster. The PCM module uses a microprocessor to control the system functions as well as illumination of the security light. The illumination command is sent from the PCM through the SCP communications network to the instrument cluster, which in turn sends power to the security light. The PCM module microprocessor stores the ignition key codes in non-volatile memory. The PCM and instrument cluster modules can be diagnosed through the DLC.

•  The SAS control module is connected to the ISO 9141 communication network. The SAS control module controls the deployment of the air bags based on sensor input.

•  The generic electronic module (GEM) is connected to the ISO 9141 communication network. The GEM controls a variety of systems

•  The anti-lock brake system (ABS) control module is connected to the ISO 9141 communication network. The ABS module controls the brake pressure to the four wheels to keep the vehicle under control while braking.