The Module Communication Network Components, Part 1
Part 2
The vehicle has two module communication networks:
the Standard Corporate Protocol (SCP) which is an unshielded twisted pair cable (data bus plus, circuit 131 [W/BL] and data bus minus, circuit 132 [BK/BL]), and the International Standards Organization (ISO) 9141 network which is a single wire (circuit 529 [O/BL]). Both networks can be connected to the scan tool at one connector called the Data Link Connector(DLC) . This makes troubleshooting 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 can be found under the instrument panel between the steering column and the radio.
The ISO 9141 communication network does not permit inter-module communication. When the scan tool communicates to modules on the diagnostic communication network, the scan tool must ask for all information; the modules cannot initiate communications.
The SCP 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 chassis ground or battery positive voltage (B+) or if a termination resistor is lost. This faulted condition is detected and reported to the host by the module's network bus interface circuits.
Unlike the SCP network, the ISO 9141 network will not function if the wire is shorted to chassis ground or battery positive voltage (B+). Also, if one of the modules on the ISO 9141 network loses power or shorts internally, communication to that module will fail and communication to all modules on the ISO 9141 network may fail. There is one module on the SCP network and three optional modules on the ISO 9141 network.
The Powertrain Control Module (PCM) is on the SCP communication network. The PCM controls the engine for better fuel economy, emissions control, and failure mode detection and storage. Refer to Symptom Chart for diagnosis and testing of the PCM. See: Testing and Inspection\Symptom Related Diagnostic Procedures
The Electronic Crash Sensor (ECS) module is a optional module on the ISO 9141 network. The ECS controls the deployment of the air bags based on sensor input; refer to Air Bag Systems.
The Remote Anti-Theft Personality (RAP) module is an optional module on the ISO 9141 network. The RAP module controls the remote entry, trunk release and panic alarm from the remote entry transmitter; refer to Keyless Entry and Antitheft and Alarm Systems.
The anti-lock brake control module is a optional module on the ISO 9141 network. The module controls the brake pressure to the four wheels to keep the vehicle under control while braking; refer to Antilock Brake System.
