Description & Operation
Module communications network provides the ability for module-to-module communication by sharing inputs and outputs instead of each component having an input and output wired directly to each module. Vehicle has two module communications networks. First communications network is Standard Corporate Protocol (SCP) that is also referred to as data bus positive (circuit No. 914) and data bus negative (circuit No. 915), which consists of a pair of unshielded twisted wires. Second communications network is International Standards Organization (ISO) 9141, which consists of a single wire (circuit No. 70).
Worldwide Diagnostic System (WDS) tester, New Generation Star (NGS) tester or equivalent diagnostic tool can connect to both networks through the Data Link Connector (DLC). DLC is located under instrument panel between steering column and radio. See Fig 1. 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. ISO 9141 communication network does not permit inter-module communication. When diagnostic tool communicates to modules on ISO 9141 communication network, diagnostic tool must ask for all the information, modules cannot initiate communications. 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 ground or battery positive voltage (B+) or if some, but not all, termination resistors are lost. Unlike SCP communication network, ISO 9141 communication network will not function if the wire is shorted to chassis ground or battery positive voltage (B+). Also, if one of the modules on ISO 9141 network loses power or shorts internally, communications to that module will fail. Powertrain Control Module (PCM) is on SCP communication network. PCM controls engine for better fuel economy, emissions control, and failure mode detection and storage. Restraint Control Module (RCM) is on ISO 9141 network. RCM controls deployment of the air bags based on sensor input. Generic Electronic Module (GEM) is on ISO 9141 network. GEM module controls a variety of systems including one touch down windows, wipers, perimeter anti-theft, and warning chimes. Anti-Lock Brake System (ABS) control module communicates over ISO 9141 communication network when not equipped with traction control and communicates over SCP communication network when it is equipped with the traction control option. ABS control module controls brake pressure to the four wheels to keep vehicle under control while braking. Remote Climate Control (RCC) module is on the SCP communication network. The RCC module controls the temperature within the vehicle. For module locations. See Fig 2. See COMPONENTS LOCATION table.