Diagnostic Communications Network: Purpose
This network consists of a single wire, the Light Blue/White wire. This circuit is used to access certain subsystem modules to perform on-board diagnostics with an off-board tester. The recommended tester is the Rotunda New Generation Star (NGS) Tester (007-00500) or equivalent. The tester accesses the control modules via the Data Link Connector (DLC) located to the right of the steering column beneath the instrument panel. Information on this network is contained in messages. Each module on the network has the ability to send and receive messages to and from the NGS Tester.
Module-to-module communication is not possible as with the multiplex communication network. Communication involves only the New Generation Star Tester and the individual module being addressed during the testing of the module and its system. The modules will not communicate with the NGS Tester unless the tester requests information by sending the module a signal.
The diagnostic communication network, the Light Blue/White wire is located on terminal No. 7 of the DLC. See Fig 1 . The voltage at terminal No. 7 (Light Blue/White wire) during vehicle operation without the New Generation Star Tester connected to the DLC will float between ground and battery voltage. When the NGS Tester is connected to the DLC, the voltage on terminal No. 7 should be greater than 90% of battery voltage.
To begin communications with selected vehicle module, the NGS Tester grounds terminal No. 7. The NGS Tester then sends signals to the module by switching the Light Blue/White wire between battery voltage and ground. The selected module interprets these digital commands and performs the requested function.