Diagnostic Communications Network

The diagnostic communication network consists of a single wire circuit which allows communication between an off board tester and the related modules.

Fault Tolerance
Unlike the multiplex communications network, the diagnostic communications network will not tolerate grounding of Circuit 70 (LB/W). The diagnostic communications network will also fail if Circuit 70 (LB/W) is shorted to B+. Also, if one of the modules on the diagnostic communications network loses power or shorts internally, communications to that module will fail.

Purpose
This network consists of a single wire, Circuit 70 (LB/W). 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 New Generation Star 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 New Generation Star Tester unless the tester requests information by sending the module a signal.

The diagnostic communication network, Circuit 70 (LB/W), is located on Pin 7 of the data link connector (DLC). The voltage at Pin 7, Circuit 70 (LB/W), during vehicle operation without the New Generation Star Tester connected to the DLC will float between ground and battery voltage. When the New Generation Star Tester is connected to the DLC, the voltage on Pin 7, Circuit 70 (LB /W), should be greater than 90% of battery voltage.

To begin communications with selected vehicle module, the New Generation Star Tester grounds Pin 7, Circuit 70 (LB/W). The New Generation Star Tester then sends signals to the module by switching Circuit 70 (LB/W) between battery voltage and ground. The selected module interprets these digital commands and performs the requested function.

Module Identification
Modules on this diagnostic network are:

- Anti-Lock Brake System (ABS) Module

NOTE: The Anti-lock Brake System (ABS) module is included on this network only if the vehicle is not equipped with traction control.

The Anti-lock Brake System (ABS) module is located under the battery tray in the lower LH side of the engine compartment. The ABS module provides diagnostic services via the module communications network on Circuit 70 (LB/W). A failure of the ABS module or on Circuit 70 (LB/W) may cause the New Generation Star Tester to indicate a communication error. In the event the New Generation Star Tester fails to communicate with the ABS module, refer to Anti-Lock Brake System for No Communication Diagnostics.

- Generic Electronic Module (GEM)
The Generic Electronic Module (GEM) is connected directly to the fuse junction panel located in the passenger compartment on the driver side to the left of the steering column. The GEM provides diagnostic service via Circuit 70 (LB/W). A failure of the GEM or Circuit 70 (LB/W) may cause the New Generation Star Tester to indicate a communication error. In the event the New Generation Star Tester fails to communicate to the GEM, refer to the appropriate sub-system of the system being tested for No Communication Diagnostics.

- Integrated Air Bag Monitor (IABM)
The integrated air bag monitor is located behind the instrument panel to the right of the steering column as far up as can be located. The IABM provides diagnostic service to the New Generation Star Tester through Circuit 70 (LB/W). In the event the New Generation Star Tester fails to communicate with the IABM, refer to Air Bag and Seat Belts for No Communication Diagnostics.