Diagnostic Starting Point - Data Link Communications

Begin the diagnosis of the data link communications by performing the Diagnostic System Check for the system in which the customer concern is apparent. The Diagnostic System Check will direct you to the correct procedure within the Data Link Communications section when a communication malfunction is present.

Establish serial data communications with each controller. Read and record the DTCs from each controller. It is important to systematically approach serial data communications diagnostics. This vehicle has 2 separate data links with 3 different circuits to communicate to the various data links.

The high speed CAN link which supports real-time information between the ECM, TCM, EBCM, and BCM is accessible through 2 different keyword circuits.

1. Circuit 2960 supports communication (Keyword 2000) from the DLC to the ECM and TCM.
2. Circuit 2960 supports communication (Keyword 2000) from the DLC to the EBCM.

CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM. The ECM, TCM, EBCM, and BCM all communicate on the CAN serial data line.

The other modules communicate on the Class II link which is configured in a ring, except for the OnStar® module. The ring configuration provides redundant communication paths, so that a single open does not prevent a serial communications malfunction.