Initial Inspection and Diagnostic Overview

Data Link References

This table identifies which serial data link that a particular module uses for in-vehicle data transmission. Some modules may use more than one data link to communicate. Some modules may have multiple communication circuits passing through them without actively communicating on that data link. This table is used to assist in correcting a communication malfunction. The body control module (BCM) emulates some devices that are on high speed GMLAN serial data circuit to the modules on class 2 serial data circuit. The BCM transmits multiple Node Alive messages using source IDs that correspond to each of those high speed GMLAN nodes. This is in addition to the BCM behaving itself as a real node. For the description and operation of these serial data communication circuits refer to Data Link Communications Description and Operation (Description and Operation).

Important: If the scan tool does not communicate with the vehicle the class two serial data bus must be diagnosed, repaired and functional first in order to prevent misdiagnosis.