Scan Tool Does Not Communicate with High Speed GMLAN Device: Notes
WARNING: This page is about a different car, the 2005 Pontiac Aztek and 2005 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules.