WARNING: This page is about a different car, the 2008 Saturn Outlook, 2008 GMC Acadia, and 2008 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Low Speed GMLAN
Courtesy of GENERAL MOTORS CORP.
Fig 2: High Speed GMLAN
Courtesy of GENERAL MOTORS CORP.
Fig 3: Communication Enable and Local Interconnect Network (LIN)