WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Power, Ground, and Low Speed GMLAN Serial Data Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 2: GMLAN - High Speed Serial Data Wake Up Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 3: GMLAN High Speed Serial Data (North America) Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 4: GMLAN High Speed Serial Data (North America) Schematic