WARNING: This page is about a different car, the 2009 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
Courtesy of GENERAL MOTORS CORP.
Fig 2: GMLAN - High Speed Serial Data Wake Up
Courtesy of GENERAL MOTORS CORP.
Fig 3: GMLAN High Speed Serial Data (LH2 with LHD)
Courtesy of GENERAL MOTORS CORP.
Fig 4: GMLAN High Speed Serial Data (LC3 or LLT or LH2 with RHD)