WARNING: This page is about a different car, the 2005 Pontiac Pursuit and 2005 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: DLC Power, Ground, and Low Speed GMLAN Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 2: DLC High Speed, Serial Data, and Class 2 Schematic