WARNING: This page is about a different car, the 2005 GMC Sierra and 2005 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Module Power, Ground, Serial Data & MIL Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 2: Engine Data Sensors Schematic (5-Volt & Low References)