WARNING: This page is about a different car, the 2002 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Vehicle Communication Unit (VCU) Connector End View
Courtesy of GENERAL MOTORS CORP.
Fig 2: Vehicle Interface Unit (VIU) C1 Connector End View
Courtesy of GENERAL MOTORS CORP.
Fig 3: Vehicle Interface Unit (VIU) C2 Connector End View