WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View of Rear Door Sill Plate Assembly
Courtesy of GENERAL MOTORS CORP.
Callout
Component Name
1
Rear Side Door Sill Plate Procedure: Pull up at the rear edge first, then pull rearward to remove.