WARNING: This page is about a different car, the 2003 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: DTC P2100: Throttle Control System - Excessive Pulse Width Modulation Detected (Steps 1 & 2)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC P2100: Throttle Control System - Excessive Pulse Width Modulation Detected (Steps 3-14)