WARNING: This page is about a different car, the 1995 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
PCM turns on MIL. PCM disables cruise control.
Fig 1: Code P091 Schematic, Transaxle Range Switch Problem
Courtesy of GENERAL MOTORS CORP.
Fig 2: Code P091 Diagnostic Flow Chart, Transaxle Range Switch Problem