WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Heated Seat Temperature Adjustment Inoperative Symptom Diagnostic Procedure Chart (1 Of 2)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Heated Seat Temperature Adjustment Inoperative Symptom Diagnostic Procedure Chart (2 Of 2)