Visual/Physical Inspection
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, and 2002 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
Inspect for aftermarket devices which could affect the operation of the automatic transmission shift lock control system. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.