Code P063, Vehicle Speed & Set Speed Difference Too High: Notes
WARNING: This page is about a different car, the 1995 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
Code P063 will set and disengage cruise control if vehicle speed is 20 MPH greater than cruise set speed. Code P063 is designed to detect a cruise control problem that results in cruise overspeed or inability to hold speed.