2002 Ford Explorer 4X4 selection control

Sounds like a shift motor issue. Fords seem to be famous.I had the same problem with mine (although it is a 1993) Anyway. When you push the button can you hear a "clicking" sound coming from the rear end? Anyway here is a great link. Some good reading, and it worked for me. I never got as far as taking the motor apart.I just had to "tap" the shift motor with a rubber mallot, and low and behold, it worked. Must have knocked some of the carbon build up lose. Give it a shot