[wolfox]

Make and model will help us narrow down your problems, but i will take a stab in the dark at the more common issues -

There are two major parts that make up the pushbutton 4WD on demand system that are your most likely culprits. One is the TCC or Transfer Case Controller located inside the cab of the truck. THis module can suffer from logic lock or just get plain weak over the years to where it will not drive the Transfer Case Actuator motor properly. The latter, is located on the body of the Transfer case under the vehicle and this is what slips the truck into various 4x4 modes and 2x4 high range.

If you remove the negative battery terminal for 20 minutes and then reconnect it - and this as a result makes the problem go away - I am inclined to think it's the control module inside the truck's cab. If it continues, indicating a fault - then I would suspect the drive motor module on top of the transfer case.

If you have a '97 and later vehicle, such as a Bravada or GMC Jimmy with this trouble with automatic AWD/4x4 system, you may have to have the transfer case serviced with the proper GM AllTrack-II fluid. (It will be blue in color) This fluid like others can just wear out with age and time, creating all sorts of strange behaviors on and off pavement and in loose terrain or slick conditions.

Good luck and let us know what year/make/model you're needing help with and we'll try to help more.