Are you sure that the font end is not locking in? Did you try putting it in 4H, and then spin the tires in the mud or snow? Do the front tires spin? Might be able to put the front actuator on a toggle switch. If you try that, make sure you use a circuit that only has power when the ignition is on. Also, only hit the switch under the correct circumstances, what ever those might be. You may be able to call the dealership parts department and explain that the sensor is bad, and ask them to look it up on their exploded view parts diagram.
Supreme Pizza's post in 4Lo works, 4hi doesn't, help please was marked as the answer