4x4 actuator on the front differential cycles back and forth on 2002 GMC Sierra 1500

02 GMC Sierra, 5.3
The dash button for 4x4 shows blinking in the 4x4 hi position. When I press the 2 wd button, the actuator arm on the front diff. retracts, extends, retracts and then extends again where it then stays causing the front end to be and stay engaged. (I took the actuator off and plugged it back in to watch it do this) Had my daughter hit the button so I could unplug it when the are retracted so I can at least drive to work on dry roads in 2 wd. With the snow we've had recently, really need to get this figured out and fixed.
I replaced the switch assembly on the dash with no improvement. 4 wd high light blinks and the dash warning says service 4 wd. Any help as to what would cause the actuator motor to extend and retract repeatedly?

Thanks in advance for any help.

Asked by for the 2002 GMC Sierra 1500
ALL OF THE 4X4 functions are controlled by the transfer case module. To find the fault for this it needs to be scanned, preferably by a Tech2 scanner. It can read all the functions of the transfer case.
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