4x4 hi sticked engegment

[sllerena]

My silverado's 2005, 2500 transfer is stickied in 4x4 hi, if the buttons to change to 2hi, auto or 4x4 low are pushed, you can hear different tones of sound training to change gear in the transfer but it doesn't change. After insisting particularly to engage 4x4 Low it does, and then can change to 2 Hi. I suppose the problem is in the transfer. Will you have a suggestion for this?. tanks.

[chevroletmb]

have it scanned for codes , could be encoder motor