You can search threads on this forum about your transfer case electric motor.
This happened to mine.... the electric motor has three settings, 4hi, 4lo, and hi. The motor turns to each position, as selected.
Problem: the small internal bushings on the selector wear out and disintegrate. Then the selector, especially for 4lo, goes off the track, too far, and is “lost” by the controller. Lost and stuck in 4 lo.
Solution is to remove transfer case motor, and replace bushings. You can use very small round pieces of vacuum hose, I think.
Then all be well again. Just a possibility. Good luck.