07 classic np246 rarely able to switch

[2007gmc1500]

hey guys, winters here and i found a problem with my 07 sierra, when i press the switch to go into 4wd or auto nothing happens the selector switch stays solid on 2wd,  itdoesnt flash or anything when i try selecting 4wd. i replaced the selector switch with a known good one off another truck but same thing i now have service 4wd constant. after playing with it and pulling all the fuses to check them it started to switch perfectly but as soon as i went on a drive it once again service 4wd and will not switch except somtimes if i start pulling the fuses and putting them back 

[richard wysong]

any codes? is the transfer case engaging but not the  hubs?

[Supreme Pizza]

I would guess that the encoder motor is bad. They have a bunch of electrical connections inside of them that can go bad.

 

The round black ring have multiple electrical probes that slide on a disk.

 

As the disk turns, it redirects power though the different probes, and that tells the computer what position the encoder motor is in.