Could this stop my unit from going into 4X4? I guess it is on the transfer case. Is it changeable or should I get it done by the shop.

 

You can unplug the CAD vacuum lines there should be vacuum on one in 2wd and vacuum on the other in 4wd. If that works as i said you could have a stuck, or defective vacuum motor or internal problems. If there is no vacuum at either one i would unplug the vacuum harness from the vacuum switch on the transfer case and test for vacuum at one port. If you have vacuum you could then test the two lines going to the CAD. If they check ok replace the vacuum switch. If there is no vacuum to the switch you will have to trace the harness to a tee in the vacuum pump harness and find out where its broken.