2004 Navigator stuck in 4wd Low although 2H is selected. Air suspension continuously raising

Most often this is a bad shift motor. Fords are known for this. The shift motor is mounted on the transfer case. It's a pretty easy replacement--usually only 4 bolts. The only bug is that the motor is internally grounded inside the transfer case. So when you install the new motor, you'll have to either move the existing ground wire to the new electrical connector or solder it into the new ground. You can get aftermarket motors for about $125. Relatively easy fix. Something you can do yourself with a shop manual and ordinary metric sockets.

This not my information I found it on another forum, hope it helps