I have similar issue BUT mine works fine on a cold engine (for about 10 minutes after starting in the morning) however, once engine runs for a bit it won't engage from 2WD - 4H. Any thoughts on why it works on 'cold' engine but will not after it has been running for a bit?

 

Mine is doing the same thing any thoughts

 

Look at all the things described above, it's typically
1. One of the VSVs is bad (gummed up or diaphragm has a hole)
2. No vacuum to the VSVs
3. Bad motor in the t-case
4. Bad status switch in the t-case or VSV assy.

 

I went to the junk yard and picked up 3 sets of VSV tested one it was good put it on and now 4wd is working properly when cold and hot thank goodness it wasn’t something major