4wd Not Working Below Freezing

My 4 WD will not work below freezing. When the button is pushed, I hear something click underneath the front, which sounds like it is going into 4WD. But it is not working. This happened last winter also but went away after a few weeks. While driving below freezing it also at times tries to go into 4WD by itself. I hear a loud, grinding, whining noise. But it won't engage until I press the button. That was the problem last winter now it won't work at all below freezing.

Sounds like either your vacuum switch on top of the transfer case is sticking or the acutator cable on the front diff is binding and not engaging or disengaging properly. Either way, if you have had grinding occur, the gear inside the front diff has been damaged and will likely need to be replaced. Have the front diff fluid drained and check the fluid for filings. If you find metal, you know it needs to come apart. I had the same problem in extreme cold temperatures at highway speeds. I ended up replacing the vacuum switch first, the problem occurred again and the diff started grinding, so I had that overhauled and replaced the cable for safe measure. Problem has not occured for the past 60 days since I had it done.