I'm a single dad ...bought my daughter a 08 is250 awd !did the 2is to 3is front end conversion cause that's what she wanted but my question is what would make the awd system stop working all together ? I been looking and reading post about the check awd light vsc brake lights etc and all those lights are on but I was going to pull it in the front yard to wash it and in wet grass it one wheel peeled meaning only 1 rear wheel was spinning and I was like wth? Jacked it up and put it on jack stands and put it in drive and front wheels weren't moving ! Other people I seen that said they were getting the check awd light said it would still work just the light was on hers not working ! Rear end just recently went out "I think" and while messing with it today I crank it up and put it in gear and trans works fine , drive shaft turning but no wheels moving and making terrible noise so guessing it's the rear end

 

As for the rear, these have an open diff (both ends) so if stuck you get one wheel at each end with the LEAST amount of traction spinning.

If you suspect the front diff or x'fer case, I'd start with fluid dump and fill and see what it looks like.