4 wheel drive not engaging - recent transfer case swap- now grinding in reverse OK, now that the first snow of the year has flown I realized that the 4WD is not working on my 1999 Suburban 1/2 ton (NP 246 transfer case with pushbutton auto 4WD). Here are the facts: Swapped out the transfer case this fall with a factory new rebuilt unit that I bought from someone on Craigslist. It looked like it had never been installed and the transfer case doesn't make any unusual noise. When I select Auto 4WD, 4 Hi, 4 Lo the indicator light shows that it is engaged and I can hear the shift motor operating. However the rear wheels will spin and the front's are not engaged. (i.e. I can drive around in 4WD, it just doesn't engage the front wheels) There is no funny noise coming from the transfer case. I haven't crawled under to look at anything, but I'm curious if anyone has any suggestions of what I should look for. Will there be codes I can have pulled from the auto parts store? The check engine light is not on. Any feedback would be helpful. Thanks!