I have a 2001 tahoe with around 160,000 miles that the 4wd isn't working on. I have done numerous searches and just can't find what I'm looking for. Hoping someone here has some suggestions. Light comes on when I put it auto, lo, or hi. It also makes a clunk sound like it's engaging but front tires just sit and rear just spins. We are getting ready to go into winter so would like to get it working. If anyone has a troubleshooting guide or somewhere to start that would be great. Thanks for any help you can offer.