It could be anything from a bad switch to a transfer case but the common problems are a vacuum leak or an encoder motor on the transfer case. It may also be the 4 wheel drive module. Check in the correct section on the forum for 4 wheel drive diagnostics and good luck. Let us know what you find.

 

I vote for finding a really muddy area and drive it in. If you get stuck and only 2 wheels are spinning then well u found your answer.

 

ok thanks ill figure it out and post what it was