Ok so i got in my 2000 blazer 4x4 with the 4 button switch this morning to go to work and i noticed that the truck was in 4hi right after i started it.. weird.. so i was driving to work (3 mile trip) and the TCCM (i'm assuming) in the passenger dashboard started "clicking" at the same time my check 4x4 light came on with all of my 2hi, 4hi, 4lo, n, and auto 4x4 all came on while the clicking was going on. It never tried to shift out of 2hi or anything drove fine. I need help figuring out what is going on since this is my daily driver and i don't have a back up! Thanks for all your help!

 

As with every thread concerning 4wd problems, start by checking the connections at the switch, TCCM, and encoder motor for corrosion.