We recently had a service 4wd light that did not stay on on our 2001 Blazer.
Today it was stuck in 4wd low when the wife tried to go to lunch. I was able to play around and get it to shift back to 2wd hi after several attempts.

Tonight after reading on here about such problems I went out and found the TCCM and unplugged the connections. The terminals all looked good but there are some signs that water had been getting on the top plug (one with 4 wires)

Everything I read here talked about checking for corrosion at the plugs but no one talked about were the water is getting in at.

At this point I have the TCCM disconnected hoping to keep it in 2wd hi till I can find the time to properly troubleshoot the system. From what I have been reading it may be the encoder motor but time will tell.

Blazeme

 

could be the passenger side door hinge bushings broken. This allows the door to sag and not seal properly allowing water in.

 

For mine it was just snow and rain (mostly snow) trampled in on your feet. The carpet gets wet and since the plugs face down into the carpet it doesn't take much for the moisture to get in.

 

This may be what I have going on right here. There is some play in the door bushings on the front of our Blazer. Not much water has got in so far but guess I will have to get them changed.

Thanks for the help.

Blazeme