My 2000 Blazer had 4WD service light come on this week. It was stuck in 4 wheel auto and would blink the Lo light when you pushed 2WD but it stay in auto mode. I checked vacuum lines were good since many suggested they were a possible issue. I got the Tech2 out and it came back with code B2725 - Automatic transfer case mode switch malfunction. I wasn't sure if this was the switch on the dash or on the transfer case? Then I read a article in the Avalanche forum Google threw at me when I searched code B2725
http://www.chevyavalanchefanclub.com...tml#msg1757910
I did same as RSmike, took the switch out of the dash. Popped apart and re-soldered all the connections. Everything is good again and shifting with no error message on dash. If you were not able to solder orthe switch had issues I saw Dorman sold a new switch for $17, Part #901-060. Kevin