I have a 03 3500 4x4. My indicator light shows the ATC to be locked in 4low but it is really not. Even though the drive shaft is locked. This seems to only happen when I crank the truck but it does not do this all the time. Some times I can just press the 2 wheel drive button and it goes back or then other times I have to mess with it several time to get it back to 2 wheel drive. At that point the drive shaft is free to turn by hand. Any ideas. I also have access to a Tech II if someone can tell me how to use it to trouble shoot this problem. Thanks for the help.

 

Most likely the motor on the tcase is going out. Just had one in the shop last week with the same issues and that's what solved it. Also check the grounds right by the motor that connect to the frame on the drivers side iirc and that can case issues as well. Also is it setting the "service 4x4" in the gauge cluster?

 

Find anything out?