1998awdastro

Which i think is odd, wife came home last night was dark it was fine, seeings how she took up half the driveway i decided to let hers warm up and use it then park it where it needs to be, well 4wd service light came on and is stuck in 4low........
I deconnected the negative battery lead for 5 minutes plugged it back in started the truck went to netr. then hit the auto 4wd and it switched heard it switch too......im thinking something is alittle frozen, maybe some moisture got up in there?
well i got it switched over for her she went to work and when she got there and put it in park it switched back to 4low..
she did say however that after a mile form the house the light came back on (service 4wd).
A friends Father inalws 1996 S10 2dr blazer had the same problem and he fixed his but somthing that was called a timmer behind headlight switched? is it possible i am having the same issues? it did switch back to 4auto after resetting puter.........
any ideas! thanks for any help....