Try disconnecting the battery. Let it sit for a few minutes and reconnect. This will reset your computer.
that is in the push button switch.replace it That is not always true. I have already done that and it still randomly put my 2003 Chevy Silverado in 4WDl or 4WDH, I also have put a new transfer case on. To this day it still isn't fixed. My next step is replacing the encoder sensor.
i have a 1988 sliverado 350 5 speed 4x4 1500 single cab short wheel base with automatic hubs and the front wheels wont pull and no popping or grinding noise at all and the transfer case will let you put in all 4wdL 4wdH N 2wd put the wheels wont pull and the light doesn't come on