I have a 95 blazer. On a trip to the doctors, my 4 wheel drive worked fine. On my way home, the buttons didn't light up and nothing would engage. When I got home, I found it would go into 4lo but not 4hi. the 2 4 wheel drive buttons would just blink back and forth. When I tried to put it in 4hi, the motor made a short, whining sound. I then disconnected the battery for a minute and tried again. It went into 4hi about twice ok, but started the problem again

 

Check out the OBD2 Non-Automatic Transfer Case Diagnostics thread in the Tech Article (DIY) section to read the codes from the TCCM. This behavior is indicative of an encoder motor fault.