99 Blazer LS 4X4 Problem

I have the 4x4 auto trac system (4 button switch on dash). My problem is that it will not shift from 4lo to 2 hi or to 4 hi at all. I can hear the transfer case control module clicking. It does this clicking every time i turn the key to start truck is this normal? ive only had truck for 2 weeks now. I have unplugged module and then plugged back in and it will go into 2 hi, but the service 4wd lite is on now. Any clue as to whats happening???

I experienced the very same problem on my 95, clicking and all. When I opened the upper (check level) plug, 2 quarts of ATF came pouring out. Once the Tcase wasn't WAY overfilled it started shifting just fine. I haven't had time to check why it was overfilled (one suggestion was a leaky gasket between the tranny and Tcase) due to lack of time.

If you haven't already, make sure the fuse isn't burnt. If you replace it and it burns out again I can almost guarantee that overfilling is your problem.

Other suggestions before I found this as the problem were grungy fluid and the actuator motor. If you're hearing it click then it isn't your switch.

Remember that these Tcases take dextron 3, and not gear lubricant. My parts guy tried selling me 80/90 when I told him I was going to change my Tcase fluids... I almost had to lay the smack down!

Edit: You may also want to check the vacuum lines running to the actuator motor.