I would check the voltage on the buttons. Mine did the same thing and it turned out to be the buttons. Sometimes the button switch can do weird things.

So the electornics in the system work like this. The TCCM receives signals from the buttons, front axle sensor, ParkReverseDrive switch, Speed sensor, and a sensor on the encoder motor. Those are the only things that affect your what your buttons tell you is going on. Vac won't cause that problem.

 

Hi guys. I have the same problem on my 1992 blazer.
Where do I have to take a look(?!)
Is there a way to put manual locking hubs and manual actuator for the front drive?
thanks a lot

 

If you have the NP233 electric shift transfer case, search for "NV233" and see what comes up. This thread is about the NV236 which was not available in the 1st gens.

About manual locking hubs, no dice. There is no way to use manual locking hubs given the way the s-series hubs are configured. You would have to do a LOT of redesigning of the hubs, etc to get disconnects at the wheels like the solid axle folks have.