99 blazer 4x4 problems

I have a 1999 chevrolet blazer 4x4 with awd. everytime i try to go into 4hi it jumps to 4 low. it will not even go into 4 hi. i have replaced the encoder motor and am still having this problem can anybody please help

Which transfer case?
Does the shift buttons have the auto mode button?

it is the four button switch.

it is the four button switch.

Does one of the say auto on it?
The transfer case ID can be found on the back of it.
Is it a 233 or a 236?

DO THE BUTTONS LIGHT UP FOR A BULB CHECK KEY ON AND THE GO OFF?
Or does any stay on or blink at you?
Any check engine lights or other lights on?
We need to know which one you have before we can help.
MT

it does say auto on the buttons ... also it is a 236 transfer case.... and the lights do blink when key is turned on and then do go off. the transfer case will go into 4wd low on its own and is hare to get back into 4wd high or 2wd

OK 236 it is.

The 236 is a computer controlled transfer case and you will need a transfer case/transmissionn /engine capable scanner to test and check out and get codes.
Get the code/codes and post back code no.
MT