99 GMC Jimmy 4x4 problem

Ok, I have a problem with my truck, the Transfer case control module keeps dying on me I've replaced it once with a salvage yard one, for some reason
it will work about two weeks than it just goes out again. when it goes out, I have no lights on the dash and I dont hear it click when I turn on the ignition switch. I talked to someone they told me my encoder motor could be bad, how could I tell that?? When the 4x4 did work it shifted fine in and out of all ranges. I have the NP8 transfer case.
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