transfer case control module

How do you know if the transfer case control module is bad. I have a 96 gmc jimmy 4x4 i can't shift into 4 wheel drive only four low

I don't know about the 96, but my on my 2000 the TCM is located on passenger side, right behing the right kick plate. Pull off plastic cover, 4 bolts and 2 wiring connectors. Mine had rust on the exterior by the connectors meaning water getting in.

Let me know.