2000 Envoy no 4WD

I have a 2000 Envoy that will not shift out of 2WD. None of the lights work on the switch. The encoder motor was replaced last summer due to it's
failure. I just replaced the TCCM today, no change. It's showing a 4X4 DTC, but AutoTap does not read those. Does anyone know if Autozone can read them?
Thanks Dante
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