I just got mine back from the dealership for the same issue. Try this link below. You can access the ground by popping off the a-pillar cover. See if the plastic piece is under the nut on the ground terminal. Mine was. They also replaced both battery cables and the terminal block. I've had it back for a week now and so far it seems to be fixed.
http://gm.oemdtc.com/3194/reduced-power-steering-assist-engine-stall-ipc-radio-hvac-goes-blank-various-dtcs-2014-2016-cadillac-chevrolet-gmc