If you have a customer that is reporting their GM Delphi does not function along with their rear entertainment system, first just verify that they have the actual "DVD" logo on the front of it.
If they DO NOT, then they will need to exchange the radio for one that does or has simply been programmed for functionality with the rear entertainment.
If they do have the DVD logo and the unit is still not functioning with their rear entertainment system, more than likely the unit has not been programmed for the rear entertainment capabilities and will need to be brought in for a programming service.