2005 Cadillac CTS navigation system

I recently put a factory navigation system in at a cadilac dealer and they can't get the system to operate properly. They say that since the car didn't come with it that's why it doesn't work. I don't believe that to be the case. The unit all seems to fuction well, just that it is not picking up the location of the car and the map and car doesn't move on the screen. The antenna is placed in the dash where it is suppose to be and every other feature works. Is there any kind of programing or other device that may be missing to make it work.

*note This car did not come with the unit from the factory. It was installed afterwards.

Any help would be greatly appreciated.

email fhouswerth1225@comcast. Net