Some new vehicles have components that are in a service loop. Meaning, the main computer is connected to a tranny computer, tranny connected to the main radio, main radio connected to airbag system and so on.
By taking out the HU (main radio) you broke the chain of information getting back to the diagnostic port and the reader will not work.

Its a simple fix if the stereo installers didnt hack your wire harness.
Pull the kenwood out and plug in your factory OEM HU.
Then take the X to get the diagnostic done.
When your done pop in the kenwood.