I believe what you are refering to on the radio NAV button is just a connection to an external Garmin/HD ZUMO GPS. The radio does not have NAV built into it. The Garmin/HD ZUMO you would have to buy and they are very pricy. Some do get the Garmin/HD one but others buy just a regular GPS unit that is available for as low as around $100. (US Dollars). I know of a few thay just use their smartphone GPS app.
2011 Merlot and Black TG.