the disc does not determine your route... the settings in your system menu detiermines which route will be calculated. make sure you don't have roads designated to avoid. Like for instance they have turned a road into a toll road here in my area since the last dic, and since I have toll roads set to avoid, even the FREE section of the hwy gets avoided by the system when calculating routes. I had to turn off toll road avoid to get it to start routing my on "shortest" route again.
My $0.02.