Open the Radio lid and inside is a disk slot. Press eject and see if there is a Nav Cd in there. If not, you need one. I'm not sure what type of Nav system you have as there is a CD and DVD based system. DVD is newer, however I'm not sure what year ML's starting production with them. Perhaps someone else can chime in? Any of the disks can be purchased from a dealership.

__________________
Steve32