If you switch from 20-inch wheels to something smaller for the winter, you may throw off your Nav system. I have 245/60/18 tires for the winter, and my Nav system stopped accurately positioning the vehicle as soon as the winter tires and wheels went on. The system basically became useless because it often showed the vehicle off-road.
Unlike a standalone GPS unit, it does not work solely off from satellites and instead gets input from the vehicle. It has taken several visits to the dealer to get this resolved. In theory, the system will recalibrate after 200 miles if your winter tires are close enough in size to the stock tires. Mine did not recalibrate last winter, but the vehicle also was subject to a TSB on Nav tracking. The other solution is to disconnect power to the GPS module by pulling the fuse or, if you are not a contortionist, disconnecting the battery. I pulled the negative battery cable for an hour, and the system immediately positioned the vehicle in my driveway instead of in the lake. It can now find its way home without getting lost.