I would do that first (unplug compass), if that doesn't do it then unhook the battery for 5 minutes and see if it's working after hooking battery up again. You may need to drive the car a little bit to calibrate the compass. I know for NAV they recommend something like 5 turns left 5 turns right with a vehicle speed over 25mph. I doubt that is necessary for just compass but you should know quick if that worked or not.