Be sure the connectors go in fairly tight, if it is removed from your plane or yoke mounted it just could be making a bad connection into the unit from movement or regular wear, if you can, examine the connectors as you plug/unplug them. A small pick/screwdriver can spread them carefully to make a solid connection into the unit, once you get them solid a small drop of clear silicone on the connector can help to insure movement is kept to a minimum and can be removed easily if need be. Be sure to check the cables/antenna for kinks or extreme bends, this can cause problems as well. Ive had a 196 and a 496 and these are the most common problems with your issue, I dont belive a software issue is the cause. I hope this helps, Tough flying without these units !!