I know I'm jumping into the conversation rather late, and I apologize, in advance, for repeating something if it has been mentioned before. I tried to read my way through the previous comments and responses, but simply did not have enough time to make it through them all.
I, too, am having the same problem as many above - my camera and senors work just fine, but the grid lines no longer appear (mine is a 2011 Explorer with the non-active grid). Up until recently, the grid system operated just fine. I saw a lot of previous comments and responses where people indicate they began having this problem after having a component replaced (whether by a body shop and/or a Ford dealership). I, however, have not had any component of my rear-view camera system replaced or directly, negatively affected that I am aware of. The grids simply just stopped appearing one day, and yes, I have confirmed the setting is set to "on." I have also confirmed the software is up to date, and I occasionally witness the system perform "automatic maintenance" as normal. The zoom feature works fine, too.
I hesitate taking it to a dealership as I am rather confident they will not be of any help. I find most dealership service advisers and mechanics really don't know what they're talking about/what they're doing, and I usually have to advise them myself about something (keeping in mind, I teach elementary school; I'm not a professional in the auto industry). Contacting Corporate occasionally helps, but I have not yet tried that for this situation.
Any suggestions? Did I overlook comments that relate to my specific situation? Perhaps it's time to request assistance from Corporate. Thank you, in advance!