WARNING: This page is about a different car, the 2013 Dodge Avenger and 2013 Chrysler 200. However, it is still accessible from the selected car via links, so may be relevant.
Possible Causes
TERMINAL DAMAGE OR CORROSION
(C515) REAR DEFOGGER CONTROL OUTPUT CIRCUIT OPEN
DEFOGGER GRID OR (Z917) GROUND CIRCUIT FOR THE GRID OPEN