I do not have experience with that particular model, but on the JV33, the media width sensor sticks out from under the carriage and left of the head (if your facing the printer.) I have had head strikes that change the position or angle of the sensor resulting in a bad reading. Take a look under the carriage and make sure the sensor is pointing straight down.
Two plastic tabs hold it in place, and they break easily...I have one unit with a media width sensor held in place with tape.
Hopefully that's all that's wrong with your printer, as the part is cheap, or can usually be fixed with tape.
Good Luck!