Any one of the 4 cameras could cause this issue or an issue with the display module,to test measure voltage with a multimeter at the center pin of the coaxial connector on the camera, if 12v is found module is good, if not try an info reset using both outer steering wheel buttons, if voltage returns suspect camera, if not use a multimeter to check the cemter pin to the shielding for continuity, if connected suspect wiring, if not suspect module