The contact owns a 2018 Tiffin Phaeton RV. The contact stated that while driving approximately 60 MPH, the dashboard instrument cluster lights suddenly began to flash off and on and the Diesel Emission Fluid (DEF) sensor light remained illuminated before the vehicles decelerated independently to 5 MPH. The vehicle was driven to a nearby service center(unknown) and the Diesel Emission Fluid sensor was replaced, and the failure was remedied. The manufacturer was notified of the failure. The local dealer was not contacted. The failure mileage was 22,000.