The contact owns a 2014 Toyota Prius. The contact stated while driving at an undisclosed speed, the vehicle failed to stop or decelerate as intended while the brake pedal was depressed. The ABS and service brake warning lights were illuminated. The contact added brake fluid; however, the failure persisted. The vehicle was taken to a local dealer where it was diagnosed; however, the cause of the failure was not yet determined. The vehicle was taken to a local Auto Zone, where it was scanned with an OBD2 scanner and DTC: C1391; was retrieved. The vehicle was not repaired. The manufacturer was notified of the failure and the contact was informed that the failure was related to an unidentified Toyota Campaign; however, the warranty had expired. The failure mileage was approximately 92,802.