Quick diagnosis from Car Nerds and they ordered the part ,a hose assembly and 3 way check valve. I first went to Ford for the same problem and they kept the car 3 days and still did not localize the problem . I repeated bringing the car to ford 3 different times and paid for there brake inspection $150 with out a final diagnosis . Vacuum leak on the hybrid brake assist hose assembly . Car Nerds fixed it without blinking an eye. Worth a visit if you have an out of warranty hybrid .