ON MAY 13TH, APPROX. 11:10AM, CLEAR AND SUNNY 75F REDONDO BEACH, CA. I ENTERED THE VOLT TO BACK OUT DOWN A DOWNWARD SLOPING DRIVEWAY. I POWERED MY VOLT UP WITH FOOT ON BRAKE PROCEEDED TO SHIFT THE VOLT IN 'R'. AS SOON AS I RELEASED PRESSURE ON THE BRAKE PEDAL I STARTED TO MOVE DOWN THE DRIVEWAY AND PICKING UP SPEED. I APPLIED PRESSURE TO THE BRAKE PEDAL,WHICH FELT MUSHY. AND MY VOLT CONTINUED PICKING UP SPEED AND WOULD NOT STOP. I CONTINUED TO APPLY THE BRAKES, WHICH FELT VERY MUSHY, AND THE VOLT CONTINUED AND CROSSED THE STREET AND IMPACTED THE RESIDENCE DIRECTLY ACROSS TO FINALLY STOP MY VOLT. THE BRAKES FELT EXTREMELY MUSHY EXTENDING ABOUT TO THE FLOOR BUT NOT COMPLETELY TO THE FLOOR. WHEN THIS OCCURRED, I WAS IN BATTERY MODE BUT THE ENGINE WAS ENGAGED AND RUNNING AT HIGH RPM AND HEARD BY ME AND A PASSERBY WHILE THE VOLT WAS MOVING. I CALLED AAA TO PULL ME OUT. I WAS STUCK ON THE TREE AND FRONT STEPS. I CALLED IN THE INCIDENT TO MY INSURANCE COMPANY SO I COULD START THE CLAIM AND HAVE A CLAIM #. POLICE ARRIVED 40 MINUTES LATER TO TAKE A REPORT AND GIVE ME A FIELD SOBRIETY TEST. THAT WAS A LITTLE EMBARRASSING BUT GLAD IT WAS DONE. NOW IT'S DOCUMENTED THAT I WAS TOTALLY SOBER. I'VE READ 1-OR 2 THREADS REGARDING NON-OPERATING MUSHY BRAKES BUT NOTHING ABOUT A VOLT IN R COMING DOWN A SLOPE AND NOT BEING ABLE TO STOP. I CALLED ON-STAR TO SEE IF THEY HAVE A LOG OF CODES GENERATED FROM MY VOLT WITHIN THE LAST 24 HRS AND WAS TOLD NO. I AM VERY GRATEFUL THAT I DID NOT HIT ANOTH