WHEN THE BRAKE PEDAL WAS DEPRESSED IT FAILED TO STOP THE VEHICLE. THE PEDAL DIDN'T DEPRESS WHICH RESULTED IN CONSUMER'S VEHICLE REAR ENDING ANOTHER VEHICLE. DEALERSHIP INSPECTED THE BRAKES, AND INDICATED THAT THE POWER BOOSTER FAILED, AND A CHECK VALVE IN THE ANTI LOCK BRAKE SYSTEM FROZE UP. *AK