DRIVING SLOWLY IN TRAFFIC, CAR IN FRONT STOPPED. I WENT TO STOP AND PUMPED BRAKE PEDAL SEVERAL TIMES BUT CAR WOULD NOT STOP. REAR ENDED CAR IN FRONT, STEERING WHEEL AIRBAG DEPLOYED AND ENGINE STOPPED. WENT TO MOVE CAR OUT OF TRAFFIC LANE AND AGAIN WHEN I WENT TO STOP, NOW GOING ONLY 3-5 MPH, PUMPED BRAKES AGAIN SEVERAL TIMES AND CAR WOULD NOT STOP. SAME THING HAPPENED ONE MORE TIME. THEN DROVE CAR TO RENTAL AGENCY USING HAND/EMERGENCY BRAKE ONLY, AND TRADED IN DAMAGED CAR FOR DIFFERENT ONE. DO NOT KNOW ANYTHING MORE ABOUT WHAT MIGHT HAVE BEEN FOUND WRONG WITH VEHICLE. *TR