BUMPER TO BUMPER TRAFFIC ON FREEWAY LES THAN 5 MPH TRAFFIC SUDDENLY STOPPED I DEPRESSED BRAKE AND VEHICLE DID NOT STOP. SLIGHT REAR END COLLISION RESULTED. A SECOND AND SIMILAR TRAFFIC CONDITION RESULTED AT LOW SPEED THE BRAKES DID NOT STOP THE VEHICLE APPROPRIATELY. I HAD TO FULLY DEPRESS THE BRAKE PEDAL AND THE VEHICLE SLOWLY CAME TO A STOP. THE VEHICLE APPEARS TO BE ACTING LIKE IT DOESNT HAVE 'POWER' BRAKES.