VEHICLE WAS MAKING A RIGHT HAND TURN INTO A PARKING LOT AT APPROXIMATELY 15 MPH WHEN THE STEERING WHEEL JERKED TO THE RIGHT. THE RESULTING JERKING MOVEMENT/FEEDBACK RESULTED IN THE OPERATOR UNDER STEERING THE VEHICLE AND STRIKING A LARGE BOULDER ON THE SHOULDER OF THE PARKING LOT ENTRANCE. THE VEHICLE SUSTAINED MODERATE DAMAGE TO THE BUMPER, SKIRTING AND RIGHT FRONT FENDER. THIS VEHICLE HAD IT'S POWER STEERING RACK REPLACED LESS THAN 12 MONTHS PRIOR FOR THE SAME PERFORMANCE ISSUE. IN THE SUMMER OF 2010 GM REDESIGNED THE POWER STEERING RACKS FOR ALL LAMBDA PLATFORM VEHICLES (BUICK ENCLAVE, GMC ACADIA, SATURN OUTLOOK, AND CHEVY TRAVERSE) PRESUMABLY AS A RESULT OF COMPLAINTS LODGED BY CUSTOMERS DIRECTLY THROUGH DEALERS OR GENERAL MOTORS.