VEHICLE WAS PARKED ON TOP OF A HILL, TRANSMISSION IN PARK, KEY TURNED OFF. I SAT IN FRONT SEAT FOR SEVERAL MINUTES WHILE ENGINE WAS STOPPED AND TURNED OFF, I GOT OUT OF THE JEEP, OPENED THE BACK DOOR TO GET OUT SOME EQUIPMENT I WAS NEEDING FOR WORK. THE JEEP BEGAN TO ROLL DOWN THE HILL KNOCKING ME SIDEWAYS. IT WAS IN THE 2 WD POSITION. I COULD ONLY WATCH AS THE JEEP WAS HEADED FOR TWO LANE TRAFFIC, THIS IS THE SECOND TIME THIS JEEP HAS DONE THIS, SAME SCENARIO. BOTH TIMES THE WHEELS WERE ALL ROLLING, NOT SLIDING. I USED THE 4 WD EARLIER THE SAME DAYS, ON BOTH OCCASIONS BUT IT WAS IN 2 WD AT TIME OF ROLLING. HAD IT TOWED TO A JEEP DEALER GARAGE, THEY CANNOT DIAGNOSE IT, WOULD NOT ALLOW A RENTAL CAR, HAD TO LEAVE IT WITH DEALER TO FURTHER TRY TO "REPLICATE" AND DIAGNOSE. VERY DANGEROUS! BOTH EVENTS THE JEEP WAS ON A HILL AND ROLLED TOWARDS BUSY HIGHWAYS, THANKFULLY STOPPED ON OWN WITHOUT HITTING SOMETHING OR SOMEONE OTHER THAN ME ON THE SECOND EVENT. THANKFULLY NO CHILDREN/PETS/OTHERS WERE NEAR OR BEHIND THIS VEHICLE! *TR