The car (#1) came to a sudden stop on a freeway without the driver stepped on the brake pedal. Front dash cam video on car #1 is available. Car #1 was then hit from behind by another car (#2) which could not stop in time. However, the impact was not significant because car #2 was able to partially switch lane and only the corners of the bumpers of both cars made the contact. The sudden stop problem could NOT be reproduced afterward by the driver. No dealer/car shop has been contacted on this issue. Warning light(s) status on dashboard of car #1 was UNKNOWN . However, driver of car#2 did report seeing brake lights of car #1 before the impact. Car #1 had never been in an accident before. This was the first time the sudden stop issue occurred.