It was stop and go traffic. I was distracted and the car failed to auto stop and I hit the car in front of me. The alert did come on after the collision. I would assume the automatic braking failed or the collision would not have occurred. It was a low speed impact so not a major safety risk but even a minor collision can have a significant injury in susceptible subjects? The problem has not been reproduced to my knowledge. The component has not been inspected. The car has been evaluated by a body shop for damages and the damages are significant. The warning light came on in an inadequate time to prevent the collision. There were no other warning lamps