Traveling 65 mph on a freeway with adaptive cruise control (ACC) engaged, vehicle suddenly brakes hard on its own for no apparent reason; dropping 10 mph in a heartbeat. The vehicle did not produce a collision warning message on the dash. The cars in front of me were well beyond the longest 4 bar range of the ACC so it was not detecting and locked onto a car in front of me. There were no cars on either side, no car crossing in front of me and the road was flat with no obstacles. Fortunately, the car behind me was not tailgating as the sudden deceleration could have caused a rear end collision.

Sudden deceleration has happened twice during the six weeks I've owned this vehicle. I've also noticed that the ACC is inconsistent, often sluggish, in responding to the speed of traffic when it is detecting a car in front of me; creating additional hazard concerns for the driver.