U.S. safety regulators have closed investigations into about 500,000 Ford Motor Co (F.N) and about 100,000 General Motors Co (GM.N) vehicles without calling for recalls, the National Highway Traffic Safety Administration said on Tuesday.

The Ford vehicles involved were 2004 to 2007 model year Ford Crown Victoria, Mercury Grand Marquis and Mercury Marauder vehicles, which were under investigation because a heat shield could rust, dislodge and cause the steering to jam.

NHTSA found the incidents occur rarely and six of the 10 reported complaints to the agency were from a single police department, which since it corrected its problem in 2011 has reported no further incidents.

The GM issue involved model year 2014 Chevrolet Impala sedans. The federal regulator received two complaints of unintended autonomous braking that resulted in rear-end collisions.

The Impalas were rental cars. GM investigators believe that the drivers in both incidents accidentally activated an electric park brake system, and that there was no evidence of problems with the autonomous braking systems.

For each of the moves, NHTSA said, "The closing of this investigation does not constitute a finding by NHTSA that a safety related defect does not exist."

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