US safety regulators have closed a pair of investigations into some 500,000 Ford Crown Victoria, Mercury Grand Marquis and Marauder sedans built between 2004 to 2007, and 100,000 Chevrolet Impala models from 2014.

The Ford investigation focused on rusting heat shields, which may become dislodged and jam the steering, according to Reuters. The National Highway Traffic Safety Administration found that this happened very rarely. In fact, of the ten incidents filed with the government safety watchdog, six came from a single police department, which evidently had some sort of problem with its reporting.

As for the Impala, the NHTSA investigators attributed two incidences of "unintended autonomous braking" to user error. In both cases, the vehicles were involved in rear-end collisions. According to GM investigators, it's believed that drivers accidentally activated the electric parking brake, causing the collisions. The vehicles in question were rental cars.

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