The US National Highway Transportation Safety Administration announced it was investigating Nissan sedans for problems decelerating, and Chrysler pickups for transmission chain problems.
Nissan is being probed over 360,000 Nissan Versa and Versa Note vehicles manufactured between 2012-2014.
There were four reports that floormats kept a driver's shoe from decelerating as intended, the agency said.
In the Chrysler case, the NHTSA said it had received 15 complaints so far involving transmission chains and unintended stopping of vehicles.
It involves about 260,000 Dodge and Ram 1500 pickups made in 2005.