The National Highway Traffic Safety Administration (NHTSA) said Monday it is investigating whether Ford‘s 2022 recall of nearly 49,000 Mustang Mach-E electric vehicles sufficiently addressed issues and whether more vehicles should be included in the recall.

Ford recalled 48,924 of its 2021 and 2022 Mach-Es in June 2022 after concerns that high voltage battery main contactors may overheat from DC fast-charging and repeated wide-open pedal events. This could result in an immediate loss of propulsion power and cause an accident risk.

A battery main contactor is a high-current switch that controls the flow of electricity between the battery and the vehicle’s electrical systems, like the drivetrain.

At the time, Ford issued a free on-board software update to fix the issue, and then a technical service bulletin to replace the high voltage battery junction box on recalled vehicles. The software update involved monitoring the contactor temperature and reducing battery power to prevent damage to the contactor, and monitoring contactor resistance to find an overheated contactor and reduce vehicle power to prevent more damage.

NHTSA has now opened a recall query into 64,000 Mach-E vehicles after receiving 12 consumer complaints about vehicles that had received recall fixes. One owner in California told the U.S. safety regulator that the vehicle had a second catastrophic failure of its high voltage battery junction box just two days after receiving the software update.

Another Mach-E owner in Florida complained that shortly after charging at a DC fast charge station, the vehicle’s screen featured a pop-up message to “safely stop now.” The car came to a complete stop seconds later in the middle of a highway on-ramp. The driver had to wait several hours to restart the vehicle and only made it three miles before the car stopped again.