Last year, Ford issued a recall for almost 49,000 Mustang Mach-E crossovers due to a problem with the electric vehicles’ high-voltage battery contactors. The automaker’s fix was a software update to two control modules on the Mach-E, but on Monday Reuters reported that the National Highway Traffic Safety Administration’s Office of Defects Investigation has opened a recall query to see if Ford’s software recall actually did the job.
On June 21, 2022, Ford issued a recall for 48,924 Mustang Mach-Es, also instructing dealerships to stop delivering the EVs to customers until the software fix was ready. The problem was battery contactors that could overheat during DC fast charging or with repeated use of full throttle; that overheating could lead to either arcing or the contact surfaces deforming, which in turn could lead to a complete loss of power while driving.
According to the recall safety notice, Ford had 286 warranty claims for open or welded contactors between July 2021 and May 2022. Ford’s fix was a software update to the secondary on-board diagnostic control module and the battery energy control module.
The new software didn’t actually fix the contactors, but it does monitor contactor temperature and resistance and can reduce battery power to prevent contactor damage should either of those fall out of range. Ford also issued a technical service bulletin to replace the high-voltage battery junction box in Mach-Es that had been given the new software but still suffered a loss of propulsion due to this defect.
But NHTSA has received 12 post-recall complaints from Mach-E customers alleging the fix did not work. A Mach-E owner from Sunnyvale, California, reported having to have two high-voltage battery-junction boxes replaced in the span of three months. Another owner reported having a permanent loss of power while driving at 70 mph in Texas. A Mach-E owner in Honolulu, Hawaii, told NHTSA their car lost power and the steering seized while driving a software-updated Mach-E.
“As I was driving to merge onto the freeway my screen panel said “safely stop now”, with a turtle logo and battery icon coming on. My car then came to a complete stop within a few seconds in the middle of the on-ramp leaving me stranded. I repeatedly tried to turn the car on and off to see if I could get it to accelerate again but to no avail. I had no time to pull my car over since it died immediately,” wrote a Mach-E owner from Hercules, California.
The most recent complaint cites an incident that happened on June 8, 2023, in Mandeville, Louisiana. In this case, a Mustang Mach-E suffered a loss of power and died on a busy highway off-ramp.
NHTSA’s ODI is not the only investigation into the Mach-E battery contactor recall. Last July, three owners sued Ford in federal court over the defect, alleging that Ford’s software update was not a “true solution to the battery/overheating issue.”
Ars contacted Ford for a comment and will update this story as and when it replies.