Ford Motor Company has told federal safety regulators that a software defect can make dozens of Mustang Mach-E electric SUVs overstate how healthy their own high-voltage batteries are, a miscalculation that can trigger sudden power loss or, after repeated fast charging, a battery fire. The National Highway Traffic Safety Administration logged the case on Sept. 9, 2026, covering 2023 through 2025 model-year Mach-Es built between July 3, 2023, and Aug. 26, 2025.
The problem does not sit in the batteries Ford installed at the factory. It sits in the module that watches over them after a dealer swaps one in, and in the number that module hands back to the driver.
A replacement module that starts out lying about its own health
Every Mach-E with a lithium iron phosphate pack relies on a Battery Energy Control Module, or BECM, to track state of health, the running estimate of how much usable capacity a battery has left. Ford’s filing, recorded by NHTSA under campaign 26V582, says that when a dealer installs a replacement BECM, the new module fails to inherit the pack’s actual, already-degraded state of health and instead initializes the reading at a flat 100 percent, as though the battery were brand new.
That single miscalibration cascades. A battery reporting full health when it is not lets the vehicle’s software push the pack harder than its real condition allows, and it throws off the safety logic built to intervene before things go wrong. Ford’s own consequence language, filed with the agency, is direct: “the software may cause an incorrect state of charge to display in the vehicle, or lead to an increased risk of a high voltage battery fire after repeated DC Fast Charging cycles.”
Lithium plating and the thermal-venting pathway
The mechanism runs through a well-known failure mode in lithium batteries called lithium plating, in which metallic lithium builds up on a cell’s anode instead of intercalating normally rather than storing charge the way the chemistry intends. A NHTSA technical review of lithium-ion safety describes exactly this pathway, warning that cells pushed outside their normal charging window can develop plating that turns into dendrites capable of piercing a cell’s internal separator, and that once that failure process starts it is “not self-limiting” without active battery-management controls stepping in. Autoevolution, which obtained additional detail on the Mach-E recall, reported that the plating creates a potential thermal venting condition inside the affected cells, the precursor state to a battery fire, once the miscalibrated state-of-health reading has let a degraded pack keep accepting fast-charge sessions it should have been throttled away from.
Owners have one practical early warning. A wrench light or the Mach-E’s turtle telltale appearing in the instrument cluster during a reduced-power event is the dashboard signal that the BECM has likely triggered a power-limiting response tied to the defect. Ford’s filing does not describe the warning as a substitute for the recall repair, only as a symptom that can appear before it, and it gives owners no diagnostic step to take on their own beyond scheduling service.
NHTSA’s record lists no crashes or injuries tied to the defect as of the filing date. Ford’s own count is similarly narrow: one warranty claim, one customer contact and two quality-indicator reports flagged the issue inside the United States before the automaker moved to a recall rather than a quieter service bulletin.
A narrow population, and a remedy still weeks from arriving
Just 86 vehicles carry the defect nationwide, a small population even by the standards of a niche EV like the Mach-E, because the flaw only reaches a car once a dealer has already replaced its original BECM under separate service work. Ford has not yet published the software fix. Interim letters, which by federal rule must tell owners a remedy is coming without yet offering one, are scheduled to go out between Oct. 26 and Oct. 29.
Owners will not get a second letter inviting them to a dealer until Ford finishes validating the update, with remedy notifications projected for late December. The eventual fix, once available, adds a data-migration step so a replacement BECM pulls in the battery’s true, already-degraded state of health rather than assuming the pack is new, and Ford says dealers will install it at no cost.
NHTSA maintains a broader VIN-based recall lookup tool that lets any Mach-E owner check within seconds whether a specific vehicle carries an open campaign, including this one, without waiting for a letter to arrive. The agency has also been tracking fast-charging and battery-health diagnostics as standing research priorities under its Battery Safety Initiative, the program through which it coordinates lithium-ion fire investigations across manufacturers rather than treating each recall as an isolated event.
Owners waiting on the fix are left with a narrower version of a familiar EV-ownership problem: a dashboard number meant to be the most trustworthy figure in the car, degrading gracefully as a battery ages, has instead been reset to a false 100 percent by the very repair meant to restore it.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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