The traditional 12-volt battery that almost all vehicles have can go dead in Ford Mustang Mach-E EVs. It creates a no-start condition just as it would in any car. A “no-start condition” means you can’t start your car for you and me. Mach-E problems especially crop up in cold weather when the low-voltage battery goes dead
The problem is caused by how Mach-E charges the low-voltage battery
The problem is caused by how Mach-E charges the low-voltage battery. It doesn’t have an alternator like an ICE vehicle. So when the voltage in the battery starts dropping it taps into the high-voltage pack. The low-voltage battery pulls a minute amount of power from the high-voltage battery.
What’s happening is that when the Mach-E is plugged in to recharge the high-voltage battery it cuts off the trickle charge going to the lead-acid 12-volt battery. This especially happens in cold weather. That’s because Ford recommends you always leave the Mach-E plugged in during cold weather. This is so the high-voltage battery is fully charged for maximum range.
The problem as explained above is that when the high-voltage battery is being charged it cuts off power to recharge the low-voltage battery. Eventually, without replenishing the battery it goes dead. When that happens the FordPass app informs the owner their Mach-E has gone into “deep sleep” mode.
All Mach-Es built before February 3, 2021, are affected
Ford informed the National Highway Traffic Safety Administration the problem is because of “parameters in the powertrain control module.” The software problem only happens to early-production Mach-E Mustangs. All Mach-Es built before February 3, 2021, are affected.
The quick-fix requires owners to take their Mach-E into a dealer. Later this year an over-the-air update will cure the problem. “We are aware that a small number of Mustang Mach-E owners have had their 12V battery reach a low voltage condition,” Ford said in a statement to The Verge. “We proactively worked with early owners experiencing this issue to identify the root cause and a fix. In the rare instances where this still occurs, customers can now contact their local EV-certified Ford dealer to have the matter resolved.”
Until owners are able to schedule their Mach-E into a dealer they can jump the battery just as you would with an ICE vehicle. But with a dead battery, you can’t open the frunk to charge it. So owners will have to access a hidden compartment in the front bumper. Inside, a pair of leads can be jumped that allows you to open the frunk to directly charge the battery.