Bad software turns some Mustang Mach-Es into ‘electric bricks’

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Charging is a common problem with electric vehicles. But some owners of the all-new Mustang Mach-E have run into a curious problem: their electric SUVs won’t start even when the main battery is full.

That is because, The edge has learned that there is a problem with some early Mustang Mach-E SUVs that has to do with how the much smaller 12-volt battery charges. It’s the latest in a growing series of minor issues that affect have come to light during the rollout of Ford’s first long-range electric car.

As with other electric cars, the Mustang Mach-E keeps up with its 12 volt lead-acid battery by essentially drinking power from the much larger lithium-ion battery pack. Based on owners’ accounts across multiple forum threads, including whoever spoke The edge, the problem is that this no longer happens when the Mustang Mach-E is plugged in to charge the larger battery pack.

That’s a particular problem for owners in cold weather areas, as Ford is encouraging them to keep their Mustang Mach-Es connected so that the SUVs can use electricity from the grid to heat up before driving.

The 12-volt battery powers many of the Mustang Mach-E systems (since the larger battery pack has high voltage), so the electric SUV cannot be started if it dies. When this happens, owners have reported that the FordPass app says the vehicle is in “deep sleep” mode. Some forum members are starting to refer to it as the “electric brick” problem.

Ford recently filed a technical service bulletin with the National Highway Traffic Safety Administration fixes the problem has to do with the software on the powertrain control module. Ford wrote that this only applies to Mustang Mach-E SUVs built on or before February 3, meaning it is possible that dozens have been affected. (Ford would only say a “small number” of the almost 7,000 Mustang Mach-Es delivered in the first three months of the year have the problem.)

At the moment, those owners cannot get the fix via a wireless update. The company said in a statement that they should take their Mustang Mach-Es to a dealer:

We are aware that a small number of Mustang Mach-E owners have had their 12V battery reach low voltage. We worked proactively with early owners who encountered this issue to identify the root cause and fix it. In the rare cases where this continues to happen, customers can now contact their local EV certified Ford dealer to resolve the issue.

Ford told it The edge that the problem could be addressed with a wireless update “later this year” and that the Mustang Mach-Es currently coming off the line should not be affected.

It is possible to jump on the 12-volt battery just like you would start a combustion engine car. But it’s nowhere near as easy, especially since the battery is located behind the Mustang Mach-E’s front trunk and the hood’s electronic lock is powered by the low-voltage battery.

To open the front trunk first, owners must open a panel in the front bumper which includes two cables, which can be used to jump over the front trunk electronic hood latch. They then have to pull back a panel under the hood to find the battery – although at this point some owners have had trouble accessing the cables from the 12-volt battery and cut through the vinyl to start the battery more easily.

Ford also offers free roadside assistance with the Mustang Mach-E, so owners have this as an option if they need to have their electric SUV towed to a dealer. Roadside assistance should also include the start of a 12-volt battery, according to the user manual

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Update April 8, 5:48 PM ET: Clarified in the tenth paragraph that owners discussed on Mustang Mach-E forums cutting through the trunk panels to access the battery more easily, rather than out of necessity.