Ford issued a stop-sale order to its dealers for the Mustang Mach-E electric crossover over concerns that a safety defect may render the vehicle immobile, CNBC reports.

The malfunction involves a potential overheating of the vehicle’s battery high voltage contactors, which can lead to the vehicle failing to start or losing power while in motion. It’s the latest hiccup to affect Ford’s rollout of its mass-market electric vehicle that has helped propel the automaker to second place in EV sales behind Tesla.

The affected vehicles include model year 2021 and 2022 vehicles built between May 27th, 2020, through May 24th, 2022, at the automaker’s Cuautitlan plant in Mexico — potentially every Mustang Mach-E produced so far. It’s unclear whether the automaker plans to also issue a recall. The latest recall for the Mustang, for unintended acceleration, is dated May 13th, according to the National Highway Traffic Safety Administration.

The stop-sale notice comes during a crucial time for Ford’s electrification strategy, with the first F-150 Lightning trucks reaching customers in recent weeks. The company reports selling 6,254 electric vehicles in May 2022, representing a 222 percent year-over-year increase and about 4.2 percent of Ford’s total sales volume. The Mustang Mach-E represents the bulk of those May sales, or 5,179 vehicles.

This isn’t the first speed bump in the Mustang’s short history. Ford was delayed in rolling out the EV in spring 2021 for extra quality checks. The automaker has also issued a handful of recalls for unintended acceleration, improperly attached seatbelts, and loose subframe bolts — amid other problems.

A spokesperson for Ford did not immediately respond to a request for comment.

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