Said control unit contains two integrated circuits where one could immediately overwrite data in the same memory address location that the other had just written to, resulting in a momentary failure. In case of multiple such events, the electric drive system will shut down, increasing the risk of a crash.

 

Denso is listed as the supplier of the battery control unit, with 89890-42381 being its part number. As per the recall documentation filed with the National Highway Traffic Safety Administration, the safety boffins at Toyota Motor North America started looking into this matter in August 2025, prompted by data observed during pre-production testing of a plug-in hybrid model.

At the time, Toyota determined that the same condition would not pose any problems to its battery-electric models due to a difference in the cycling of the monitoring circuit's write operation. The investigation concluded in September 2025, only to be reopened in April 2026 as part of a planned review.