Battery Management Software Updates

In a letter dated September 17, 2019, Mr. Edward Chen petitioned the NHTSA to initiate a defect investigation of certain Tesla Model S and Model X vehicles that received revised battery management software in one or more over-the-air (OTA) updates from Tesla, beginning in May 2019. The petitioner bases his request on vehicle fires that took place worldwide and OTA software updates Tesla made to the Battery Management System (BMS) of certain Tesla vehicles that resulted in loss of available vehicle mileage range and increased charging durations. On October 1, 2019, the Office of Defects Investigation (ODI) opened DP19-005 to evaluate the petitioner’s request. Information provided by Tesla in response to ODI's information request letter for DP19-005 indicated that a firmware update that may limit maximum voltage was installed in certain MY 2012 through 2016 Model S vehicles (subject vehicles). The voltage limiting firmware is a dynamic algorithm that is enabled in vehicles with high Supercharging use histories, which contributes to high usage stress to the high-voltage (HV) battery. Tesla sold approximately 61,781 subject vehicles in the United States and, through August 2021, the voltage limiting firmware had been enabled in approximately 2,062 vehicles. Through December 2020, ODI identified 59 complaints from consumers alleging reductions in battery capacity (52) or charging speed (7) in the subject vehicles. Log data from these vehicles showed that the voltage limiting firmware had been enabled in about 58 percent (30 of 52) of the complaints alleging range loss. Subsequent updates have restored some or all of the battery capacity to vehicles affected by the voltage limiting firmware coupled with updates enhancing BMS battery brick monitoring algorithms. None of the complaint vehicles have reported any thermal incidents or other safety hazards related to the HV battery. The five non-crash fires referenced in the petition include two fires that occurred in China in