The National Highway Traffic and Safety Administration rejected a 2019 petition requesting the agency open a formal investigation into Tesla's battery management software over allegations that an over-the-air update was defective and caused fires in five vehicles.
The agency decided not to open a formal investigation in part because the majority of those incidents occurred outside of the United States, according to a document posted on its website. None of these were related to crashes and most were parked.
As part of its evaluation, NHTSA reviewed 59 complaints out of the total 61,781 Model S and Model X vehicles from 2012 to 2019 included in the petition before it decided to reject it. Out of the 59 complaints, 52 alleged reductions in battery capacity and seven alleged reductions in charging speed after the software was updated. Log data from the vehicles showed that the voltage limiting firmware was enabled in 58% of the complaints, but that subsequent updates restored some or all battery capacity to those vehicles, according to the report summary.
The agency did find that a perfect storm caused two of the fires that occurred in China in 2019. The vehicles had recently completed fast-charging sessions, the batteries were at a high state-of-charge and were parked with the battery cooling systems shut off. The two vehicles also had histories of high-stress usage.
Sources familiar with Tesla's battery management system say if there were truly a systematic software issue, way more than five cars would have caught fire. The more likely causes of such infrequent issues would be physical defects from manufacturing or physical damage in the course of use, like putting recently Supercharged vehicles under high stress, which NHTSA says is more common in China where those fires occurred.
There were also two fires that occurred in the U.S., but one involved a vehicle with no Supercharging history that was driving at the time of the fire, and another that couldn't be linked back to the high-voltage battery system. The fifth fire happened in Germany with a vehicle that had been parked at a low state of charge for an extended period of time.
"Given the absence of any incidents in the United States related to fast charging, and the absence of any such incidents globally since May 2019, it is unlikely that an order concerning the notification and remedy of a safety-related defect would be issued due to any investigation opened as a result of granting this petition," the petition concluded. "Therefore, upon full consideration of the information presented in the petition, and the potential risks to safety, the petition is denied."
The report did say that the agency would take further action if warranted, despite the denial of this current petition, if future findings identify safety-related defects.
Even as NHTSA rejects this petition, it is still moving forward with a different investigation into Tesla's Autopilot software after certain cars that had activated the advanced driver assistance system crashed into 12 parked first responder vehicles with flashing lights, resulting in 17 injuries and one death since 2018. Tesla has until October 22 to hand over detailed Autopilot data or face fines up to $115 million, a slap on the wrist, really, considering the company's second quarter net income of $1.14 billion.