Tesla is facing scrutiny by federal regulators after a report that the electric car maker’s “Full Self-Driving” system may be linked to a fatal accident.

The National Highway Safety Administration (NHTSA) said in documents that it opened the probe on Thursday after the company reported four crashes, including one that killed a pedestrian, after Tesla vehicles entered areas of low visibility including sun glare, fog and airborne dust.

In addition to the pedestrian’s death, another crash involved an injury, the agency said.

Investigators will look into the ability of Tesla’s Full Self-Driving technology to “detect and respond appropriately to reduced roadway visibility conditions, and if so, the contributing circumstances for these crashes,” NHTSA said..

The investigation covers roughly 2.4 million Teslas from the 2016 through 2024 model years.

A message was left early Friday seeking comment from Tesla, which has repeatedly said the system cannot drive itself and human drivers must be ready to intervene at all times.

The agency also said it would look into whether any other similar crashes involving “Full Self-Driving” have happened in low visibility conditions, and it will seek information from the company on whether any updates affected the system’s performance in those conditions.

“In particular, his review will assess the timing, purpose and capabilities of any such updates, as well as Telsa’s assessment of their safety impact,” the documents said.

Last week Tesla held an event at a Hollywood studio to unveil a fully autonomous robotaxi without a steering wheel or pedals. CEO Elon Musk said the company plans to have fully autonomous vehicles running without human drivers next year, and robotaxis available in 2026.

“We’ll move from supervised Full Self-Driving to unsupervised Full Self-Driving, where you can fall asleep and wake up at your destination,” Musk said during the October 11 event. “It’s going to be a glorious future.”

The company also expects to make the Full Self-Driving technology available on its popular Model 3 and Model Y vehicles in Texas and California next year.

The unveiling of the Cybercab comes as Musk tries to persuade investors that his company is more about artificial intelligence and robotics as it struggles to sell its core products, an aging lineup of electric vehicles.

The splashy launch comes as Tesla struggles to drive sales and as Musk seeks to focus investor attention on the company’s robotics technology, including a humanoid robot dubbed Optimus. 

Tesla said earlier this month that it had deliver nearly 463,000 vehicles in the third quarter, up slightly from about 435,000 cars in the year-ago period.

Although Tesla remains the biggest U.S. manufacturer of electric vehicles, but faces mounting competition in its key markets around the globe, including Europe and China.