The federal government’s main auto safety agency said on Friday that it was investigating Tesla’s recall of its Autopilot driver-assistance system because regulators were concerned that the company had not done enough to ensure that drivers remained attentive while using the technology.
The National Highway Traffic Safety Administration said in documents posted on its website that it was looking into Tesla’s recall in December of two million vehicles, which covered nearly all of the cars the company had manufactured in the United States since 2012. The safety agency said that it had concerns about crashes that took place after the recall and results from preliminary tests of recalled vehicles.
The investigation adds to a list of headaches for Tesla, the dominant electric vehicle maker in the United States. The company’s sales fell more than 8 percent in the first three months of the year compared with the same period a year earlier, the first such drop since the early days of the coronavirus pandemic.
Tesla announced in December that it would recall its autopilot software after an investigation by the auto safety agency found that the carmaker hadn’t put in place enough safeguards to make sure the system, which can accelerate, brake and control cars in other ways, was used safely by drivers who were supposed to be ready at any moment to retake control of their cars using Autopilot.
The agency said it had identified at least 13 fatal crashes tied to use of Autopilot. The company is also facing lawsuits from individuals who claim the system is defective, and its design contributed to or is responsible for serious injuries and deaths.
The recall, which entails a wireless software update, includes more prominent visual alerts and checks when drivers are using Autopilot to remind them to keep their hands on the wheel and pay attention to the road. The recall covers all five of Tesla’s passenger models — the 3, S, X, Y and Cybertruck.
Tesla did not respond to a request for comment.
The auto safety agency also said Friday that it took issue with Tesla’s decision to allow customers to opt in to the recall and let them undo the changes. Tesla also appeared to issue other updates that addressed issues related to the recall that the company and the safety agency had not agreed on in advance.
“This investigation will consider why these updates were not a part of the recall or otherwise determined to remedy a defect that poses an unreasonable safety risk,” the agency said in its notice.
Tesla and its chief executive, Elon Musk, have long chafed at criticism of Autopilot and a more advanced system that it calls Full Self-Driving. They have argued that the systems, neither of which makes its cars autonomous, make its cars safer and have blamed any crashes or problems on drivers.
The carmaker has been under the scrutiny of safety regulators for other issues, too.
Last week, the auto safety agency said that Tesla had agreed to recall nearly 4,000 Cybertruck pickups. The agency said that the way soap had been used as a lubricant during the assembly of the truck could lead to the accelerator pedal becoming stuck. The carmaker is not aware of any injuries or accidents linked to that defect.
In February, Tesla recalled more than two million vehicles because the font size on a warning lights panel was too small.
These setbacks come as the company is struggling to hold on to its dominance in the electric-vehicle market as newer and more established automakers introduce new models around the world. Tesla’s market share in the U.S. electric-vehicle market fell to 51 percent in the first quarter, down from 62 percent during the same period last year.
Mr. Musk told employees this month that Tesla would cut more 10 percent of its work force. Two senior executives also announced that they were leaving the company.