Regulators are investigating a problem where Tesla cars randomly slam on the brakes at highway speeds

• US regulators have opened an investigation into Tesla's "phantom braking" problem.
• Owners have reported their cars randomly slam on the brakes at highway speeds for no reason.

A US government agency said Thursday it had opened an investigation into Tesla over complaints from consumers that their cars sometimes slam on the brakes unexpectedly.

The National Highway Traffic Safety Administration said it has received 354 complaints in the last nine months about the issue, known as "phantom braking." According to the complaints, Teslas have been suddenly, aggressively braking — sometimes at highway speeds — unsettling drivers and nearly causing collisions.

NHTSA said phantom braking occurs when owners use cruise control or Autopilot, Tesla's driver-assistance system that brakes, accelerates, and steers on the highway. The agency is conducting a preliminary evaluation of the problem, which may affect an estimated 416,000 Model 3 sedans and Model Y SUVS from the 2021 and 2022 model years.

The Washington Post reported about a rise in complaints about phantom braking earlier this month. Tesla did not respond to Insider's request for comment.

Most new cars, including Teslas, come with an emergency braking feature that uses sensors to stop the car when a crash is imminent. It appears that Teslas are activating emergency braking for no reason, sometimes confusing nearby vehicles or shadows for dangerous obstacles.

Rubin Sandhu, who bought his Model 3 Performance in December, told Insider he was using Autopilot when an RV passing in the opposite direction caused his car to quickly slow down from around 80 mph to below 40 mph. He said he had to swerve into the oncoming traffic lane to avoid getting rear ended by a Toyota Tundra pickup truck that was following close behind. He told his 17-year-old son, who drives the Tesla sometimes, not to use Autopilot after that.

Safety regulators have dialed up scrutiny of Tesla as of late. The company is under investigation for a dozen incidents in which vehicles with cruise control or Autopilot turned on collided with stopped police cars and fire trucks. It's also issued several recalls in just the last few months, some of which have been fixed with remote software updates.