A Tesla Model 3 electric car that was part of a fatal Southern California crash last week had the company’s Autopilot system activated when it careened into an overturned truck in the middle of the night, the Associated Press reported Friday.

The May 5 crash near Los Angeles is the latest of several that are playing into safety concerns for Tesla’s self-driving cars. It was the fourth U.S. death involving the Autopilot self-driving system, the newswire wrote. And it is sure to further complicate Tesla’s already-troubled relationship with transportation safety regulators.

Public affairs staffers at the National Highway Traffic Safety Administration (NHTSA) and the California Highway Patrol did not respond to requests for further information Friday afternoon. Tesla did not immediately respond to an emailed request for comment.

The investigation into the May 5 crash is the 29th probe NHTSA has initiated into crashes involving Tesla vehicles, according to information previously disclosed by the agency.

The investigation is likely to complicate Tesla’s attempts to gain broader market acceptance for its self-driving vehicles. There are concerns that the automated driving system is not ready for consumer use.

A coalition of competing automakers criticized Tesla’s vehicles as not truly autonomous because they still require an active driver. Tesla’s vehicles rely on an elaborate array of cameras and radar sensors to remain aware of the vehicles surroundings, as opposed to the lidar sensors employed by some other electric vehicles.

Tesla’s website and safety manuals do not describe Autopilot as a fully autonomous system, and they emphasize that drivers must be paying attention and ready to intervene.

The car is supposed to sense whether there is a person in the driver’s seat and act accordingly. But there have been several recent instances in which people have been caught allowing the car to drive completely on its own. On Tuesday, the California Highway Patrol arrested a man who was sitting in the back seat of his Tesla as it drove down the highway, according to the San Francisco Chronicle.

There have been numerous instances in which apparently distracted drivers failed to control Tesla vehicles at critical moments. In a 2018 incident, the driver of a Tesla model X SUV died in a crash near Mountain View, Calif., after accessing a video game on his phone. In another case, a Tesla’s sensing cameras failed to identify a truck’s white side against a brightly lit sky.

In mid-April, a Tesla crashed into a tree in a suburb outside of Houston, and it took firefighters four hours to put out flames fueled by the car’s battery pack. When the fire was out, they concluded that neither of the car’s two occupants had been in the driver’s seat at the time of the crash. A Tesla executive later broke with that official account and claimed that a person had been in the driver’s seat. A National Transportation Safety Board spokesman later said Tesla was “working with” the investigation but is “not a party” to it, a break with typical procedure that suggests a strained relationship between Tesla and regulators.