DETROIT — The U.S. government’s auto safety agency is investigating whether last year’s recall of Tesla’s Autopilot driving system did enough to make sure drivers pay attention to the road.

The National Highway Traffic Safety Administration says in documents posted on its website Friday that Tesla has reported 20 more crashes involving Autopilot and since the recall. The crashes and agency tests raised concerns about the effectiveness of the remedy. The recall involved more than 2 million vehicles, nearly all the vehicles that Tesla had sold at the time.

The agency pushed the company to do the recall after a two-year investigation into Autopilot’s driver monitoring system, which measures torque on the steering wheel from a driver’s hands. In the probe, the agency was looking at multiple cases in which Teslas on Autopilot ran into emergency vehicles parked on freeways.

The recall fix involves an online software update to increase warnings to drivers. But the agency said in documents that it has found evidence of crashes after the fix, and that Tesla tried to address problems with additional software updates after the recall fix was sent out. The updates may not have worked.

“This investigation will consider why these updates were not part of the recall or otherwise determined to remedy a defect that poses an unreasonable safety risk,” the agency wrote.

A message was left seeking comment from Tesla.

NHTSA said Tesla reported the 20 crashes in vehicles that had received the recall software fix. The agency has required Tesla and other automakers to report crashes involving partially and fully automated driving systems.

NHTSA said it will evaluate the recall, including the “prominence and scope” of Autopilot’s controls to address misuse, confusion and use in areas that the system is not designed to handle.

It also said Tesla has stated that owners can decide whether they want to opt in to parts of the recall remedy, and it allows drivers to reverse parts of it.

Safety advocates have long expressed concern that Autopilot, which can keep a vehicle in its lane and a distance from objects in front of it, was not designed to operate on roads other than limited-access highways.

The investigation comes one week after a Tesla that may have been operating on Autopilot hit and killed a 28-year-old motorcyclist near Seattle.

After the April 19 crash, the 56-year-old driver of a 2022 Tesla Model S told a Washington State Patrol trooper that he was using Autopilot and looked at his cellphone while the Tesla was moving.

Authorities said they have not yet independently verified whether Autopilot was in use at the time.

On Thursday, the NHTSA ended its investigation of Autopilot, citing the recall and the inquiry of its effectiveness. The agency said it found evidence “that Tesla’s weak driver engagement system was not appropriate for Autopilot’s permissive operating capabilities.”