Tesla is under investigation for failing to report crashes involving its partially autonomous driving technology in a timely manner.

The National Highway Traffic Safety Administration requires automakers to report crashes involving advanced driver assist features “within one or five days” of the incident, but Tesla was reporting crashes “several months or more” after they occurred, the agency said.

Tesla has told NHTSA’s Office of Defects Investigation that the delays were the result of a problem with its data collection that has since been fixed. But the agency is still opening an audit investigation as standard procedure to ensure the company is doing everything by the book.

The rule dates back to a standing general order (SGO) from 2021 that requires automakers and robotaxi companies to report crashes involving fully autonomous vehicles as well as Level 2 driver-assist systems. Under the SGO, companies are required to document collisions when an automated driving system was in use within 30 seconds of impact and report those incidents to the government.

Since it was implemented, Tesla has reported over 2,300 crashes to the federal government, according to NHTSA. An analysis of the crash data shows Tesla accounted for 40 out of 43 fatal crashes reported under the SGO.

Tesla’s Autopilot and Full Self-Driving features are considered Level 2 automated technology that requires full driver attention. By comparison, Alphabet’s Waymo uses Level 4 technology that doesn’t require a human driver.