DETROIT (AP) — A small maker of autonomous vehicle systems could be in hot water with U.S. highway safety regulators over how quickly it reported the crash of a test vehicle last fall.

The National Highway Traffic Safety Administration says in documents released Monday that it’s investigating Pony.ai’s reporting of an Oct. 28 crash in Fremont, California.

A software error caused one of the company’s test vehicles to crash into a median road sign. There were no injuries.

The agency says it opened the investigation to see whether Pony.ai complied with a June order requiring companies to quickly report crashes of autonomous test vehicles.

Poni.ai says it made a good-faith effort to comply with NHTSA requirements and has been cooperating with the agency.