WASHINGTON — The nation’s top auto safety regulator opened an investigation this month into more than 120,000 Tesla Model Y crossovers from the 2023 model year after reports of steering wheels detaching while driving.

In a document made public Wednesday, NHTSA‘s Office of Defects Investigation said it was aware of two reports of “complete detachment of the steering wheel from the steering column while driving.”

Both vehicles were delivered to the owners with a missing retaining bolt that attaches the steering wheel to the steering column, the agency said in the document.

The steering wheels on both vehicles were removed and reinstalled.

“A friction fit maintained the connection between the steering wheel and the column splines during operation until separation,” NHTSA said. “Sudden separation occurred when the force exerted on the steering wheel overcame the resistance of the friction fit while the vehicles were in motion. Both known incidents occurred at low vehicle mileage.”

The agency opened the investigation — referred to as a preliminary evaluation — to assess the scope and frequency of the potential safety issue as well as the associated manufacturing processes.

In one complaint to NHTSA, a Tesla Model Y vehicle owner in New Jersey described driving along a U.S. highway when the steering wheel suddenly fell off. The owner said the 2023 model-year vehicle was purchased Jan. 24, and the incident happened just days later on Jan. 29.

The owner linked to a Twitter post, which now has more than 2.4 million views, allegedly showing the incident.

Most NHTSA investigations start as preliminary evaluations, in which agency engineers request information from the manufacturer, including data on complaints, injuries and warranty claims. The manufacturer also can present its view regarding the alleged defect and may issue a recall.

After the evaluation, NHTSA will either close the investigation or move into the next phase. If a safety-related defect exists, according to NHTSA, the agency may send a “recall request” letter to the manufacturer.

The latest safety probe comes as NHTSA continues another investigation into Tesla’s Autopilot driver-assist system after a series of crashes in the U.S. that resulted in more than a dozen injuries and one death.

In February, NHTSA prompted Tesla to recall nearly 363,000 U.S. vehicles equipped with or pending installation of its Full Self-Driving beta software as a result of the investigation.

Another investigation launched in February 2022 covers about 416,000 Tesla Model 3 and Model Y vehicles from the 2021-22 model years after NHTSA said it received hundreds of complaints alleging unexpected activation of the automatic emergency braking system, characterized by some Tesla owners as “phantom braking.”