U.S. auto safety regulators have opened an investigation into Tesla’s Model Y SUV after getting two complaints that the steering wheels can come off while being driven.

The National Highway Traffic Safety Administration says the probe covers an estimated 120,000 vehicles from the 2023 model year.

The agency says in both cases the Model Ys were delivered to customers with a missing bolt that holds the wheel to the steering column. A friction fit held the steering wheels on, but they separated when force was exerted while the SUVs were being driven.

The agency says in documents posted on its website Wednesday that both incidents happened while the SUVs had low mileage on them.

Investigators look at how often the problem happens, how many vehicles were affected and at Tesla’s manufacturing process.

The Model Y is Tesla’s top-selling vehicle.