The agency says it follows a report that a driver experienced complete loss of steering after the steering shaft detached from the steering wheel. The shaft also fell into a position that interfered with the driver's ability to apply the brakes.
The government says it's very concerned about the failure that occurred without warning on the two-month-old vehicle.
So far, no recall has been issued.
The preliminary investigation covers more than 50,000 2010 Kia Souls.
The multi-purpose vehicles have been marketed to urban drivers.