WASHINGTON - The National Highway Traffic Safety Administration said its Office of Defects Investigation has opened a probe into whether certain model year 2010 Ford Fusion vehicles have a defect involving wheel stud fractures. 

The agency said it is aware of four complaints alleging the problem. Three of the four vehicles cited in the complaints belong to the same 22-vehicle fleet but were assigned to different drivers who experienced the alleged defect on three separate occasions, NHTSA said. All four of the vehicles cited in the complaints had low mileage (between approximately 5,000 and 11,000 miles), and the wheels had never been serviced prior to the alleged incidents. 

The complaint vehicles were originally equipped with steel wheels and decorative wheel covers, with each wheel affixed to the vehicle via five lug nuts and wheel studs. At least one complaint alleges wheel stud fractures on multiple wheels, NHTSA said. Wheel stud fractures may result in wheel separation and loss of vehicle control.

 The agency has opened a preliminary evaluation to assess the alleged defect in the vehicles cited in the complaints. Such investigations help NHTSA determine whether a safety recall is at all warranted.