Ford, NHTSA investigate wheel studs on Fusion, Mercury Milan

The National Highway Traffic Safety Administration has upgraded an investigation into complaints about the 2010 Ford Fusion and Mercury Milan sedans to an engineering analysis, one step closer to a recall.

The investigation of 317,315 cars results from claims of fractured wheel studs, which could cause a wheel to come off.

Ford's investigation is ongoing and no recall has been announced.

"We'll fully cooperate with the government as they review this matter," said Wes Sherwood, Ford spokesman. "We are not aware at this point of any allegations of injuries related to this matter."

There have been 29 complaints and 128 warranty claims related to the issue, according to NHTSA, with four reported incidents of a wheel separating from the car.

The engineering analysis follows a preliminary investigation, which may or may not lead to a recall.

By Jake Lingeman