The federal government has added the Mercury Milan to an investigation into reports of wheel studs breaking on some 2010 model Ford Fusion sedans.
The National Highway Traffic Safety Administration says the investigation now affects more than 317,000 of the midsize sedans, which are essentially the same car.
Wheel studs are the bolts that hold the wheel to the car. The agency has received 29 complaints about the studs breaking, including four cases of wheels becoming separated from the car.
The government says there have been no crashes or injuries reported.
The complaints involved vehicles with low mileage of 5,000 miles to 11,000 miles.
The government began investigating the problem with 280,000 Fusions in January. It says Ford is looking into the cause. The cars haven't been recalled.