The National Highway Traffic Safety Administration has launched an investigation into a potential steering defect in Ford Fusion and Lincoln MKZ vehicles from the 2010 through 2012 model years.
The inquiry covers about 940,000 cars, including the Mercury Milan from the 2010 and 2011 model years.
The federal safety agency said it has identified 508 complaints alleging loss of power steering and the need for drivers to make an increased steering effort to control the cars. All of the vehicles have an electric power steering system.
In four of the complaints, drivers claimed that the steering assist failure contributed to loss of control of the vehicles and caused crashes.
Additionally, the agency said it has identified that there might be a problem from field data submitted by Ford.
Ford said it will cooperate with the investigators.
The NHTSA's Office of Defects Investigation said that in many of the complaints drivers said they saw a power steering warning message on the dashboard as the failure occurred.
In some cases, the condition was corrected by turning the vehicle off and restarting. However, many reports indicate the problem returned after restarting the cars. The agency's investigation will assess the scope, frequency and safety consequences of the alleged defect and whether Ford should recall the vehicles.
Automakers have already recalled a record 50 million vehicles in the U.S. this year, or about one of every five vehicles on the road.