National Highway Traffic Safety Administration (NHTSA) is investigating about 724,000 units of Ford's sports utility vehicles and crossovers in the US, over the limp mode problem.
The vehicles affected by the investigation include the Ford Fusion and Mercury Milan sedans along with the Escape and Mercury Mariner crossovers all with model years between 2009 and 2011, according to NHTSA.
Ford spokeswoman Kelli Felker said: "We are cooperating fully with NHTSA on this investigation, as we do on all investigations."
NHTSA said that depending on the condition of throttle control system malfunction, a driver may experience different levels of reduced engine performance.
Around 123 complaints have been registered by the NHTSA, while the car company had received 1,472 complaints regarding the issue.
In December 2012, Ford had recalled 19,106 units of the 2013 Fusion manufactured between February and October 2012, due to the defect in the coating of the low-beam headlamp projector which causes blurred lighting after prolonged use and may lead to accidents.
