The investigation involves 724,000 Ford Escape and Fusion, and Mercury Mariner and Milan models from model years 2009-11, which have generated 123 reports filed at the National Highway Traffic Safety Administration. The company, meanwhile, has received more than 1,400 complaints about engines that reportedly stall or lose power even at cruising speeds.
The engines do not technically stall each time. But the loss of power causes many drivers to assume the engine has shut down, The Detroit News reported Monday.
"We are cooperating fully with NHTSA on this investigation, as we do on all investigations," Ford spokeswoman Kelli Felker said.
Ford and parts company Delhi in October 2010 made adjustments to the manufacture of circuit boards considered the cause of the problem.
NHTSA said the problem was diagnosed trouble with electronic throttles that results in throttles stuck open and closed positions.
NHTSA said vehicles made from June 2009 to October 2009 may be outfitted with the faulty circuit boards. Cars made after Oct. 15, 2009, have circuit boards made by the newer manufacturing process.