An investigation into complaints that loose floor mats in some Ford Motor Co. Fusion, Lincoln MKZ and Mercury Milan cars may jam accelerator pedals was upgraded by U.S. regulators.

The National Highway Traffic Safety Administration, which regulates auto safety, today said it intensified a probe opened in May 2010 to an engineering analysis after receiving 52 complaints.

The investigation covers about 480,000 cars from model years 2008 to 2010, NHTSA said today on its website. Accelerator pedals may be stuck down by “unsecured or double stacked floor mats,” NHTSA said. No crashes or injuries have been reported, though some drivers said they had to shift into neutral or turn off the engine to slow down, according to the agency.

“We were disappointed by NHTSA’s upgrade of this investigation, particularly since the condition under investigation relates to improperly installed, unsecured or double stacked floor mats, but we will continue to cooperate fully with the agency through this process,” Susan Krusel, a Ford spokeswoman, said.

NHTSA’s Ford investigation shows the regulator is continuing to learn about instances of unintended acceleration, similar to reports that plagued Toyota Motor Corp. in 2009 and 2010. Asia’s largest automaker recalled more than 10 million cars and trucks worldwide after complaints that resulted in congressional hearings.

“It’s certainly a red flag,” Philip Reed, senior consumer advice editor for auto researcher Edmunds.com, said in an interview. “NHTSA takes it very, very seriously.” 

(Bloomberg)