The National Highway Traffic Safety Administration is studying electrical fires in about 1.4 million Toyota models, an increase of nearly 600,000 cars since the agency opened the investigation in February.

Consumer complaints from actual crashes allege that fires and burning smells originated in the driver's side power-window switches. As a result, NHTSA is studying these switches found in certain 2007 to 2009 Camry, Yaris, and RAV4 models, plus all 2008 Highlander models. So far, the agency has recorded 161 complaints of fires and nine related injuries. No fatalities have been reported. NHTSA investigations do not necessarily lead to a recall.

In an April 25 letter to NHTSA responding to the investigation's initial 830,000 cars, Toyota said that aftermarket lubricant covering the faulty window switches -- sprayed by dealers or owners in an effort to alleviate sticking switches -- likely caused the fires.

However, in 2009, Toyota recalled certain 2007 and 2009 Camry and 2009 Yaris models built in China for potential fires in the driver's side power-window switches. In this case, "excessive grease application" at the factory could cause a fire in which "air gaps between contact points in the contact module could be filled with this grease and lead to a short circuit."

Toyota also recalled the 2006 Vitz (Yaris) in Japan for similar issues that same year. In its letter, Toyota said that while the components were "substantially similar" to those in U.S.-spec vehicles, the suppliers and manufacturing techniques in China and Japan were different enough to not warrant a recall in the U.S.

"We will continue to cooperate fully with the agency in its evaluation," said Toyota spokesman Brian Lyons in an e-mail Monday.

Last week, NHTSA expanded two other fire-related investigations, one involving about 342,000 Chevrolet Trailblazer SUVs and associated models for possible door-panel fires and another involving 5.1 million Jeep Grand Cherokee models for possible gas-tank fires.

[Source: NHTSA via USA Today.]