On its website, the National Highway Traffic Safety Administration upgraded an investigation into Ford Windstar minivans following numerous complaints about corrosion in the vehicles.
NHTSA recently launched an engineering analysis - an advanced stage of its ongoing investigation - that covers about 550,000 Windstar minivans from the 1999-2003 model years.
Ford has recalled more than 600,000 of the minivans in Canada and the United States because rear axles can corrode and break. NHTSA said its latest probe focuses on new corrosion complaints in the front of the vehicles.
In the U.S., the recall began in August 2010 and is limited to 22 northern states where salt is used to treat roads during the winter.
NHTSA said it has received 346 complaints of corrosion and broken front sub-frames on the Windstar. The sub-frame supports the Windstar's engine, steering rack, transmission and front suspension.
Steering control on the Windstar can be impeded if the sub-frame is cracked or excessively corroded. One injury and three crashes have been reported to NHTSA, which said that most of the latest complaints have been filed by motorists in cold weather states.
NHTSA added that some Windstar owners have also cited problems on the right side of the vehicle with the routing of air-conditioning lines.