Two car fires have been reported to the federal agency. In each case the fire began near the battery on the driver's side in the engine compartment. NHTSA also is investigating 29 complaints of faulty air bag deployment in low speed accidents and air bags inflating when there was no collision.
Thermal gas from the air bags' deployment caused burns to 16 people, mostly on their hands. The air bag investigations covered 575,000 cars.
Federal auto safety officials also are investigating reports of faulty rear-wheel bearings in 2000 Focus models that potentially could cause lost of control of the vehicle. Ford Motor Co. called the investigations preliminary but said it was cooperating with government regulators.
"We are aware of the investigations and are cooperating fully with NHTSA," a Ford spokesman said.
The subcompact Focus, the world's most popular car, has been plagued by eight recalls since it was introduced in 2000. In November, Ford recalled 279,646 2000 and 2001 Focus models because of a corrosion problem from road salt that could cause the rear wheels to wobble.
Ford has sold 917,000 Focus models in two years and the two-millionth Ford Focus produced in Europe rolled off the assembly line in Germany last week.
On Monday, the Dearborn, Mich., -based automaker said it was repairing a quality control problem involving leaky head gaskets in some 5.4-liter V-8 F-Series truck engines. F-Series pickups from the 1999 model year may leak oil. Engine also was used in some full-sized Lincoln Navigator and Ford Expedition sport-utility vehicles and Econoline vans.
Separately, Ford said it would end production of the upscale Blackwood pickup next year because of poor sales. Ford had hoped to sell about 12,000 of the limited production luxury trucks but has sold just 379 since the Blackwood was introduced in November.