The National Highway Traffic Safety Administration (NHTSA) is investigating allegations that the subframe on the Hyundai Sonata can corrode to the point of causing the suspension to fail.

The Office of Defects Investigation (ODI) at NHTSA has received 40 consumer complaints about severe corrosion in the 1999 through 2002 model year Sonatas.

Consumers have reported fist-sized holes in the frame that can cause the suspension control arm to detach from the vehicle, according to federal safety investigators.

The result can be wheel collapse or separation, half shaft detachment resulting in sudden vehicle disablement and or steering anomalies," according to the NHTSA Web site.

The federal agency has also received reports of corrosion in the engine cradle and front cross-member.

NHTSA said that there appears to be an increasing trend in failures, with 10 reported so far in 2008, 19 in 2007, 11 in 2006 and 1 in 2005.

Most of the complaints come from states where large amounts of salt are used on roads during snowy months, according to NHTSA.

The salt belt states according to NHTSA are Connecticut, Delaware, Illinois, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, West Virginia, Wisconsin and the District of Columbia.

Some consumers report discovering the severe corrosion during routine maintenance such as an oil change but the majority of the complaints allege that the corrosion was not detected until it resulted in suspension failure or a wheel came off, according to NHTSA.

Sonata owners reported traveling at speeds from 5 to 65 mph when they encountered the suspension failure. Some of the incidents resulted in the vehicle becoming disabled in the traffic lane at night with the driver and child stuck in the car, according to the NHTSA Web sit. Passing traffic swerved around the vehicle at high speeds, NHTSA said.

One consumer told federal safety regulators that the Hyundai Sonata was stuck in the middle of a dangerous intersection.

Another reported the sonata was so badly rusted the vehicle was declared a total loss by the insurance company after the lower control arm completely separated from the vehicle causing the half-shaft to detach from the transmission and resulting in damage to the wheel housing and quarter panel from the detached wheel.