Federal regulators are investigating the air bags installed in 425,000 Kia and Hyundai vehicles after the devices reportedly failed to deploy in crashes in which four people died and six others were injured.

The National Highway Traffic Safety Administration began the investigation after air bags malfunctioned in six crashes involving four 2011 Hyundai Sonatas and two others in 2012 and 2013 Kia Fortes.

The NHTSA review began late last month after Hyundai notified the regulatory agency that “air bag control units showing that an electrical overstress condition of an . . . electronic component occurred in three of the crashes” and may have been a problem in the fourth Hyundai crash.

There was no information about where the crashes occurred.

The NHTSA review stops short of a formal recall of the vehicles, although it could lead to one. Hyundai opted to preempt any formal federal action by unilaterally recalling 154,753 Sonatas from model year 2011.

“Hyundai is aware of three rare and unique accidents where air bag control circuitry was confirmed to be damaged, and a fourth accident is under investigation,” the automaker said in a statement. “These accidents included a very high rate of speed and a severe offset head-on collision to the front driver side of the vehicle.”

Hyundai said it would seek to notify all owners of the recall before April 20.

Kia did not immediately respond to a Washington Post inquiry about its intentions.

In a statement to the news agency Reuters, distributed with an article on the NHTSA action Saturday, Kia said it “has not confirmed any air bag non-deployments arising from the potential chip issue.”

The issue is unrelated to the ongoing recall of nearly 34 million cars, the largest in U.S. history, because of air bags supplied by the Japanese firm Takata that exploded with a spray of shrapnel, killing at least 22 people worldwide and injuring hundreds more.

The air bags at issue in the NHTSA investigation announced Friday are manufactured by a German auto parts supplier, ZF Friedrichshafen-TRW, which confirmed it made the air bags on all of the approximately 425,000 cars in question.

“ZF is aware of the National Highway Traffic Safety Administration’s recently announced investigation,” the corporation said in a statement. “ZF continues to work with its customers and NHTSA to support the ongoing investigation.”