Federal safety regulators say that at least four people have died following head-on crashes in Hyundai and Kia cars in which the airbags did not deploy.
The National Highway Traffic Safety Administration said it's investigating the airbags in 2011 Hyundai Sonatas and 2012 and 2013 Kia Fortes after it received reports the devices failed to deploy in six different crashes that resulted in injuries, including the four involving fatalities.
There are an estimated 425,000 cars on US roads that could be affected by the problem, according to the NHTSA's review, which was made public on Saturday.
Hyundai announced earlier this month that it plans to recall 155,000 of the 2011 Sonatas due to a short circuit in the controller that deploys the airbags. But it has yet to recall the cars because it does not yet have a fix in place. The automaker said it will notify owners by April 20.
Hyundai's initial recall statement did not mention that any deaths or injuries had occurred in the cars with faulty airbags. When asked about the NHTSA's investigation, it said the four accidents involving Sonatas resulted in two deaths and two injuries. It described the accidents as "rare and unique."
"These accidents included a very high rate of speed and a severe offset head-on collision to the front driver side of the vehicle," said the company. "We are actively investigating what exactly causes the airbag control unit to become damaged in these specific types of accidents."
Kia, which is also owned by Hyundai Motors but operates as a separate company in the US, has not announced any recalls for the Forte related to the airbag. Kia said it is working with NHTSA but that it "has not confirmed any airbag non-deployments arising from the potential chip issue."
The airbags were made by ZF-TRW, according to the NHTSA filing. Spokespersons for VF-TRW did not respond to a request for comment.
The largest auto recall in the nation's history involved 50 million airbags made by supplier Takata for 37 million cars across most major automakers. Those airbags, which exploded and sent shrapnel into the car's occupants, have been tied to at least 13 U.S. deaths and more than 200 injuries, according to NHTSA.