The US National Highway Traffic Safety Administration has opened an investigation into a series of deadly crashes in which airbags in Hyundai and Kia cars failed to inflate.
The administration's Office of Defects Investigation (ODI) "is currently aware of six crashes with significant collision related damage events involving Hyundai and Kia models where air bags failed to deploy in frontal crashes," which killed four people and injured six, it said in document on its website.
The "failure of the air bag control unit (ACU) may prevent the frontal air bags from deploying in the event of a crash," it said.
Hyundai filed a report on the issue at the end of last month that led to a recall, but "has not identified a remedy."
The ODI investigation, which was opened Friday, will evaluate the scope of the Hyundai recall, determine if Kia and other manufactures are using the same or similar air bag control unit as Hyundai, and review factors that may be causing the failures, it said.
An estimated 425,000 cars may be affected by the issue.