The investigations revolves around the deployment of airbags in the 2011 Hyundai Sonata and 2012-2013 Kia Forte models.
On Monday, Hyundai Motor’s share tread a downward slope following the opening of a probe by a U.S. regulator after some of its air bags failed to open in Kia Motors and its vehicles when they crashed which killed four people and injuring six others.
This is the second investigation by the U.S. National Highway Traffic Safety Administration into Hyundai Motor in less than a year.
The automaker is already grappling with weak sales in the United States.
The U.S. National Highway Traffic Safety Administration stated it was reviewing the 2012-2013 Kia Forte and 2011 Hyundai Sonata models, which encompasses almost 425,000 vehicles.
Last month, Hyundai Motor Co had issued a recall for more than 150,000 U.S. Sonatas after non-deployment reports were linked to electrical over-stress in the air bag control unit; the automaker stated it has yet to find a final fix to the issue.
A spokeswoman for Hyundai and Kia declined to comment on whether the recall will be expanded, saying the automakers were cooperating with the investigation.
According to the U.S. National Highway Traffic Safety Administration, the air bag control module was built by ZF Friedrichshafen-TRW, a German auto supplier which acquired TRW Automotive Holdings Corp in 2015.
Significantly, in 2016, a South Korean whistleblower had reported concerns that defects were concealed and that recalls were not issued in a timely manner to the NHTSA.