The models under investigation include Hyundai's 2011 Sonata and Sonata Hybrid sedans, as well as Kia's 2012 and 2013 Forte sedans and Forte coupes. The agency says it has reports of six front-end crashes - there were four deaths and six injuries.
The NHTSA said it "will determine if any other vehicle manufacturers used the same or similar airbag control units, as supplied by ZF-TRW, and if so, evaluate whether the field experience of these vehicles indicates potentially related crash events".
Hyundai recalled almost 155,000 Sonatas after determining electrical overstress caused the airbags to fail to inflate in three of the crashes.
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Hyundai spokesperson Jim Trainor said dealers will consider offering a loaner auto to people until the issue can be repaired.
"We certainly would do everything we can to help our customers", Trainor said.
"We are actively investigating what exactly causes the airbag control unit to become damaged in these specific types of accidents", it said.
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ZF-TRW said in a statement that it is prevented by confidentiality agreements from identifying other automakers who bought its air bag control computers.
As airbag suppliers are different for the Sonata sedan sold in the USA and South Korea and the kinds of airbags are different for the Forte compact sold in the two markets, there have been no reported cases of airbag problems for Sonatas and Fortes sold in Korea and other markets, the spokesman said. Hyundai does not yet have a fix for the problem but said it expects the Sonata recall to start April 20.
The Korean companies said they're cooperating in the probe. The problem also can stop the seat belts from tightening before a crash. Agency documents show those vehicles had air bag computers made by ZF-TRW. ODI learned of two crashes via Vehicle Owner Questionnaires (VOQ) filed in 2015 and 2016, and all six crashes were reported via Early Warning Reporting submitted between 2012 and 2017.
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Four of the crashes in question involved Hyundai vehicles and two of the crashes involved Kia vehicles, the document states.