The NHTSA opened the Office of Defects Investigation into the air bag issue related to crashes in March.
According to the report, the software that operates the sliding door has an error that could affect the function of the doors.
Included are the 2010 through 2013 Forte, 2011 through 2013 Optima, and Sedona and Optima Hybrid minivans made in 2011 and 2012.
It was added that a few injuries caused by the issues have been reported.
The 2013 Forte crash took place in Canada.
The safety agency also said that electrical overstress appeared to be the root cause in a 2016 recall by Fiat Chrysler Automobiles NV of 1.4 million USA vehicles for air bag non-deployments in significant frontal crashes. The company does not have a fix for the issue yet but it is working with its supplier on the issue.
Kia spokesman James Bell said the company "is attempting to have a remedy by the scheduled owner notification date of July 27".
The carmaker said that the airbag control unit may short circuit as they are susceptible to electrical overstress.
ZF also supplies air bag computers to other manufacturers which it did not identify, but said each one is "designed to a customer's particular vehicle".
In May of a year ago, NHTSA opened an investigation into whether Hyundai and Kia moved quickly enough to recall more than 1.6 million cars and SUVs because the engines can stall, increasing the risk of a crash.