DETROIT (AP) — U.S. auto safety regulators have expanded an investigation into malfunctioning air bag controls to include 12.3 million vehicles equipped with bags that may not inflate in a crash.

The problem could be responsible for as many as eight deaths.

Vehicles made by Toyota, Honda, Kia, Hyundai, Mitsubishi and Fiat Chrysler from the 2010 through 2019 model years are included in the probe, which was revealed Tuesday in documents posted by the National Highway Traffic Safety Administration.

It involves air bag control units made by ZF-TRW that were installed in the vehicles.

The control units can fail in a crash, possibly because of unwanted electrical signals produced by the crash itself that can disable an air bag control circuit housed in the passenger compartment, according to NHTSA documents. The electrical signals can damage the control circuit, the documents say.

ZF, a German auto parts maker which acquired TRW Automotive in 2015, said that it’s committed to safety and is cooperating with NHTSA and automakers in the investigation.

The case is another in a long list of problems with auto industry air bags, including faulty and potentially deadly Takata air bag inflators.

At least 24 people have been killed worldwide and more than 200 injured by the Takata inflators, which can explode with too much force and hurl dangerous shrapnel into the passenger cabin.

The inflators touched off the largest series of automotive recalls in U.S. history with as many as 70 million inflators to be recalled by the end of next year. About 100 million inflators are to be recalled worldwide.

On April 19, NHTSA upgraded the ZF-TRW probe from a preliminary evaluation to an engineering analysis, which is a step closer toward seeking recalls. So far, only Hyundai and Kia and Fiat Chrysler have issued recalls in the case.

Four deaths that may have been caused by the problem were reported in Hyundai-Kia vehicles and three in Fiat Chrysler automobiles. NHTSA opened an investigation in March 2017 involving the TRW parts in Hyundais and Kias.

The upgrade came after investigators found two recent serious crashes involving 2018 and 2019 Toyota Corollas in which the air bags did not inflate. One person was killed.

Toyota said it’s cooperating in the probe, doing its own investigation and will take “any appropriate action.”

NHTSA said it will take “appropriate action” based on the investigation’s findings.

Last year, Hyundai and Kia recalled nearly 1.1 million vehicles because of the problem, about a year after NHTSA opened its investigation.

Kia vehicles covered included 2010 through 2013 Forte compact cars and 2011 through 2013 Optima midsize cars in the U.S. Also covered are Optima Hybrid and Sedona minivans from 2011 and 2012.

Recalled Hyundai vehicles included 2011 through 2013 Sonata midsize cars and the 2011 and 2012 Sonata Hybrid.

In 2016, Fiat Chrysler recalled about 1.9 million vehicles worldwide including the 2010 Chrysler Sebring, the 2011 through 2014 Chrysler 200, the 2010 through 2012 Dodge Caliber, the 2010 through 2014 Dodge Avenger, the 2010 through 2014 Jeep Patriot and Compass and the 2012 and 2013 Lancia Flavia.