WASHINGTON (Reuters) - The U.S. National Highway Traffic Safety Administration is expanding a probe into potentially defective air bags to 12.3 million vehicles and upgrading it to an engineering analysis, a step required before it can seek to compel recalls, it said on Tuesday.

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The agency, known as NHTSA, said the air bags were installed in some vehicles from model years 2010 through 2019 sold by Fiat Chrysler Automobiles NV, Honda Motor Co, Hyundai Motor Co, Kia Motors Corp, Mitsubishi and Toyota Motor Corp.

The issue could be tied to as many as eight deaths.

They were equipped with an air bag control unit initially produced by TRW Automotive Holdings Corp, which is now owned by ZF Friedrichshafen. The agency said they could fail during a crash.

NHTSA opened a preliminary probe in 2018 of about 400,000 vehicles, and said on Tuesday it had reports of two crashes and two injuries related to the defect along with one death in a Toyota vehicle.

ZF spokesman John Wilkerson said the company “is committed to motor vehicle safety and is working cooperatively with NHTSA and our customers in the investigation.”

Toyota said it was “cooperating with NHTSA’s engineering analysis,” continuing its investigation into the issue and would take any appropriate action.

At issue is whether the air bag control units may suffer electrical overstress due to harmful electrical signals resulting from a crash, causing them to stop working during such an event. In opening its probe, NHTSA said “the probability of this occurring appears to be low.”

NHTSA noted Tuesday that two recent substantial frontal crashes may be tied to the issue. The agency is reviewing whether an “unreasonable risk exists that requires further field action.”

Hyundai, Kia and Fiat Chrysler previously issued recalls for more than 2.5 million vehicles with the TRW air bag control units in question that might not deploy in crashes.

When it recalled nearly 2 million vehicles for air bag non-deployments in 2016, Fiat Chrysler said it had reports of three deaths and five injuries that might be related to the defect.

The Center for Auto Safety said Tuesday that while deaths were first tied to the issue in 2016 “it has taken a higher body count for more significant action to be taken by NHTSA and most impacted manufacturers remain silent. The industry needs to do better.”

“When we became aware of this issue in 2016, we responded accordingly,” Fiat Chrysler said in a statement on Tuesday. “However, we will cooperate fully with NHTSA’s investigation.”

Hyundai and Kia ultimately recalled more than 1 million vehicles for air bag non-deployment concerns in 2018. Hyundai and Kia in 2018 said they had reports of four deaths and six injuries in North America tied to the issue.

Kia said it was unaware of any crashes or injuries involving any of its vehicles under investigation by NHTSA. Hyundai “continues to actively monitor the situation and is fully cooperating,” the company said.