Five car manufacturers have widened recalls of vehicles fitted with Takata Corp air bags.
The 34 million vehicle recall is the largest in US history, worldwide the call back has hit 53 million.
The air bags are at risk of exploding with so much force that metal fragments pepper the inside of the car.
The faulty safety system is believed to be behind six fatalities.
Car manufacturers, regulators and Takata have yet to identify the cause of the malfunction.
Fiat Chrysler, Honda, BMW, Ford and Mitsubishi are all involved in the recall.