]Air-bag maker Takata Corp. gave in to U.S. regulators on Tuesday, agreeing to what will be the largest automotive recall in history as investigators continue to search for the root cause of a defect that has killed at least six people.

About 34 million cars are now on a list for an air bag replacement, double the number that had already been recalled. With vehicles from 11 different automakers and a severe shortage of repair parts, it could take years for all the cars to be made safe, said Mark Rosekind, the head of the National Highway Traffic Safety Administration.

“As far as we know, this is the largest recall in auto history,” Rosekind said at a news conference in Washington. “Others are doing research and suggest that it could be one of the largest if not the largest of all of consumer recalls.”

As part of a consent order, Tokyo-based Takata agreed to make the recall nationwide and submit its parts to the U.S. government for testing. The agreement offers a way for Takata to resolve a global auto-safety crisis that made it a target for lawsuits and hurt the company’s standing with the automakers it supplies.

“We are pleased to have reached this agreement with NHTSA, which presents a clear path forward to advancing safety and restoring the trust of automakers and the driving public,” Takata Chief Executive Officer Shigehisa Takada said in a statement.

The company agreed to pay more than $1 million in accrued fines for it failure to cooperate with the investigation. Additional fines are possible.

Potential Fine

The case involves air-bag inflators that may deploy with too much force, breaking apart and sending shards of metal and plastic into the passenger compartment of vehicles. Takata, its automaker customers and U.S. regulators have had trouble getting to the root cause of the problem, and millions of customers are still unable to get their cars fixed because of a shortage of replacement parts.

“Takata should have been much more aggressive before now in protecting passengers through a national recall,” said Senator Richard Blumenthal, a Connecticut Democrat. “In the meantime the Department of Justice should be taking appropriate action to investigate and impose penalties.”

NHTSA has been pressuring Honda Motor Co., Nissan Motor Co. and eight other automakers affected by the recalls to speed the repair process and work with other air-bag suppliers to obtain parts. The agency also has demanded that Tokyo-based Takata turn over more documents and data from the devices that have been removed from the recalled cars.

Daily Fines

NHTSA in February began fining Takata $14,000 a day for not completely answering questions about air-bag inflater production and company efforts to investigate the explosions. It said at the time that most of the 2.4 million pages of documents the company had produced didn’t actually relate to the agency’s specific inquiries.

The agency become more aggressive since it was lambasted by Congress for failing to be more active prior to last year’s revelation that about 2.6 million General Motors Co. cars had a known ignition-switch defect that went unrecalled for years.

“NHTSA has done a 180-degree turn on how they’re handling these safety investigations,” Kevin Dean, who represents plaintiffs in several air bag lawsuits, said praising the agency. The recalls still may not go far enough, he said.

Ammonium Nitrate

Modern air bags, credited by NHTSA with saving more than 2,000 lives per year in the U.S., rely on small chemical reactions to safely inflate in milliseconds when sensors detect a crash. Takata’s trouble has been linked by safety advocates and victims’ lawyers to the company’s choice of chemical propellant, a type of ammonium nitrate that can be rendered unstable by high humidity and moisture.

In a properly operating device, gas created by an electrical charge is released through holes in a metal canister to inflate the air bag. If the chemical propellant tablets are made improperly or have degraded because of moisture, they vaporize with too much pressure, potentially resulting in a burst canister that hurls metal and plastic shards through the air bag and toward the driver and passengers.

“All of us have to do fact-checking to make sure they’re getting every vehicle with ammonium nitrate-based inflators, because they’re subject to deterioration over time,” Dean said.

National Recall

One of the main disputes between Takata and NHTSA had been over whether to initiate a national recall for some drivers’ side air bags. The company had said the defect was tied to high humidity, and it supported recalls limited to southern U.S. states with tropical weather.

Since then, all the automakers with cars that have Takata air-bag inflators have taken it on themselves to begin national recalls. There have also been recalls for defects in the passenger-sideair bags as well.

In addition to Honda and Nissan, Takata’s other affected customers in the U.S. market are units of Fiat Chrysler Automobiles NV, Toyota Motor Corp., Bayerische Motoren Werke AG, Mazda Motor Corp., Ford Motor Co., General Motors Co., Fuji Heavy Industries Ltd.’s Subaru and Mitsubishi Motors Corp.

Carmakers and parts suppliers face fines of $7,000 per day for not abiding by a U.S. law known as the Transportation Recall Enhancement, Accountability and Documentation Act, which requires the companies to tell regulators about customer injuries, lawsuits, warranty claims and complaints.

The maximum civil penalty is capped by Congress at $35 million. Because NHTSA issued two special orders to Takata, the company faces a combined fine of $14,000 a day, with a final maximum penalty of $70 million. The daily fines have been suspended as part of the consent order as long as Takata cooperates with the investigation.

“The penalties under the statute have been way too low,” Blumenthal said. “Either legislatively or judicially the laws should be reformed.”

–With assistance from Jeff Green in Southfield, Michigan, Chris Strohm in Washington and Margaret Cronin Fisk in Detroit.