WASHINGTON -- Weeks after announcing a massive recall, Japan's Takata Corporation told Congress it still doesn't know the cause of a potentially-deadly defect in its airbags -- or if the replacement parts are any safer.
The defect is linked to at least five deaths in the U.S. The recall impacts nearly 34 million airbags -- the largest auto recall in American history.
During a Capitol Hill hearing on Tuesday, Takata representatives were on the hot seat.
"In 2004, you identified the problem. You said that you could recreate the problem. You knew there was a problem," said Rep. Markwayne Mullin, R-Okla.
"And we thought we had a root cause at that time, too," responded Takata Executive Vice President Kevin Kennedy.
Many of the questions to Takata surrounded the chemical compound the company uses to fill its airbags, ammonium nitrate. The compound is thought to be unstable, especially when exposed to moisture, causing some of the airbags to explode with excessive force, sending shrapnel flying through vehicles.
Kennedy said the company is now "rapidly" transitioning away from ammonium nitrate. But says they're still not sure what, exactly, is wrong.
"Unfortunately, we have not yet got to a definitive root cause across all of these inflators," Kennedy said.
"If you don't have a root cause, how do you know the replacement parts that they bring in for the recall are not going to fail?" asked Rep. Brett Guthrie, R-Ky.
"Many of the replacement parts are different designs now," Kenendy explained. "About 50 percent of what we shipped last month were with our competitors' inflators, that do not use ammonium nitrate. That will go up to 70 percent here in the next months or so."
That means some airbags that have already been replaced will need to be replaced again.
"Some of these may not have the longevity that is needed to make sure that it's a lifelong, for the entire life of the vehicle, fix," said Mark Rosekind, head of National Highway Traffic Safety Administration.
NHTSA says they've gotten a list of vehicles from seven of the automakers affected by the recall, and they hope to have a full list within two weeks.
Even if that happens, it will still likely be years before all vehicles are fixed.