DETROIT -

General Motors CEO Mary Barra says she cannot tell "why it took years for a safety defect to be announced" regarding an ignition problem in the Chevrolet Cobalt and other small cars.

The statement is part of Barra's written testimony that she will present to Congress before a House subcommittee Tuesday and a Senate subcommittee Wednesday.

GM has recalled 2.6 million cars for a faulty ignition switch, which it links to 13 deaths.

Timeline: Major events in GM's recall of 1.6 million cars

"I will tell you that we will find out," Barra wrote. "When we have answers, we will be fully transparent with you, with our regulators, and with our

customers."

Download: Mary Barra's written testimony before House Committee on Energy and Commerce

In addition to Barra, David Friedman, the acting head of the National Highway Traffic Safety Administration, will also testify.

Download: NHTSA David Friedman statement before Committee on Energy and Commerce

In particular, Congress wants to know if it needs to strengthen a 2000 law intended to improve communication between automakers and the government. Fred Upton, a Michigan Republican who chairs the House Energy and Commerce Committee and announced the first hearing, wrote the law.

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