This was the second time this year that Barra had appeared in front of Congress to testify about the ignition switch problem that has resulted in 13 deaths. Valukas is the author of a report released earlier this month on the ignition-switch recall. It criticized the culture at GM, but cleared Barra and other senior executives of attempts at a cover-up.

In a prepared statement released by GM, Barra highlighted the personnel changes made by the automaker, including firing 15 employees and adding 35 safety investigators.

Barra also reiterated the point she made in her town hall address two weeks ago: that GM staff should never forget about this period in the company’s history.

“I also told them that while I want to solve the problems as quickly as possible, I never want anyone associated with GM to forget what happened. I want this terrible experience permanently etched in our collective memories,” Barra said. “This isn’t just another business challenge. This is a tragic problem that never should have happened. And it must never happen again.”

“I will not rest until these problems are resolved,” she added.

Perhaps the most interesting moment of the morning came when Chairman Tim Murphy (R-Pa.) asked why Barra had fired only 15 GM employees following the Valukas investigation. He hammered home the idea that the number of firings represents an extremely small percentage of GM’s overall workforce, and wondered how the sweeping changes Barra promised could come without more personnel changes.

“If you haven’t changed the people how do you change the culture?” he said.

Barra doubled down on her assertion that these were the individuals who either had direct knowledge of the ignition switch problems and did nothing, or who moved too slowly to fix problems they knew about.

Diana DeGette (D-Col.), the ranking member of the committee, also went after the idea that only 15 people were responsible for the problems at GM.

She mentioned the “GM nod and salute,” the idea that employees would all nod in agreement at an assertion at GM, but not actually take action. DeGette asked Barra and fellow testifier Valukas if the 15 fired employees were the only ones guilty of “GM nod and salute.” Both agreed it was a more widespread problem.

Barra told the committee that the names of the 15 fired employees would be provided to them, but under the assumption of secrecy out of respect for employee confidentiality.

WATCH: 2014 is GM’s year of the recall