Barra is appearing before the House Energy and Commerce Committee and will be joined as a witness by the former U.S. Attorney Anton Valukas, author of a report released earlier this month on the ignition-switch issue that has been linked to 13 deaths. It called out the culture at GM, but cleared Barra and other senior executives of attempts at a cover-up.

Congressman Tim Murphy (R-Pa.), head of the subcommittee that will be questioning Barra, said on CNBC Wednesday morning that he is “not sure its enough to just say ‘take our word for it'” when it comes to changes to the culture of GM.

“This isn’t just that one or two people made a mistake one day,” he said. “How is she going to change that?

Murphy also called for “constant monitoring on several layers of supervisors.”

The testimony is scheduled to begin at 10 am ET.

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