We can't just take GM's word for it: GOP lawmaker

Rep. Murphy: GM's corporate culture at crux of recall

General Motors' internal investigation into the ignition-switch recall crisis resulted in so few firings and changes that it's hard to believe the automaker's corporate culture could already be on the mend, Rep. Tim Murphy told CNBC Wednesday ahead of a hearing before his subcommittee.

"I'm not sure it's enough just to say, 'Take our word for it. We're going to put these recommendations in place.' And after changing less than 1/100th of 1 percent of the employees, things are going to be different," the Pennsylvania Republican said on CNBC's "Squawk Box."

In addition to lawmakers, the Justice Department and other authorities are investigating why the automaker waited more than a decade to recall 2.6 million Chevrolet Cobalts and other small cars with that ignition-switch flaw now tied to at least 13 deaths.

"This isn't just one or two people who may have made a mistake one day and a slip-up occurred," said Murphy, adding he wants to know how GM chief executive Mary Barra plans to change the culture that "made this pervasive despite lots of warnings signs."

At last week's annual shareholders meeting, Barra said she has no plans for more dismissals, as a result of the company's internal recall investigation. Earlier this month, 15 employees were fired and five others were disciplined for failing to catch or flag the switch problems.

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Rep. Murphy: Drivers should take GM recall notices seriously

"Anybody who drives a General Motors car, one should take very seriously those recall notices, especially with the switches," said Murphy, who chairs the House Commerce Committee's subcommittee on Oversight and Investigations.

Barra will be joined at Wednesday's hearing by former U.S. Attorney Anton Valukas, who conducted the months-long investigation that revealed deep flaws in the automaker's internal decision-making process and made recommendations on how to fix things.

On Monday, GM recalled an additional 3.36 million midsize and fullsize cars, because of an ignition switch problem similar to the previous recall. Eight crashes and six injuries have been tied to this new issue.

Read MoreGM recalls 3.36 million cars for ignition issues

As a result, GM has raised its recall-related charge for the second quarter by $300 million to $700 million—taking the automaker's total recall-related charges this year to $2 billion.

—By CNBC's Matthew J. Belvedere. Reuters contributed to this report.