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.
Read MoreWe're done with recall-based dismissals: GM CEO