Since February, when GM began recalling Chevrolet Cobalts and Pontiac G5s after it determined faulty ignition switches had led to the deaths of at least 13 people, Barra has repeatedly said they are committed to changing the culture at the company.
"I want this terrible experience permanently etched in our collective memories," Barra told the House Energy and Commerce Subcommittee on Oversight and Investigations at a hearing Wednesday. "This isn't just another business challenge: This is a tragic problem that never should have happened and it must never happen again."
Barra said 15 people have been fired for repeatedly failing to report known safety problems and a "Speak Up for Safety" initiative has been launched to give employees a space to express concerns. She also said GM appointed 40 new defect investigators -- most who were already GM employees -- to investigate safety problems.
Members of the committee were unimpressed by the changes GM has taken so far. Committee Chairman Tim Murphy, R-Pa., slammed the firings as insignificant, wondering how it was possible to create company-wide changes with so few changes.
"If you haven't changed the people how do you change the culture?" he said.
"I would suggest you bring in some outside, fresh blood, " added Rep. G.K. Butterfield, D-N.C.
They were similarly incredulous over the results of an internal investigation, led by former U.S. Attorney Anton Valukas, which found no evidence of a cover-up or conspiracy.
"That report should be subtitled 'don't assume malfeasance when incompetence will do,'" Murphy said. "We want to know from Ms. Barra, not just how it happened, but why."
Ranking member Diana DeGette, D-Colo., said it was "frankly alarming" that none of GM's top executives had been made aware of a switch that had been discovered and repeatedly dismissed for more than a decade.
It "smacks of a big cover-up to me," said Rep. Phil Gingrey, R-Ga. "How could they not know?"
Valukas said he had "unfettered" access to GM's records and employees in the investigation, but only limited access to records at Delphi, a company that manufactures a number of parts for GM, including the switches, and no access to its employees.
Last month, the U.S. fined GM $35 million for its botched handling of the recall.
The switches involved were found to turn too easily, and would be accidentally knocked into "accessory mode," shutting off power steering and causing airbags to fail to deploy in the event of a crash.
GM has linked the switches to the deaths of 13 people, but other reports speculate the number may actually be 74, as GM's count only includes head-on collisions, not side collisions that lead to fatalities when airbags failed to deploy.
2014: The Year in Music [PHOTOS]