With most of the 2.6 million Chevrolet Cobalts and other small cars recalled by General Motors still awaiting repairs, U.S. lawmakers said they remain concerned customers are learning too little, too late about a defective ignition switch linked to 13 deaths, including one in Canada.

In their first crack at GM since the automaker’s hand-picked independent investigator released a damning report of the company’s handling of the defect, congressional committee members continued Wednesday to express disbelief that senior executives were kept in the dark.

“I remain unconvinced there wasn’t an effort to ‘cover up’ bad decisions to avoid liability,” said U.S. Rep. Tim Murphy (R., Pa.), chairman of a House subcommittee investigating why GM waited a decade to recall cars with a deadly safety defect involving Chevrolet Cobalts, Saturn Ions and other compact cars.

They also questioned whether GM’s chief executive officer Mary Barra is too much of a company insider to bring about real change. An engineer, Barra is a second generation GM employee.

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While apologizing for the company’s mishandling of the issue and vowing it would not happen again, Barra also said: “The story of the Cobalt is a story of individual and organization failures that led to devastating consequences.

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

Murphy also expressed disbelief that not a single GM whistleblower had come forward in 10 years despite complaints from customers, inquiries from federal safety regulators and lawsuits against the company, to alert senior executives to the ignition switch hazard.

Congresswoman Jan Schakowsky (D-Ill.) said she found it hard to believe a single engineer acted alone, referring to Ray Di Giorgio, the GM engineer who originally approved the use of a switch that didn’t meet the company’s specifications.

GM finally recalled the Cobalt, Saturn Ion and other small cars in February 2014, saying they had a faulty ignition switch that can shift out of the run position, into accessory or off, cutting power to the engine, brakes and steering wheel and also deactivating the airbags.

The automaker has said the defect may be linked to 13 fatalities and 31 other crashes.

Appearing before the committee for the first time since issue his report, Valukas defended it against accusations leveled by Clarence Ditlow, executive director of the Center for Auto Safety, a U.S. advocacy organization, that it’s a “whitewash” aimed at helping GM avoid criminal prosecution by exonerating the most senior officials.

Valukas said he was asked to find out what happened and why, not to decide who should be held responsible. “The (GM) board (of directors) was charged with determining whether the employees at the top level lived up to their responsibilities,” Valukas said.

Valukas’ damning report, released two weeks ago, described a culture of incompetence and neglect. It referred to the “GM nod” and the “GM salute” — gestures employees used to shift blame and shirk responsibility for fixing the problem.

But Valukas denied GM engaged in a cover-up. A large number of people had information they didn’t believe was safety related, he said. “We did not find evidence that any individual deliberately withheld information from someone else.”

Since the report’s release, Barra said GM has fired 15 individuals, including Ray Di Giorgio, the engineer responsible for approving the switch in 2002, and restructured the safety decision-making process to ensure senior executives are kept in the loop. “We are leaving no stone unturned,” she told the committee.

Di Giorgio was also blamed for choosing to upgrade the part in 2006 without changing the part number, a decision that left no paper trail identifying the problem or what was done to fix it.

As proof GM’s corporate culture has changed, Barra said she has initiated a “very aggressive” recall program involving 20 million vehicles worldwide, a Speak Up for Safety program that encourages employees to raise concerns, and appointed 35 to 40 internal safety investigators.

GM has already been fined the maximum $35 million (U.S.) penalty that can be levied by the National Highway Traffic Safety Administration for failing to disclose the defect in a timely manner.

That’s a drop in the bucket for a company that made $4 billion (U.S.) in profit last year, one congressman noted.

A far bigger concern is a possible criminal prosecution that in a similar case against Toyota Motor Corp. led the Japanese automaker to pay $1.2 billion (U.S.) to settle with the U.S. Justice Department earlier this year.

GM has also faced accusations it deliberately covered up the defect in the years leading up to its filing for bankruptcy protection and subsequent government bailout, fearing a massive recall could jeopardize its survival.

The company has denied that’s the case.

GM has been given until Oct. 4 by federal highway safety regulators to complete the recall, a deadline Barra said she expects to meet. The company has so far fixed 200,000 vehicles.

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In the meantime, vehicle owners are being told the cars are safe to drive if they remove everything but the car key from their key chains. Heavy or dangling key chains are more prone to being knocked out of position.

Murphy said GM isn’t communicating on its website that failure to do so is a serious safety hazard. Barra said she would look into making that clearer.

Barra also said what she sees on people’s key chains has amazed her and that it’s become an issue the whole industry needs to address.

The subcommittee released a chain of internal emails that showed GM employee Laura Andres had warned other company engineers in August, 2005, that it may have a “serious safety problem” on its hands.

Andres wrote the email after the 2006 Chevrolet Impala she was driving in August 2005 shut off when she drove over a bump in the road. She said the shutoff appeared to be linked to the design of the Impala’s ignition switch, a vehicle that shared many components with other small cars, including the Cobalt.

“I was driving 45 mph when I hit the pothole and the car shut off, and I had a car driving behind me that swerved around me. I don’t like to imagine a customer driving their kids in the back seat, on I-75, and hitting a pothole, in rush hour traffic,” Andres wrote, saying it could lead to a “big recall.”

Andres urged that engineers “seriously consider changing this part.”

At the time, GM officials publicly described the problem as a “customer convenience” issue, Valukas said in his testimony before the committee.

In fact, the part was replaced in 2006 but not given a new part number, a fact that didn’t come to light until 2013 during a lawsuit launched by the family of Georgia nurse Brooke Melton.

Both Barra and Valukas said part of the problem was GM engineers didn’t believe the ignition switch posed a safety risk.

GM officials publicly stated between 2005 and 2009 that problems with vehicles stalling were a “customer convenience” issue, Valukas said.

Some committee members accused GM of deliberately covering up the mistake in a bid to avoid lawsuits in the years leading up to its 2009 bankruptcy filing. The automaker is in court fighting to limit any claims against it to those that occurred after its emergence from bankruptcy protection.

Valukas, who said his access to GM parts supplier Delphi has been limited, said he would continue to disclose any new information he received, including from lawyers representing plaintiffs who have sued GM over the defect.

The three-hour hearing was witnessed by many families of the victims, whose photos lined the back wall.

Valukas said several hundred people worked on his investigation. Computers were used to narrow down 41 million documents to the most relevant ones.

GM’s problems have led U.S. highway safety regulators to broaden their investigation into air bag and ignition switch problems across the auto industry.

On Wednesday, the safety regulators said they were looking into whether the keys in certain Chrysler minivans and SUVs can fall out of the run position under “harsh roadway conditions.”

GM shares have held up despite the publicity surrounding the recalls. They have gained 2.2 per cent from Feb. 12, the day before the first ignition recall was announced, through Tuesday.