GM chief Mary Barra apologized Tuesday for the US automaker'sfailure to fix defective ignition switches linked to 13 deaths and vowed the companywould "do the right thing."The manufacturer is under fire for not recalling Chevrolet Cobalts, Saturn Ions andother General Motors models over the past decade, despite its own technical evidence that the cars were potentially deadly. GM eventually issued mass recallsthis year.Barra said GM has acknowledged the problem, launched an exhaustive review todetermine what and who is responsible, and pledged top-to-bottom changes inshifting from a "cost culture" to a focus on safety and quality."Today's GM will do the right thing," she told an investigations panel of the HouseEnergy and Commerce Committee in Washington."That begins with my sincere apologies to everyone who has been affected by thisrecall,"sheadded."Iamdeeplysorry."Lawmakers pointed to internal documents showing GM at first refused to change thefaulty switches because doing so would have been too costly and expressedastonishment that the company went ahead with using the parts even though theydid not meet GM standards."That is not something that I find acceptable," Barra said.Heaping pressure on the automaker, weeping relatives marched up Capitol Hill,clutching images of their loved ones, to demand accountability from GM and to tellhow their children died in vehicles they said GM knew were faulty."Our daughters, sons, sisters, brothers, mothers, fathers, wives and husbands aregone because they were a cost of doing business, GM-style," said Laura Christian.Christian's daughter Amber Marie Rose, 16, was killed in 2005 when a Cobalt'sairbags did not deploy in a crash -- possibly due to a faulty ignition.- '$2 too much' -The hearing is the first in what is likely to be a mounting pile of legal troubles forthe US auto giant, including a US Justice Department probe and lawsuits frompeople injured and families of those who died in crashes allegedly tied to theignition issue. Analysts have already speculated that the trouble could cost the company billions ofdollars in penalties and damages, on top of huge costs of the recalls themselves.Lawmakers argued the tragedies could have been avoided if GM acted swiftly to fix aserious but inexpensive problem."Two dollars. That's how little this ignition switch could have cost to repair," saidSenator Ed Markey."But that was apparently $2 too much for General Motors."Also testifying was the acting administrator of the National Highway Traffic SafetyAdministration, the US auto safety agency under attack for not acting on its ownevidence that the ignitions posed dangerous risks to drivers.Several lawmakers said GM and NHTSA repeatedly missed or ignored red flags aboutthe problems."It is important that we get to the bottom of this," said congresswoman MarshaBlackburn. "We want to know who knew what when -- and Ms. Barra that includesyou."- GM pledges transparency -Barra, a lifetime GM employee, said: "More than a decade ago, GM embarked on asmall car program. Sitting here today, I cannot tell you why it took years for a safetydefect to be announced in that program."When we have answers, we will be fully transparent with you, with our regulators and with our customers."GM has hired lawyer Kenneth Feinberg, who handled the September 11 and BP oil spill compensation cases, to study how it should address victims of the accidents."We do understand that we have civic responsibilities as well as legalresponsibilities," Barra said.Legally, GM's 2008-2009 rescue by the government and bankruptcy reorganizationcould protect it from liabilities before that, a scenario that has infuriated somelawmakers.Since February, GM has recalled 2.4 million cars covering model years 2005-2010over the faulty ignitions, which can abruptly switch into "accessory" or "off" positionwhile in drive, especially when the car is jolted. That can turn off the car's electrical systems, including safety airbags, preventingthem from inflating in a collision. GM's documentation shows it was first aware of a problem in 2001 when the carsinvolved were in pre-production.