It only announced a recall in February. Nearly two weeks later, it expanded the number of affected vehicles in North America from 780,000 to 1.4 million. It also disclosed additional deaths.
Federal law requires automakers notify a federal safety board within five days of discovering an issue.
GM's new CEO, Mary Barra, recently defended the company's actions in a letter to employees, saying it acted "without hesitation" and "well beyond" recommendations by technical experts. Another company official said GM's review of the issue "was not as robust as it should have been."