Automaker concludes internal investigation of fatal ignition switch problem . The National Highway Traffic Safety Administration is investigating the cause and effect behind a defect that could lead to cars stalling in cold weather. Some in GM knew for years there was a problem , but only started big recall this year .
Automaker concludes internal investigation of fatal ignition switch problem . But House and Senate committees continue to probe the matter , promising hearings . Some in GM knew for years there was a problem , but only started big recall this year .