Since early this year, GM has been embroiled in a scandal over why it took more than a decade to begin recalling low-cost Chevrolet Cobalts, Saturn Ions and other cars with the problems that were causing the vehicles to stall during operation. The sources said Manhattan U.S. Attorney Preet Bharara’s office had asked present and former GM employees to come for interviews. In addition to Bharara’s criminal investigation, at least 11 state attorneys general are investigating GM over the ignition-switch problem.