Congressional investigators looking into why General Motors Co. took nearly a decade to recall vehicles with faulty ignition switches said Sunday that federal regulators twice declined to open formal probes into complaints about the cars and that GM rejected a proposed fix for the problem in 2005 because it would have taken too long and cost too much.

The findings by staff for the Republican majority of the House Energy and Commerce Committee offer new details about events leading up to GM's recall of 2.6 million vehicles...