Federal regulators decided not to open an inquiry on the ignitions of Chevrolet Cobalts and other cars even after their own investigators reported in 2007 that they knew of four fatal crashes, 29 complaints and 14 other reports that showed the problem disabled air bags, according to a memo released by a House subcommittee on Sunday.

Then in 2010, the safety agency came to the same decision after receiving more reports that air bags were not deploying…

The striking new details in the memo bolster the contention that both G.M. and the National Highway Traffic Safety Administration, more than previously acknowledged, ignored or dismissed warnings for more than a decade about a faulty ignition switch that, if bumped, could turn off, shutting the engine and disabling the air bags. General Motors has recalled nearly 2.6 million cars and has linked 13 deaths to the defect.