Tom Krisher and Dee-Ann Durbin

U.S. Rep Diana DeGette wants to know why General Motors did not act sooner to address a potentially deadly defect that it knew about for at least a decade.

DeGette said Friday she is leading a congressional investigation to learn more about when GM knew about the ignition switch failure and “why they didn’t inform the public.” GM last month recalled 1.6 million Cobalts and other compact cars. The switch can slip out of the “run” position, causing the engine to shut off.

DeGette says GM has linked the problem to at least 12 deaths and 31 crashes.

DeGette says she will also press officials from the National Highway Transportation Safety Administration about why they never ordered GM to recall the cars. The congressional hearings will start Tuesday.