WASHINGTON — Mary T. Barra, chief executive of General Motors, walked into a crowded House hearing on Wednesday with her high-powered lawyer at her side, confident that his exhaustive internal investigation about a deadly defect would convince lawmakers that G.M. is taking safety seriously.

But instead Ms. Barra came under attack again for G.M.’s long failure to recall defective small cars, and now faces further investigations into its safety issues, including a revelation that an employee experienced stalling problems in 2005 in a Chevrolet Impala that was not recalled until this week.

The hearing was an opportunity for G.M. to rebuild credibility with lawmakers, as well as the family members of crash victims who packed the room, after admitting in February that it failed for more than a decade to recall millions of defective cars tied to at least 13 deaths and 54 accidents.

Yet the nearly three hours of testimony by Ms. Barra and G.M.’s outside lawyer, Anton Valukas, left lawmakers more frustrated and skeptical about the nation’s biggest carmaker’s commitment to safety.