General Motors declined to disclose how many Cobalts had been bought back under lemon laws, saying, “It is very difficult to answer questions about claims that may be more than a decade old.” That makes it impossible to calculate a precise nationwide total because reporting and disclosure rules differ from state to state, and federal regulators do not compile such data.

But in Florida, a state that collects data on repurchased lemons and some other buybacks, the Cobalt was the most-repurchased car in its class manufactured in 2005, its first model year. And in May 2005, G.M. was so alarmed by the early number of buybacks, according to a G.M. filing with federal regulators, that the automaker’s brand quality division urged its engineers to reopen an investigation into the car’s faulty ignition switch, which was one source of buyback complaints.

“It’s a vehicle with a poor track record, with deep concerns about its safety and performance,” said Rick Soletski, executive director of the International Association of Lemon Law Administrators, a group of American and Canadian officials that acts as an advocate for lemon programs.

The flawed switch, and G.M.'s failure to correct it for more than a decade, will be the focus of a congressional hearing on Tuesday, when Mary T. Barra, the G.M. chief, and David J. Friedman, acting head of the National Highway Traffic Safety Administration, are scheduled to testify.

The automaker has linked 13 deaths to the defect in Cobalts and several other models. In her prepared remarks, filed with House investigators on Monday, Ms. Barra said, “I cannot tell you why it took years for a safety defect to be announced.”