General Motors Co. plans on Thursday to release the findings of a much-anticipated investigation into why it delayed recalling defective cars linked to at least 13 deaths.

Chief Executive Mary Barra hired former U.S. Attorney Anton Valukas to conduct the internal probe and promised regulators and Congress an unflinching and public accounting of the automaker’s safety failings.

The report is expected to detail why GM took a decade to recall about 2.6 million vehicles with a faulty ignition switch that shut off cars and their critical safety systems.

The automaker hired Valukas to investigate whether GM balked at fixing the cars because of the expense, and whether employees covered up the problem or hid key details from the National Highway Traffic Safety Administration.

The report is also expected to pinpoint when Barra herself learned of the problem. A longtime GM executive, Barra took the helm of the company in January. Barra has said she first heard about the switch issue late last year.

GM’s internal inquiry seeks to get ahead of ongoing investigations by NHTSA, the Department of Justice and Congress into the ignition switch problem.

The report represents “progress, but not quite closure,” said Christian Mayes, an auto industry analyst at Edward Jones.

GM still has to deal with the government investigations, product-liability lawsuits and the question of how to compensate crash victims or their families, Mayes said.

Still, the GM report could be an important step in restoring the company’s credibility and integrity, he said.

“This voluntary investigation bought them time in having to answer detailed questions up to this point,” Mayes said. “They could say we have this investigation underway. But now there should be details that shed light on what happened.”

Much of the report is expected to deal with the nuts and bolts of GM’s engineering and recall processes, said Alan Baum, an auto industry consultant.

“GM will say it has learned from this, and that it is already implementing the recommendations,” Baum said.

Auto safety advocates will be looking for details about why the faulty switch was approved by GM’s engineering staff for small cars such as the Chevrolet Cobalt and Saturn Ion. GM no longer builds the models with the switch problem.

Drivers were killed or injured in the cars because the switch can suddenly cut off in certain conditions, such as driving on rough roads or when the driver has an especially heavy key ring. GM has warned drivers to operate the vehicles with only a single key until they are repaired.

So far, GM has repaired fewer than 100,000 of the millions of vehicles recalled because of the defective switch and said it could take at least until October to fix all the cars.

In 2001, GM engineers had two competing designs for the switch, said Clarence Ditlow, executive director for the Center for Auto Safety.

“GM approved and put into production a less safe and cheaper part,” Ditlow said. “Valukas has to explain that.”

The automaker should have chosen the other proposed system, which had a longer and stronger spring that required greater force to start and turn off the vehicles, Ditlow said.