The National Highway Safety Traffic Administration has launched a probe into why General Motors Co. did not promptly recall more than 1.6 million vehicles after it learned that faulty ignition switches were causing fatal crashes.
The investigation is likely to result in hefty fines for the automaker.
GM recalled the vehicles in two phases this month even though documents filed with the federal safety agency demonstrate that the automaker first learned of the problem in 2004.
Investigators will "determine whether GM properly followed the legal processes and requirements for reporting recalls," the agency said.
The GM recall covers the 2005-2007 Chevrolet Cobalt, 2007 Pontiac G5, 2003-2007 Saturn Ion, 2006-2007 Chevrolet HHR, 2006-2007 Pontiac Solstice and 2007 Saturn Sky vehicles.
GM issued a second apology Thursday and said it will cooperate with the NHTSA.
"We deeply regret the events that led to the recall and this investigation," the automaker said in a statement. "We intend to fully cooperate with NHTSA and we welcome the opportunity to help the agency have a full understanding of the facts. Today's GM is committed to learning from the past while embracing the highest standards now and in the future."
General Motors acknowledged Tuesday that it reacted too slowly to the safety issue, which is linked to 13 deaths.
The ignition switches in the recalled vehicles can be inadvertently turned from the "run" position to the "accessory" position while the car is being driven. When this happens, the engine shuts off and safety systems — including power steering, anti-lock brakes and air bags — are disabled. This has led to at least 31 crashes and the 13 deaths.
NHTSA and GM are urging drivers of the cars to "use only the ignition key with nothing else on the key ring" when operating the vehicle.
According to documents filed with the safety agency, GM knew of the defective ignition switches as early as 2004, and issued a service bulletin for its dealers in 2005. GM encouraged dealers to tell affected customers to remove all unnecessary items from their key chains to prevent the ignition from inadvertently turning off.
The automaker thought that would address the issue because the cars' steering and braking systems remained operational even after the engine was accidentally shut off.
But in 2007 NHTSA brought a report of a fatal crash to GM's attention. In that crash, a 16-year-old Maryland girl was killed after she lost control of her 2005 Chevrolet Cobalt and slammed into a tree. The girl was not wearing a seat belt, and the air bags didn't deploy. Data pulled from the car's black box revealed that the key had been in the accessory mode at the time of the crash, thereby disabling the air bags.
GM then began to track similar crashes, and by the end of 2007 the automaker was aware of 10 such crashes. Black box data were available for nine of those, and the key was found to be in the accessory mode in four of the nine. But the automaker didn't issue its recall until this month.
Ford was the last automaker to be fined for failing to immediately alert regulators of a safety issue, paying $17.4 million for delaying the recall of Escape sport utilities with gas pedals that could become stuck.
In 2009 and 2010, NHTSA fined Toyota Motor Corp. more than $65 million for violations of federal vehicle safety laws and for not recalling cars quickly in response to complaints about sudden acceleration.