The government's investigation of post-crash fires in Chevrolet Volt batteries closed Friday after further testing proved the changes General Motors has implemented better protect the batteries.
The National Highway Traffic Safety Administration posted the results of its defect probe late Friday, saying the investigation, which opened Nov. 25, is over and the voluntary measures GM has taken are sufficient.
GM announced Jan. 5 it would retrofit 14,735 Volts already built and make permanent changes on the assembly line at the Detroit-Hamtramck plant where the Volt is made. The plant is still on holiday shutdown, but will resume production Feb. 1, said GM spokesman Greg Martin.
"The agency's investigation has concluded that no discernible defect trend exists and that the vehicle modifications recently developed by GM reduce the potential for battery intrusion resulting from side impacts," NHTSA said in a statement. "Based on the available data, NHTSA does not believe that Chevy Volts or other electric vehicles pose a greater risk of fire than gasoline-powered vehicles."
"When there is new technology in the mainstream, people are not familiar with it," said analyst Aaron Bragman of IHS Automotive in Northville. "There will be more teething pains with electric vehicles but Volt owners are the happiest in the land."
NHTSA released an analysis of its battery testing, fire incident reports, a video of a battery fire and guidance for emergency responders, tow truck operators and vehicle storage facilities.
Those people are instructed to look for signs of battery fires at the accident scene and be aware of the potential for fire days later.
No Volts on the road have caught fire. There are more than 200,000 fires each year that start in gasoline-engine cars.
NHTSA also warns anyone dealing with electric vehicles to assume the batteries are energized and fully charged.
"NHTSA's decision to close their investigation is consistent with the results of our internal testing," said GM's Martin. "The engineering enhancements that GM announced Jan. 5, 2012, will provide additional protection for the battery minimizing the risk of a post-crash fire."
The modifications include extra steel around the battery pack to prevent puncture. Leaking coolant contributed to electrical fires in two Volt batteries more than a week after crash tests.
GM added a sensor to monitor coolant levels and software to detect when coolant levels drop.
A Dec. 22 government crash test -- after car modifications -- did not cause intrusion into the battery case and the coolant did not leak.
But NHTSA itself is under fire. A U.S. House of Representatives subcommittee will hold a hearing Wednesday in Washington to ask what the agency knew about Volt fires and when it knew it.
Republican congressmen have asked why the agency did not warn the public immediately after the first fire in June.
GM sold 7,671 Volts in 2011, including 1,529 in December.
About 250 Volt owners requested a loaner vehicle or said they wanted to sell their Volt back to GM, Martin said.
