The Detroit automaker said it reinforced the structure around the Volt's battery pack to spread the force of impact in severe side-door collisions and added a new sensor to monitor coolant levels around the battery.
"We want to provide that peace of mind for our customers, that even in a severe side crash, their vehicles will not have an issue," said Mary Barra, GM's senior vice president for global product development.
Tests conducted by the National Highway Traffic Safety Administration last May concluded that damage to the electric vehicle's lithium-ion batteries during crashes could lead to post-crash fires, sometimes even weeks after accidents.
Those fires would not ever likely put drivers in danger of fire, but could pose a danger to repair shops unfamiliar with proper safety procedure, dealing with the car after accidents.
NHTSA, which formally launched an investigation on Nov. 25, said in a written release that it is "continuing to gather and assess information" on the post-crash fire risks in the Volt. Mark Reuss, GM's North American president, said he's hopefully the series of structural changes would result in a "positive outcome."
In more than 1 million miles of testing and 20 million miles driven by customers, Barra said no incident had replicated the government tests. But in examining the federal findings, GM found found a ruptured battery saturated in coolant could provide electrical conductivity that, in theory, could spark a fire.
Reuss said General Motors was not recalling the approximately 8,000 Volts in service, but car owners could voluntarily request the alterations, which add between 2 and 3 pounds to the weight of the car. Dealerships should have necessary parts in stock by February.
New units produced at the company's Hamtramck, MI assembly plant will automatically have the safety measures installed. Production was not disrupted during the revamping. GM declined to disclose how much the customer satisfaction program and redevelopment of the vehicle's structure would cost.
Best sales month in December
Despite the investigation, the Volt enjoyed its best sales month ever in December. The company reported Thursday it sold 1,529 units. That gave the automaker a final tally of 7,671 units sold in 2011, below the company's official goal of 10,000.
Indeed, the Volt is arguably GM's, and certainly Chevrolet's. most important image or "halo" vehicle this year. The company has had a stated goal of selling 60,000 Volts this year, but that number is in serious jeopardy if the public doesn't think they are safe.
The car is powered by lithium-ion batteries, which allow a driver to go about 35-40 miles on a charge. When the battery runs out, a gasoline-powered motor kicks on to power the battery, so that there is never any fear on the part of the driver that they will be stuck without a dead battery.
GM was the first to launch such a vehicle, which can be a boon to people driving fewer than fifty-miles a day. Toyota, Ford and the upstart Fisker Automotive are also launching similarly powered vehicles that combine pure electric operation backed up by a gasoline motor.