Today GM announced that it will introduce changes to the Chevrolet Volt to guard against fires like the ones that occurred after crash tests last year.

New Volts will incorporate the changes, including steel reinforcements, starting this month. The approximately 12,000 cars that have already been built (about 8,000 have been sold so far) can also be retrofitted at dealerships starting in February. The retrofits will be part of a voluntary program, not an official product recall.

GM has also confirmed what caused a handful of Volt battery fires in testing last year. A side-impact test caused part of the Volt's structure to break into the battery casing, and a small coolant leak was exacerbated when, as part of the test procedure, the battery was slowly turned over. When the battery pack was upside down, the coolant leaked onto a circuit board, which caused a short, and then the fully charged battery caught fire.