U.S. opening formal probe into GM Volt fire risk Photo 5:46pm EST (Reuters) - U.S. auto safety regulators are opening a formal investigation into fire risks in General Motors' Volt vehicles. The National Highway Traffic Safety Administration said on Friday it was taking the step after efforts to recreate a May crash test saw fires result from two out of three crash tests performed this month. "While it is too soon to tell whether the investigation will lead to a recall of any vehicles or parts, if NHTSA identifies an unreasonable risk to safety, the agency will take immediate action...