DETROIT — The U.S. government’s highway safety agency is expanding three investigations for brake and air bag troubles that could affect more than 2.3 million vehicles from Ford, Volkswagen and Nissan. The expansions by the National Highway Traffic Safety Administration were announced Monday and over the weekend on the agency’s website after investigators found more consumer complaints about the problems: • Ford Fusion, Mercury Milan, Lincoln MKZ: NHTSA has expanded a 2016 investigation to include just over 1 million vehicles.