Fiat Chrysler Automobiles NV shares were halted after plunging the most intraday on record as the U.S. government accused the company of using software that allowed excess diesel emissions in about 104,000 vehicles. The Environmental Protection Agency alleges Fiat Chrysler violated the Clean Air Act by installing and failing to disclose the software in Jeep Grand Cherokee sport utility vehicles and Ram 1500 pickups sold in the U.S., according to a statement.