Audi voluntarily recalls up to 850,000 diesel vehicles

German luxury carmaker Audi, a Volkswagen subsidiary, issued a voluntary recall of up to 850,000 diesel vehicles Friday, saying it would help reduce engine emissions."Audi aims to maintain the future viability of diesel engines for its customers and to make a contribution towards improving air quality," the Bavaria-based manufacturer said in a statement.Vehicles with affected engines would receive a free software upgrade that "will further improve their emissions in real driving conditions beyon