Stricter capex will help drive an improvement in returns and accordingly, Diess said that VW operating margins are forecast to rise from the current level of 2% to around 4% by the year 2020. The margin will rise to 6% by the year 2025, the executive added. Volkswagen topped the league table of German auto manufacturers for third quarter results this year, when it reported 4.4% growth in sales volumes and beat the consensus for profit-before-tax by 19%. But the industry titan has seen its market share crimped throughout Europe, its largest market, during 2016 as buyers shun the core Volkswagen brand following the emissions rigging scandal. It also faces a resurgent threat from U.S. regulators after it was reported in November that authorities are now investigating the group's Audi brand over a separate emissions cheating device, initially discovered by the California Air Resources Board. Volkswagen hasn't officially commented on the press reports.