Both companies have a multitude of issues.
Toyota's four-year reign as the number one global automaker may be coming to a close. The Japanese company is suffering production delays due to Japan's most devastating earthquakes since 2011. Toyota deliveries have dropped 2.3% to 2.46 million vehicles between January and March. Meanwhile, despite dealing with the Dieselgate scandal, VW deliveries have actually increased by .8% to 2.5 million vehicles. VW's reputation has been damaged in the US, but this has been offset by strong sales in China and solid sales in Europe.
Steel shortages were already causing delays for Toyota when the earthquakes hit. Toyota manufactures 40% of its global vehicles in Japan, so the earthquakes have greatly affected sales. General Motors has maintained the third overall sales spot with 2.36 million deliveries. Volkswagen has certainly weathered the storm here, and has impressively come back on top (for now).