While VW's diesel emissions scandal might seem like an easy explanation for losing the top ranking, remember that the EPA's violation notice only came on September 18. With just a few days left in the month when things really started heating up, the problem likely had no effect on this ranking. Instead, falling demand in China likely played a more significant part, according to Bloomberg.
Even if the cheating software doesn't affect the rankings through Q3, the fallout from the scandal and the stop sales on popular models in major markets makes VW retaking the top in the fourth quarter look nearly impossible.
When the final numbers came in for 2014, Toyota won the delivery battle for the year with a volume of 10.23 million vehicles, and VW was just off that pace at 10.14 million. At the time, a still-booming Chinese market was predicted to possibly to give Germans the edge in 2015. However, that hasn't happened after a slump hit the auto industry there for several months earlier this year.