Consumer Reports recently did a test.
They wanted to figure out how much power and fuel economy VW TDI’s gained through their emission defeat device. To do this, they tested two VW TDIs: one in ‘normal mode’, and one with the emissions cheat activated. In order to get the cars to enter cheat mode while on the road, they disconnected the rear wheel sensors to make the cars think they’re on a dynometer. The results were significant: VW TDIs during normal mode had better acceleration and fuel economy. While VW is quickly working on a solution to bring all affected vehicles into compliance, it’s clear that doing so will both make the cars slower and less efficient.