Did Volkswagen’s skirting of the EPA’s diesel emissions rules result in better fuel economy and performance for its cars? According to Consumer Reports testing, it appears so.

Volkswagen has admitted to using special software settings while its diesel cars were being tested for emissions and fuel economy—settings that vanish when the car is driven on the road, resulting in nitrogen oxide emissions up to 40 times the federal standard.

In response to the scandal, Consumer Reports conducted new testing of 2015 and 2011 Volkswagen TDI diesel vehicles in this “cheat” mode to assess fuel economy and performance. We found a noticeable decline in fuel economy for both models. Our testing also showed reduced acceleration with the 2011 model, which is equipped with a lower-tech diesel filtration system.

VW has yet to announce the specifics of the recall to fix its 482,000 diesel-engined Beetle, Golf, Jetta, and Passat models in the U.S. Consumer Reports will conduct another round of testing once the cars have been repaired or updated. Stay tuned for our continued coverage of this issue. 

Volkswagen TDI diesel engine. Consumer Reports tested VW Diesel Fuel Economy