Consumer Reports was able to find out, tapping into what it believes is the cheat mode. By turning the car to accessory mode, flipping on the hazards, and tapping the gas pedal five times, CR was able to defeat the auto-engaged traction and stability controls, which it believes activates cheat mode. The safeties will reengage if it detects the rear wheels spinning, so the next step was what CR called "a hack." The team unplugged the rear wheel sensors, so the car's computers couldn't tell whether the wheels were spinning. By the way, don't try this at home.
With that done, CR hit the road, testing both a 2011 Jetta Sportwagen TDI and a 2015 Jetta TDI sedan in their normal and cheat modes. Why both cars? Well, the 2011 uses the EA188 diesel, which represents the bulk of the affected cars, while the newer Jetta uses the latest EA288, which just arrived for model year 2015. The results are, in a word, interesting.
The EA188 engine lost 0.6 seconds on the way to 60 miles per hour while in emissions-compliant cheat mode, and fuel economy fell from 50 miles per gallon to 46. For the newer EA288, the 0-60 difference was negligible – just a tenth of a second – while the fuel economy dipped from 53 to 50 mpg.
There are a few takeaways here. First of all, and as suspected, running in cheat mode did hurt both performance and fuel economy. But perhaps more importantly, even in emissions-compliant mode, both vehicles easily beat their EPA fuel economy estimates. According to FuelEconomy.gov, the highest rated 2011 TDI Sportwagen, the manual-trans model, was rated at 30 mpg city and 42 mpg highway, with a combined rating of 34 (the auto drops the city and combined ratings by one mpg, while the highway falls by three). The best a 2015 Jetta TDI sedan can do according to Uncle Sam, meanwhile, is 31 city, 46 highway, and 36 combined with the manual (again, the auto is worse, but only by a single highway mpg).