VW Diesels See Decline in Performance and Fuel Economy When in Emissions Testing Mode

By Paul Riegler on 14 October 2015
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Following the revelation that Volkswagen deceived regulators and customers about the level of emissions coming from its diesel-powered automobiles by installing so-called defeat devices, raises the question of what will happen to the car’s performance and fuel economy once a recall brings the car into full compliance.

Volkswagen is expected to retrofit urea-based emission filtration systems in U.S. diesels, although the head of its U.K. unit said that that will not be the case in Europe.

Although no one outside of Volkswagen knows for sure how to turn on the defeat device, Consumer Reports magazine said it may have found out a way to activate the cheat mode. To accomplish this, using a 2015 Jetta sedan and a 2011 Jetta wagon, reviewers there turned on the hazard lights, pressed the accelerator pedal five times, and then deactivated the rear wheel sensors to make the car believe it’s on a test bench and not in motion.

The 2011 Jetta has only an NOx trap to limit of nitrogen oxides emissions, while the newer model, which has a newer engine, the EA288, has both the NOx trap and Selective catalytic reduction aftertreatment, which uses urea fluid to turn the NOx into nitrogen and carbon dioxide.

The magazine was able to test the change in the cars’ performance and reported in a widely-circulated video that the 2011 Jetta went from zero to 60 mph (96 km/h) in 10.5 seconds with the device activated, an increase of 0.6 seconds over what the car did in normal mode. The activation of the defeat device on the 2015 Jetta did not have a material change in that car’s 0-60 performance, adding only 0.1 second to the 9.1 seconds in normal mode.

Fuel economy dropped from 53 mpg (4.44 l/100 km) to 50 (4.70) on the 2015 model, and the older model saw a decline from 50 mpg (4.70 l/100 km) to 46(5.11) in emissions testing mode.

Consumer Reports did not have a rolling NOx testing device so it was unable to measure changes in emissions.

(Photo: Accura Media Group)