The software used by Volkswagen to get around environmental standards in some 11 million vehicles effectively told each car to go into a "clean mode" when it detected the car was being tested for emissions.
Details about how the automaker was able to elude emissions testing -- the "defeat device," as the software has been called -- is included in a Sept. 18 letter from the Environment Protection Agency (EPA) to Volkswagen.
That letter prompted VW to admit that half a million Volkswagens and Audis in the U.S. -- and 20 times that number of vehicles worldwide -- were actually polluting 10 to 40 times more than government agencies thought.
Volkswagen AG CEO Martin Winterkorn stepped down Wednesday in the wake of the scandal, which has cost the company billions in lost value as its stock price has plunged. Winterkorn stated that he was "shocked" and "not aware of any wrongdoing" on his part.
One expert believes a software development audit trail is likely to uncover who knew what and when.
How Volkwagen fooled EPA emissions tests
According to the EPA's violation letter to Volkswagen, dated Sept. 18, several models of Volkswagen vehicles built between 2009 and 2015 and Audi A3 models from 2010 to 2015 had software installed in the vehicles electronic control module that could sense when an emissions test being conducted.
According to the EPA, "the position of the steering wheel, vehicle speed, the duration of the engine's operation, and barometric pressure" -- all very specific indicators of an emissions test -- acted as the activation switch for the "defeat device." Essentially, the vehicles' electronic control module (ECM) was set to "clean" mode for the remainder of the emission's test procedure.
"The 'switch' was activated and the vehicle ECM software ran a separate 'road calibration' that reduced the effectiveness of the emission control system (specifically the selective catalytic reduction or the lean NOx trap," the EPA said.
Kirk Wennerstrom, marketing director of the Greenwich Concours d'Elegance, a vintage and classic car show in Greenwich, Conn., explained what VW did with its embedded software was akin to "a sports jock hiring a gangly nerd just to pass SATs."
Wennerstrom, an aficionado of car technology whose family started the Greenwich car show in 1996, said EPA emissions tests are stringent and cover a wide, varying range of vehicle speeds, hot and cold stops and starts, so "there's not much wiggle room."
Around 2009, the National Low Emission Vehicle program set in place more strict requirements on NOx emissions.
To meet the new standards, diesel manufacturers inject a special urea fluid known as AdBlue in the exhaust stream that catalyzes the nitrogen oxide or NOx fumes. While the fluid injection system worked to reduce NOx emissions, it also added weight and cost, and drives up the ownership cost as drivers have to keep refilling the fluid.
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