from The Washington Post

The tech behind how Volkswagen tricked emissions tests

By Andrea Peterson and Brian Fung

(Odd Andersen/AFP/Getty Images)

Volkswagen isn’t hiding from its emissions cheating scandal, which the company now says affects some 11 million diesel cars worldwide.

“Let’s be clear about this: Our company was dishonest with the EPA and the California Air Resources Board and with all of you,” Volkswagen U.S. chief Michael Horn said Monday night. “In my German words, we have totally screwed up.”

Thanks for finally coming clean, VW. But how exactly did the technology behind Volkswagen’s so-called defeat device actually work?

Regulators allege that Volkswagen installed software into its cars that allowed the autos to circumvent EPA tests. But that still doesn’t explain how VW vehicles were able to determine when they were being subjected to an emissions test in the first place.

To understand more about how Volkswagen cheated, we have to know a bit about the EPA’s testing process. When carmakers test their vehicles against EPA standards, they place a car on rollers and then perform a series of specific maneuvers prescribed by federal regulations. Among the most common tests for passenger cars is the Urban Dynamometer Driving Schedule (UDDS), which simulates 7.5 miles of urban driving. Here’s what that looks like, expressed as a speed profile.

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