Danny Hakim, Aaron M. Kessler, and Jack Ewing writing about the VW scandal for The New York Times:
Confronted again, Volkswagen continued to maintain that there was a problem with the testers, not the vehicles.
California regulators changed tack, examining the company’s software. Modern automobiles operate using millions of lines of computer code. One day last summer, the regulators made a startling discovery: A subroutine, or parallel set of instructions, was secretly being sent by the computer to what seemed to be the emissions controls.
Regulators were floored. Could Volkswagen be trying something similar to what the heavy-truck industry did to manipulate emissions tests in the 1990s?
Regulators set out to cheat the cheat, tweaking lab test parameters to trick the car into thinking it was on the road. The Volkswagens began spewing nitrogen oxide far above the legal limit.
Crazy. (Emphasis mine.)