Road & Track just unearthed some important information on the cheat device used by Volkswagen for their 2.0-litre turbodiesel engine.
In 1999, Audi was hard at work developing their 3.0-litre TDI powerplant. Everything was going smoothly, but it clattered too much when it was cold. Since they wanted to use these engines in luxury vehicles, they had to find a way to limit that noise, otherwise customers would choose something with a more refined sound.
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The solution was to inject more fuel into the cylinders when it is started. This invention, dubbed Pilot Injection, reduce valve clattering, but drastically increased emissions.
This is how Audi came with the Acoustic Function system (ironically, this is the name that investigators found early into their research, which led them to believe it was a code name). It's a little software that can detect if the car is being emissions-tested and deactivates Pilot Injection as needed.
In 2006, Volkswagen was trying to make their 2.0 TDI EA189 engine emissions-compliant. They could have injected urea in the system, but it would have meant licensing the technology from Mercedes-Benz... Then, an engineer had the idea to use the Acoustic Function, and the decision was approved by VW's direction.
And the rest, as they say, is history...