After a year-long investigation, a team of researchers from the University of California, San Diego (UCSD) and Ruhr-University Bochum in Germany has uncovered the code used by Volkswagen to cheat diesel emissions tests. The announcement coincides with preliminary investigations by the Stuttgart public prosecutor's office into alleged "fraud and criminal advertising" in diesel cars at Mercedes.

News of the emissions cheating scandal, known colloquially as Dieselgate, broke in September 2015 after an independent investigation revealed Volkswagen diesel cars returned unusually high nitrogen oxide (NOx) emissions in real-world testing. The company subsequently admitted some of its diesel cars were fitted with a simple "defeat device" that made the engine return better emissions figures under test conditions.

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Since then, the company has started buying cars back in the US and proposed a simple fix for cars elsewhere in the world, but exactly what the "defeat device" behind the cheat looked like had remained a mystery. But computer scientists have trawled through copies of the base code of VW onboard computers to provide answers.

According to the team, a specific piece of code masquerading as a way to control the engine sound was responsible for activating the "defeat device." The code kept an eye on a number of conditions, such as distance, speed and position of the wheel, and when they aligned with those produced when the car was being tested, the onboard computer would switch the engine into regulation-skirting low NOx mode. This technique was effective because the conditions of the emissions tests are standardized with details available to the public.

The team says a similar code was discovered on the Fiat 500X during testing, but it employed a simpler approach. The emissions-curbing system would run for 26 minutes and 40 seconds after the engine was turned on, which would cover the length of most emissions tests.

Mercedes to join the club?

When we first wrote about the "defeat device" in September 2015, the question of whether Volkswagen was the only company to cheat emissions testing came up. Although VW has taken a big hit as a result, allegations leveled at other auto manufacturers are yet to make the same splash.

That could change with today's news out of Germany. The Stuttgart public prosecutor has raided a number of Daimler AG offices "due to suspicion of fraud and criminal advertising relating to the possible manipulation of exhaust-gas aftertreatment in passenger cars with diesel engines."

Although the allegations are different to those leveled at VW – aftertreatment is used to catch harmful particulate emissions before they leave the tailpipe of a diesel car – they have the potential to cause a similar stir as the initial Dieselgate scandal if proven to be true.

Daimler AG has said it is cooperating with authorities, but can't comment further at this time.

The paper detailing the code employed by Volkswagen can be viewed here (PDF).

Source: UC San Diego, Daimler AG