Ten years of the diesel scandal: the fraud

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“They're cheating us!” Dr. Axel Friedrich was outraged. The former head of the traffic and noise department at the Federal Environment Agency could hardly contain his anger at the car industry. Friedrich, who holds a doctorate in chemistry, had recognized that the laboratory limit values for the emission standards and the real measured values in European cities did not match. The focus: the diesel engine and its nitrogen oxide emissions. Even if I thought manipulation was possible, I told him, as a journalist, I would need proof of his assertion. Looking back, I know that Friedrich was right. That was in 2012. I would like to report on how I experienced the scandal surrounding defeat devices. When I had my first clues. When I was sure and why it was the USA that provided the decisive impetus.

We humans can smell nitrogen oxides (NOx). These chemical compounds are chlorine-like, pungent, and harmful to health. Diesel engines produce higher levels of NOx than gasoline engines, and the European Union had granted the popular powertrain a rebate: instead of 60 milligrams per kilometer as with petrol engines, diesel engines were allowed 180 mg/km for the Euro 5 standard and 80 mg/km for Euro 6. Mind you, on the test bench. The legal problem was that certain cars were able to recognize the measurement cycle. The control unit for the combustion engine switched to a special characteristic curve that reduced emissions to the permitted level. The experts call this cycle beating, or defeat device. In real operation, everything was different again. Full power without restrictions.

Mobile measuring systems provided the proof

The fact that the immense deviation between laboratory and reality could be proven was due to the development of mobile measuring devices: so-called Portable Emissions Measurement Systems, or PEMS for short, were reduced in size to such an extent that they fit in the trunk and on the trailer coupling of a car. Today, PEMS are a common device for measuring emissions not only in the laboratory but also on the road. Real Driving Emissions (RDE) is the name of this procedure, which is now mandatory.

Yes, there were suspicions, and I was in contact with the (ICCT) in 2014. They had tested 15 vehicles with PEMS and found that the nitrogen oxide limits were exceeded sevenfold on average. It was striking that there were diesel cars that complied with all limits in real operation, while others were more than 24 times (!) above them. Unfortunately, the study was anonymized. The only thing that was clear was that it was technically possible to reduce emissions so that nitrogen oxides on the road were as good as the laboratory values promised. The difference is the money: effective exhaust gas aftertreatment incurs costs, and manufacturers have to generate these from buyers. I published the ICCT's findings in Die Zeit in October 2014—eleven months before the bombshell broke. It's no secret that readers' interest was moderate.

18 billion US dollars

That changed radically on September 18, 2015. The US Environmental Protection Agency (EPA) accused the Volkswagen Group of violating the Clean Air Act with illegal defeat devices. 482,000 vehicles were said to be affected. Even this would probably not have led to a scandal if the EPA had not threatened a fine of 18  billion dollars. A few days later, the Volkswagen Group had to admit that around eleven million cars in Europe had the defeat device. The chairman of the board of management, Martin Winterkorn, resigned.

Loss of credibility and the threat of driving bans

The fact that the diesel engine's market share in Europe has since fallen to 12.4 percent in the first half of 2025 has to do with the subsequent loss of credibility—and driving bans. These driving bans have only been enforced in a few areas. Nevertheless, there are consequences: in the Netherlands, for example, only 100 km/h is permitted on freeways during the day to reduce nitrogen oxide emissions. In Germany, local authorities have worked their way through complicated bans on individual roads. In addition, the measurement procedures for the type approval of a car were tightened considerably after 2015. This in turn has meant that all diesel cars now have a sophisticated SCR catalytic converter to reduce real-world emissions.

First indications, 2007

I have to admit that I always thought Dr. Axel Friedrich's suspicions mentioned at the beginning were plausible. But I couldn't or didn't want to imagine the extent of it. When had I received any clues? In 2011, for example, at a so-called fireside evening in Wolfsburg. Around 20 international trade journalists were invited to a presentation by the head of engine development: Jens Hadler was smart, impressive, and something like the next man at Volkswagen, a mechanical engineer and up-and-comer. He talked about the myriad of global approval standards and how the engines are adapted to them using software. Hadler left Volkswagen in 2012 for unclear reasons. In May 2025, the Braunschweig Regional Court sentenced him to four and a half years in prison without parole. The verdict is not final.

Colleagues also had clues: a former head of department of mine had found an anonymous letter to the editor from 2007 in an archive box. On a squared sheet of paper written on a typewriter, the reader accused Audi AG of cheating on the Euro 4 emissions standard and the six-cylinder engines with displacements of 2.7 and 3 liters with cylinder beating. The head of the department had recognized the potential; however, the detection methods were not yet available at the time. The tipster had not left an address, and publishers were reluctant to spend money on intensive research.

Waiting for the scrapping

The Volkswagen Group has made many people angry. But I don't believe that Volkswagen acted alone. I am convinced that other manufacturers have also manipulated exhaust emissions. Outside Germany, for example. The respective national authorities would have been responsible—and they may have protected industry and jobs in their country more than the air we breathe.

Of the more than 49 million cars in Germany today, around 28 percent have a diesel engine. As a rule, the older the car, the higher the pollutant levels. The newer, the better. At some point, the cars with inadequate exhaust aftertreatment are worn out and go to the scrap press or onto an export ship. This will solve the problem in the foreseeable future, at least for us. I am sure that any other solution would not have been politically feasible.

(mki)