How ICCT research unearthed
the Dieselgate scandal
One decade ago, ICCT research uncovered shocking discrepancies in laboratory and on-road emissions if diesel cars, leading to the exposure of the Volkswagen emissions scandal—a pivotal moment for the automotive industry that continues to influence policy today.
In the 1990s, diesel cars became increasingly popular in Europe, promoted as a cleaner and more efficient alternative to gasoline-powered engines. By 2011, more than half of newly registered cars ran on diesel, but emissions from these vehicles were linked to serious public health risks, including respiratory illnesses and premature deaths.
In 2013, ICCT researchers tested diesel cars under real-world conditions and found that Volkswagen, Europe’s largest automaker, sold diesel vehicles emitting nitrogen oxides (NOx) at levels between 5 and 35 times higher than regulatory limits. Sharing our findings with regulators prompted investigations that confirmed discrepancies between laboratory tests and real-world performance. Subsequent research revealed that this issue affected multiple manufacturers and markets worldwide.
Reshaping vehicle regulation worldwide
The Volkswagen emissions scandal, or “Dieselgate,” revealed systemic issues and had a lasting impact on vehicle regulations across the globe: today, governments in Europe, China, India, South Korea, and the United States conduct real-driving emissions testing to ensure that vehicles meet standards throughout their lifetime, helping protect both public health and the environment. In Europe and the United States, increasingly progressive emission standards are accelerating the transition to electric vehicles . Through international pledges like the Zero Emission Vehicles Declaration, U.S. states as well as countries in the EU have committed to phasing out the sale of these dirty cars. This shift toward cleaner vehicle technologies is mirrored by rapid electrification in other major and emerging markets around the world.
Despite this progress, millions of high-emitting diesel vehicles remain on roads worldwide, exacerbating air pollution and harming public health. In Europe, for example, roughly 53 million diesel cars were sold between 2009 and 2019—many emitting nitrogen oxides well above legal limits. In 2025, ICCT estimates that a large majority of these vehicles are still driven today, with 16 million vehicles showing suspicious levels of emissions currently in use—of these, 11 million vehicles show extreme levels of emissions. This issue is prevalent across manufacturers.
The scandal explained
The year 2025 marks ten years since the exposure of the Volkswagen emissions scandal, or “Dieselgate”, through ICCT research. To mark this occasion, which became a decisive moment for Europe’s automotive industry and real-world emissions testing across the globe, ICCT tells the story of how it all unfolded in a graphic novel.
Dieselgate FAQs
What is Dieselgate?
The Volkswagen emissions scandal, more commonly known as “Dieselgate,” was a scandal in which diesel passenger vehicles were found to emit far higher levels of pollutants during real-world driving than in laboratory tests due to software designed to cheat emissions measurements ,referred to as “defeat devices”. These illegal defeat devices ensured emission controls functioned during official testing but were disabled in real-world conditions, resulting in higher NOX emissions than reported. Subsequent investigations uncovered systemic misconduct, demonstrating that the problem extended beyond Volkswagen to the broader automotive industry.
What was ICCT’s role?
What are the health impacts of excess diesel emissions?
Nitrogen oxide emissions (NOx) from diesel cars, trucks, and buses are a major contributor to air pollution-related deaths worldwide. They are linked to a range of adverse health issues, including asthma in children and chronic obstructive pulmonary disease.
A 2025 report published by the Centre for Research on Energy and Clean Air (CREA), based on real-world data collated by the TRUE Initiative and ICCT, assesses the impact of suspiciously high emissions likely linked to the potential use of prohibited defeat devices. The findings reveal that between 2009 and 2024, these emissions have caused an estimated:
- 124,000 premature deaths
- 98,000 new cases of asthma in children
- 25,000 years lived with chronic obstructive pulmonary disease
- 15,000,000 days of sick leave
The associated economic burden of these health impacts equals €760 billion.
What impact did Dieselgate have?
The Dieselgate scandal prompted legal, regulatory, and industry responses. It revealed that prohibited defeat devices caused vehicles’ emission control systems to function normally during laboratory testing but were disabled during real-world driving, resulting in higher NOx emissions. The legal fallout of this scandal led to large fines and prison sentences for former Volkswagen managers.
Dieselgate had a lasting effect on vehicle regulation worldwide, prompting stricter regulatory frameworks and accelerating the shift toward more stringent emission standards and zero-emission vehicles. Governments in major vehicle markets, including Europe, China, India, South Korea, and the United States, now conduct real-world emissions testing during vehicle certification or throughout the vehicle’s life to prevent future use of defeat devices. The scandal also prompted developments aimed at improving regulation of NOx emissions: The EU type-approval framework was revised, requiring Member States to conduct a minimum number of independent tests annually to ensure ongoing compliance with emissions and safety standards.
In 2020, the Court Justice of the European Union clarified what constitutes a prohibited defeat device under EU rules in four rulings. Many of these prohibited strategies were common among diesel car manufacturers before the Real Driving Emissions testing procedure was introduced, offering grounds for reinvestigating diesel cars showing high NOx emissions.
In the automotive industry, Dieselgate spurred Volkswagen and other carmakers to make significant public pledges to transition toward electric vehicles. The scandal became a turning point, accelerating electrification efforts to restore trust and comply with increasingly strict emission regulations.
Despite this progress, millions of high-emitting diesel vehicles remain on roads worldwide. Work by The TRUE Initiative, which was founded on the heels of Dieselgate to serve as an independent source of real-world emissions data, reveals that even diesel vehicles certified to world class emission standards still sometimes emit 2 to 4 times the allowable limits of NOx. Both older vehicles and some newer models continue to exhibit excess emissions, an issue prevalent across manufacturers.
The TRUE Initiative: Closing the emissions gap
The Dieselgate scandal highlighted the disconnect between laboratory testing and real-world vehicle emissions. To fill this gap, The Real Urban Emissions (TRUE) Initiative was formed in 2017. A partnership between the ICCT and the FIA Foundation, the TRUE Initiative works to collect and analyze independent real-world emissions data, informing policymakers, manufacturers, and consumers of the real impact of vehicle emissions on air quality and public health.
Key Dieselgate Publications
More Publications
Dieselgate in the News
Engineering a Deception: What Led to Volkswagen’s Diesel Scandal
(New York Times)
Volkswagen: The scandal explained
(BBC)
‘Dieselgate’ defeat devices were illegal, top EU court confirms
(Euractiv)
(DW)
(Guardian)
(Politico)