In September 2015, Volkswagen admitted to a secret that changed the car industry. The company had installed software in millions of diesel cars to cheat on emissions tests. This software, known as a defeat device, let cars pass pollution tests while releasing much higher levels of harmful gases during normal driving.
The scandal, known as Dieselgate, led to lawsuits in North America, Europe, and Asia, making it one of the largest legal battles in corporate history. Volkswagen faced criminal charges, government fines, and claims from car owners who felt misled. The company also had to deal with the health effects of its actions. Cars fitted with defeat devices released extra nitrogen oxide, a gas linked to breathing problems and other health risks.
This scandal did more than hurt Volkswagen’s reputation. It raised questions about how car companies are tested and regulated around the world. The following sections look at how the case grew into lawsuits across three continents, and what it means for public health and corporate honesty today.
How Volkswagen Cheated Emissions Tests
Volkswagen used hidden software to trick emissions tests on millions of diesel vehicles. This software let cars pass lab tests while polluting far more on real roads.
The Defeat Device and Test-Mode Detection
Volkswagen installed software known as a defeat device in its diesel engines. This software could tell when a car was being tested in a lab.
The software looked for signs of testing. These signs included the position of the steering wheel, the speed of the car, and how long the engine had been running.
When the software detected a test, it turned on full emissions controls. This made the car appear clean and within legal limits.
Once the car left the lab and drove on real roads, the software switched to a different mode. In this mode, emissions controls were reduced or turned off. Volkswagen Group used this method across many diesel passenger vehicles between 2009 and 2015.
Discovery, Investigation, and Regulatory Action
The Volkswagen emissions scandal did not begin with a company confession. It started with independent research that exposed a gap between lab results and real-world pollution levels, which then triggered a formal government investigation and years of legal action.
ICCT and On-Road Testing Evidence
The International Council on Clean Transportation (ICCT) funded a study in 2014 to show that clean diesel technology could work well in the United States and Europe. Researchers tested diesel vehicles on real roads instead of only in a lab.
The results did not match what regulators expected. Some vehicles produced up to 40 times more nitrogen oxide (NOx) emissions during road tests than during standard lab tests.
This gap did not make sense to the researchers. Volkswagen vehicles passed lab tests easily but polluted far more when driven under normal conditions. The ICCT shared these findings with the California Air Resources Board (CARB) and the U.S. Environmental Protection Agency (EPA). This data became the starting point for a deeper federal investigation.
The EPA Notice of Violation
In September 2015, the EPA issued a formal notice of violation to Volkswagen. The agency stated that the company had installed illegal software in about 500,000 diesel vehicles sold in the United States.
This software acted as a “defeat device.” It could detect when a car was being tested and would then adjust the engine to lower emissions only during that test.
Once the vehicle went back on the road, emissions controls would relax. NOx output would rise far above legal limits. The EPA’s notice confirmed that Volkswagen had known about this system and used it on purpose. This announcement led to immediate media attention and public backlash worldwide.
The Clean Air Act and U.S. Enforcement
The EPA’s notice was based on violations of the Clean Air Act, a federal law that sets emission standards for vehicles sold in the U.S. Under this law, automakers must certify that their vehicles meet these standards under normal driving conditions, not just in controlled test settings.
The U.S. Department of Justice joined the case soon after the EPA’s announcement. Together, these agencies pursued both civil and criminal penalties against Volkswagen.
In 2017, Volkswagen pleaded guilty to three criminal charges, including obstruction of justice and using defeat devices to cheat emissions tests. The company agreed to pay over $4.3 billion in fines. Several Volkswagen executives also faced individual criminal charges in the U.S. This set the stage for later scrutiny by the European Commission and regulators worldwide.
The Legal Fallout Across Three Continents
Dieselgate did not stay contained to one country. It spread into courtrooms and regulatory offices across North America, Europe, and Asia, each region handling the scandal in its own way.
United States Criminal Cases, Settlements, and Buybacks
The U.S. Department of Justice led one of the toughest responses to the scandal. Volkswagen pleaded guilty to criminal charges tied to the emissions fraud.
The company agreed to pay a $2.8 billion criminal penalty. It also faced civil penalties and separate settlements that pushed its total U.S. costs into the billions.
Former CEO Martin Winterkorn was charged as part of the investigation, though his case moved slowly due to his location in Germany. U.S. authorities also prosecuted other Volkswagen executives and engineers involved in the deception.
Volkswagen agreed to buy back or fix hundreds of thousands of affected diesel vehicles. Owners could choose a buyback, a lease termination, or an approved repair, along with cash compensation.
European Consumer Claims and Regulatory Proceedings
In Europe, the response centered on consumer lawsuits and regulatory action. The European Commission examined how emissions testing rules had been ignored across the industry, not just at Volkswagen.
Courts across EU member states ruled in favor of consumers who bought affected vehicles. Some rulings ordered compensation for owners, even without proof of individual financial loss.
Volkswagen Group brands faced scrutiny beyond the original VW nameplate. Audi and Porsche were both linked to similar emissions manipulation software.
Other automakers were drawn into related investigations. Mercedes-Benz faced regulatory questions in Germany, while Renault and the Renault-Nissan alliance dealt with separate emissions-related probes in France. Peugeot Citroën also faced scrutiny under French investigations into diesel emissions compliance.
Litigation and Enforcement Beyond Europe and North America
Outside Europe and North America, the legal fallout took a different shape. Fewer criminal cases emerged, but regulatory bodies in several countries opened investigations into whether local emissions standards had been violated.
South Korea fined Volkswagen and Audi for false advertising and ordered a recall of affected vehicles. Authorities also revoked some vehicle certifications, cutting off sales of certain models.
In Asia and other regions, enforcement often focused on administrative penalties rather than lengthy court battles. Some countries reached settlements with Volkswagen without extensive litigation.
Automakers like Nissan and Ford, both with major markets in Asia, faced separate scrutiny tied to broader emissions compliance reviews, though not always connected directly to the original Dieselgate case.
