Volkswagen installed software that cheated on emissions tests

In September 2015, the U.S. Environmental Protection Agency (EPA) discovered that Volkswagen had deliberately programmed diesel engines to produce false results during emissions testing. The software, called a "defeat device," detected when a car was being tested in a laboratory and switched the engine to a low-emissions mode. Once the test ended and the car was driven normally on the road, the engine switched back to a mode that produced up to 40 times the legal limit of nitrogen oxide (NOx) pollution.

This was not a manufacturing defect or an unintended consequence of engineering. Volkswagen engineers designed the deception intentionally, and the company's management knew about it. The scandal affected roughly 11 million vehicles worldwide, including approximately 500,000 sold in the United States between 2009 and 2015.

The when ready consequence was that Volkswagen faced criminal charges, paid billions in fines and settlements, and lost public trust. For owners of affected vehicles, the scandal created a choice: keep a car that polluted far more than advertised, or participate in a buyback or repair program.

Key Takeaways

  • Volkswagen programmed diesel engines to cheat on emissions tests by switching to a cleaner mode only during laboratory testing, then reverting to a high-pollution mode on the road.
  • The deception affected roughly 500,000 vehicles sold in the United States, mostly 2009–2015 model year Jettas, Passats, Beetles, and Golfs with 2.0-liter diesel engines.
  • Owners of affected vehicles could choose between a manufacturer buyback at a set price, a trade-in credit, or a software update that reduced engine performance to meet emissions standards.
  • The scandal led to criminal charges against Volkswagen, over $15 billion in U.S. fines and settlements, and a permanent shift in how the EPA monitors emissions compliance.
  • Emissions testing in the United States now includes real-world driving tests (called WLTP and RDE) in addition to laboratory tests, making defeat devices much harder to hide.

Which vehicles had the defeat device

The affected cars were Volkswagen and Audi diesel models sold in the United States between 2009 and 2015. The most common were the Volkswagen Jetta, Passat, Beetle, and Golf, all equipped with 2.0-liter turbocharged diesel engines. Audi A3 models with the same engine were also included. Later investigations found that some 3.0-liter diesel engines in larger Volkswagen and Audi vehicles, as well as Porsche Cayenne models, also contained defeat devices.

You can check whether your vehicle is affected by entering your Vehicle Identification Number (VIN) on the EPA's Volkswagen settlement website or by contacting a Volkswagen dealer. The VIN is printed on your registration and insurance documents, and also visible on the dashboard at the base of the windshield on the driver's side.

If your car is on the list, it means the engine was programmed to pass the EPA's laboratory test while emitting far more pollution during normal driving. This does not mean the engine will fail or stop working, but it does mean the actual emissions performance was misrepresented when you bought or leased the vehicle.

What owners could do: buyback, trade-in, or repair

Volkswagen offered affected owners three main options. The first was a manufacturer buyback, in which the company purchased the vehicle back at a price set by an independent appraiser, typically based on the car's condition and mileage at the time of the settlement. Owners who chose buyback received the appraised price plus a cash settlement, but had to return the vehicle to Volkswagen.

The second option was a trade-in credit, which allowed owners to keep their vehicle and receive a credit toward the purchase of a new Volkswagen. The credit amount was similar to the buyback price, making it a way to offset the cost of replacing the car.

The third option was a software update and cash settlement. Volkswagen modified the engine control software to remove the defeat device and bring emissions into compliance with EPA standards. However, this modification reduced fuel economy and engine performance—owners typically saw a 5 to 10 percent drop in fuel efficiency and slightly slower acceleration. Owners who accepted the software update received a cash payment but kept their vehicle.

The important date to make a choice has passed, and most owners have already selected one of these options. If you own an affected vehicle now, you inherited whatever choice the previous owner made. If your car still has the original defeat device software, you should contact a Volkswagen dealer to discuss the repair or buyback options that may still be available in your region.

Why the defeat device worked and why it was discovered

The defeat device worked because the EPA's emissions testing procedure, in place since the 1970s, was conducted entirely in a laboratory on a stationary dynamometer—essentially a treadmill for cars. The test followed a fixed driving pattern with predictable acceleration and speed changes. Volkswagen's software detected this pattern and recognized when the car was being tested.

During the test, the engine operated in a mode that used exhaust gas recirculation and other emission-control systems to reduce NOx output to legal levels. Once the test ended, the software switched to a mode that disabled some of these systems, allowing the engine to run more efficiently and produce more power—but at the cost of emitting 15 to 40 times the legal NOx limit.

The deception was discovered by researchers at West Virginia University who were conducting an independent study on real-world emissions. They drove a Volkswagen Jetta on public roads while measuring its actual exhaust output and comparing it to the laboratory test results. The discrepancy was so large that they contacted the EPA, which then launched an investigation.

The scandal exposed a fundamental weakness in the testing system: a laboratory procedure cannot detect software designed to behave differently in real-world conditions. In response, the EPA and the National Highway Traffic Safety Administration (NHTSA) began requiring real-world driving emissions tests, called the Worldwide Harmonized Light Vehicle Test Procedure (WLTP) and Real Driving Emissions (RDE) testing, for all new vehicles.

The legal and financial consequences for Volkswagen

Volkswagen faced criminal charges in the United States, Germany, and other countries. In the U.S., the company pleaded guilty to charges including conspiracy, obstruction of justice, and violation of the Clean Air Act. Several Volkswagen executives were also charged individually with fraud and conspiracy.

The financial penalties were substantial. Volkswagen paid over $15 billion in U.S. fines, settlements, and buyback costs. This included a $2.8 billion criminal fine, a $1.5 billion civil settlement with the EPA, and approximately $10 billion in buyback and repair costs for affected vehicle owners. The company also paid settlements in Europe and other regions.

Beyond the when ready penalties, Volkswagen's reputation suffered lasting damage. The scandal became synonymous with corporate deception and raised questions about the reliability of emissions testing across the entire automotive industry. It also accelerated Volkswagen's shift toward electric vehicles as a way to rebuild trust and comply with increasingly strict emissions regulations worldwide.

How emissions testing changed after 2015

Before the Volkswagen scandal, the EPA relied almost entirely on laboratory testing to certify that vehicles met emissions standards. The test was standardized, repeatable, and straightforward to conduct, but it did not reflect real-world driving conditions. After 2015, the EPA began requiring manufacturers to conduct real-world driving emissions tests in addition to laboratory tests.

The new testing procedure, called Real Driving Emissions (RDE), involves driving a vehicle on public roads with portable emissions measurement equipment installed. The test includes highway driving, city driving, and rural driving at various speeds and loads. Manufacturers must now demonstrate that their vehicles meet emissions standards not just in the lab, but under conditions that actual drivers experience.

The EPA also increased its own testing and monitoring. The agency now conducts surprise emissions tests on vehicles already on the road, comparing their real-world performance to their certified laboratory results. This makes it much harder for a manufacturer to hide a defeat device, because the software would have to fool both the laboratory test and the real-world test—a far more difficult engineering problem.

These changes explore to all new vehicles sold in the United States, not just Volkswagen. The result is that modern emissions certifications are more reliable and harder to cheat, though they also require more time and expense for manufacturers to complete.

Frequently Asked Questions

Do I need to do anything if I own an affected Volkswagen?

If you bought the vehicle after the settlement was announced in 2015, the previous owner likely already chose a buyback, trade-in, or repair option. You can check your vehicle's status by contacting a Volkswagen dealer with your VIN. If the software update has already been applied, no further action is needed. If not, the dealer can explain what options remain available in your area.

Will the software update hurt my car's performance?

The software update removes the defeat device and brings emissions into legal compliance, but it does reduce fuel economy by roughly 5 to 10 percent and may slightly reduce acceleration. The trade-off is that your vehicle will no longer emit excessive pollution. If you want to avoid this performance loss, the buyback or trade-in options were available during the settlement period.

Why didn't the EPA catch this sooner?

The EPA's testing procedure was laboratory-based and followed a predictable pattern, which made it possible for software to detect when it was being tested. The agency did not have the tools or authority to conduct widespread real-world emissions testing before the scandal. After 2015, the EPA implemented real-world testing requirements and increased its monitoring of vehicles already on the road.

Did other manufacturers use defeat devices?

The Volkswagen scandal prompted investigations into other manufacturers, and some were found to have used questionable emissions-control strategies, though not defeat devices as deliberate as Volkswagen's. The scandal led to stricter oversight of all manufacturers and more rigorous testing procedures across the industry.

Can I sue Volkswagen if I own an affected vehicle?

The major class-action settlements in the United States have already been resolved, and the important date to join them has passed. If you own an affected vehicle now, you inherited the previous owner's settlement choice. You may have other legal options depending on your state and the circumstances of your purchase, but you should consult an attorney for information specific to your situation.