What Volkswagen Did and Why It Matters

Between 2009 and 2015, Volkswagen installed software in nearly 11 million diesel vehicles worldwide that detected when the car was undergoing an emissions test and switched the engine to a lower-pollution mode only during that test. In normal driving, the cars emitted nitrogen oxides at levels up to 40 times higher than what the software reported during testing. The company knew the vehicles could not meet real-world emissions standards honestly, so it programmed them to cheat.

Volkswagen disclosed the scheme in September 2015 after the Environmental Protection Agency (EPA) and California Air Resources Board (CARB) discovered the discrepancy. The scandal affected diesel models including the Jetta, Golf, Passat, Beetle, and Audi A3, primarily in the United States, though the practice occurred globally. The company paid over $14 billion in fines, settlements, and buyback programs in the U.S. alone, and faced criminal charges against executives in multiple countries.

The scandal matters to you because it exposed a gap in how emissions testing worked and forced regulators to redesign the testing process itself. It also created a legal pathway for owners of affected vehicles to seek compensation or vehicle buybacks, and it changed how manufacturers approach emissions compliance going forward.

Key Takeaways

  • Volkswagen programmed diesel engines to emit far less pollution during official tests than during normal driving, a practice that went undetected for years.
  • The EPA and California regulators discovered the cheating through real-world testing, not through the official test cycle, which led to major changes in how cars are tested.
  • Owners of affected Volkswagen and Audi diesel vehicles were offered buybacks, cash settlements, or engine modifications depending on the model year and location.
  • The scandal prompted the EPA and other regulators to adopt more realistic testing methods that measure emissions during actual driving conditions, not just in controlled lab settings.

How the Cheating Software Worked

The software, called a "defeat device," monitored several inputs: steering wheel angle, vehicle speed, engine load, and barometric pressure. When the car detected it was on a dynamometer (the treadmill-like machine used in official emissions tests), it activated a special emissions control mode. In this mode, the engine ran cooler and richer, reducing nitrogen oxide output to levels that passed EPA standards.

Once the test ended and the car returned to normal driving, the software switched back to the standard engine map, which prioritized fuel economy and performance over emissions control. The difference was dramatic: in real driving, the affected cars produced 15 to 40 times more nitrogen oxides than the test results showed. Nitrogen oxides contribute to smog and respiratory illness, particularly in children and people with asthma.

Volkswagen engineers built the system deliberately. Internal emails and testimony later revealed that the company knew the diesel engines could not meet U.S. emissions standards under real-world conditions and chose deception over redesign. The company marketed these vehicles as "clean diesel" and "TDI" (turbocharged direct injection) models, emphasizing their fuel economy while hiding their actual pollution output.

Why Regulators Missed It for Years

The official EPA emissions test, called the Federal Test Procedure (FTP), was conducted in a controlled laboratory on a dynamometer. The test followed a fixed driving pattern with predetermined speeds and acceleration rates. Because the pattern was public and predictable, Volkswagen's engineers could program the software to recognize it precisely.

The EPA did not routinely test vehicles on real roads under real conditions. Regulators assumed that if a car passed the lab test, it would perform similarly in actual driving. This assumption proved wrong. In 2014, researchers at West Virginia University conducted real-world testing on a Volkswagen Jetta and discovered massive discrepancies between lab results and on-road emissions. Their findings eventually reached the EPA and triggered the investigation that exposed the scandal.

The scandal revealed a fundamental flaw in the testing system: a test conducted under identical, repeatable conditions in a lab does not measure how a vehicle actually pollutes in the varied, unpredictable conditions of real driving. Manufacturers had incentive to optimize their vehicles for the test rather than for real-world performance.

Changes to Emissions Testing After the Scandal

The EPA and California regulators redesigned the emissions testing process to prevent similar cheating. The new approach, called the Worldwide Harmonized Light Vehicle Test Procedure (WLTP), replaced the older FTP in 2017 for new vehicles. WLTP uses a more realistic driving pattern with higher speeds, longer acceleration periods, and varied conditions that better reflect actual driving.

More importantly, regulators now conduct on-road testing using portable emissions measurement systems (PEMS). These devices attach to vehicles and measure real-world pollution as the car drives on public roads. Manufacturers cannot predict or optimize for these tests because the driving conditions are not fixed. On-road testing is now a standard part of EPA certification for new vehicles.

The EPA also tightened the rules around defeat devices. Any software that reduces emissions control effectiveness outside of specific, documented conditions is now prohibited. Manufacturers must disclose all emissions-related software and justify why it exists. Penalties for violations increased substantially, and the EPA now conducts more frequent and random testing of in-use vehicles.

What Happened to Volkswagen Owners

Volkswagen settled with the EPA, the Federal Trade Commission (FTC), and California regulators. The company offered affected owners three options: a buyback at the vehicle's pre-scandal value, a cash settlement, or an engine modification that would bring the car into compliance with emissions standards.

The buyback program ran from 2016 through 2018 and covered 2009–2015 model year diesel vehicles. Owners received the original purchase price minus depreciation, and Volkswagen took ownership of the cars. Most of these vehicles were later scrapped or exported, as they could not be legally sold in the United States without modification.

Owners who chose the cash settlement received between $5,100 and $10,000 depending on the model and year, in addition to the option to keep the vehicle. Those who accepted the engine modification received a software update and hardware changes designed to reduce nitrogen oxide emissions. The modifications reduced fuel economy slightly and, in some cases, reduced engine performance, which led some owners to pursue legal action against Volkswagen for diminished vehicle value.

Ongoing Legal and Regulatory Consequences

Beyond the EPA settlement, Volkswagen faced criminal charges. In 2017, the company pleaded guilty to three felonies: conspiracy, obstruction of justice, and violation of the Clean Air Act. The company paid a $2.8 billion criminal penalty. Several Volkswagen executives faced individual criminal charges in the United States and Europe, though some fled or fought extradition.

Volkswagen also paid settlements to state attorneys general, environmental groups, and private owners who filed class-action lawsuits. The total cost to the company exceeded $30 billion globally when including fines, settlements, buybacks, and legal fees. The scandal damaged the company's reputation and slowed its diesel sales in the United States, which never fully recovered.

The scandal also prompted regulators in Europe, India, and other regions to investigate their own emissions testing procedures and to conduct real-world testing of vehicles already on the road. Several other manufacturers were found to have similar discrepancies between lab and real-world emissions, though none as deliberate or widespread as Volkswagen's.

What This Means for Emissions Testing Today

The Volkswagen scandal fundamentally changed how regulators approach emissions certification. Testing is now more realistic, harder to game, and includes real-world measurement. Manufacturers can no longer rely on a single, predictable lab test to prove compliance.

However, the scandal also revealed that even with stronger testing, enforcement depends on regulators having the resources and authority to conduct frequent, random testing of vehicles in use. The EPA's budget for vehicle testing has increased since 2015, but it remains limited compared to the number of vehicles on the road. Regulators now prioritize testing of high-volume models and manufacturers with a history of violations.

For consumers, the scandal underscored the importance of independent testing and transparency. Environmental groups and academic researchers now conduct their own emissions testing and publish results publicly, creating a check on manufacturer claims. If you are considering a diesel vehicle, you can now find real-world emissions data from sources like the International Council on Clean Transportation (ICCT), which first publicized the Volkswagen discrepancy.

Frequently Asked Questions

Did Volkswagen vehicles with the defeat device cause health problems?

The excess nitrogen oxides from these vehicles contributed to air pollution and likely caused respiratory harm, particularly in areas with high concentrations of affected cars. Researchers have estimated that the excess emissions from Volkswagen's fleet caused thousands of premature deaths over the years the vehicles were on the road, though attributing specific health outcomes to specific vehicles is not possible.

Can I still buy a used Volkswagen diesel from that era?

Yes, but you should know its history. Many affected vehicles were bought back and scrapped, but some remain in private hands. If you purchase one, it likely has the emissions modification installed, which reduces but does not eliminate the performance and fuel economy penalty. Check the vehicle history report to see if it was part of the recall program.

Did other car manufacturers cheat on emissions tests?

Volkswagen's scheme was the most deliberate and widespread, but regulators have found smaller discrepancies between lab and real-world emissions in vehicles from other manufacturers. These discrepancies appear to result from how manufacturers optimize engines for the test cycle rather than from intentional defeat devices. Real-world testing has made these gaps harder to hide.

How accurate are emissions tests now?

Modern testing is more realistic than before the scandal, but no test perfectly captures all real-world driving conditions. On-road testing with PEMS equipment measures actual emissions, but results vary based on traffic, weather, driving style, and road conditions. The goal is not perfect prediction but rather a test that manufacturers cannot easily optimize for without improving real-world performance.

What should I look for if I want a low-emissions vehicle?

Look for real-world emissions data from independent sources, not just manufacturer claims or lab test results. The EPA's website lists real-world fuel economy and emissions estimates for new vehicles. For used vehicles, check whether the model has a history of emissions violations or recalls. Electric and hybrid vehicles have lower real-world emissions than traditional gasoline or diesel engines.