Volkswagen diesel-powered cars—marketed to consumers as “clean diesels”—emit up to 40 times more pollutants than allowed by federal pollution standards because of software designed to intentionally fake emissions testing results, officials with the company have admitted. About 11 million Volkswagen cars worldwide—including more than 500,000 vehicles in the U.S.—were sold by the company with the deceptive emissions software. Experts have predicted that Volkswagen could face billions in fines from federal regulators as well as numerous class action lawsuits from vehicle owners in what some experts are calling one of the biggest cases of automotive fraud in recent history.

Volkswagen’s deliberate effort to evade emissions test requirements for its diesel-powered vehicles came to light as a result of testing by the International Council on Clean Transportation, a non-profit environmental group that wanted to test how “clean diesel” cars performed under real world conditions. After tests of Volkswagen diesel cars revealed higher-than-expected levels of emissions, the groups enlisted the help of researchers from West Virginia University and the California Air Resources Board to conduct further tests of the Volkswagen vehicles. These tests revealed that although the vehicles emitted lower levels of pollutants during state emissions testing, the Volkswagen diesel cars released 30-40 times more pollutants than emissions standards under real world driving conditions.

Volkswagen initially attempted to explain the test results as a result of technical issues or problems with the testing protocol.  Volkswagen quietly recalled thousands of vehicles in order to purportedly fix the problem.  The problem, however, was not fixed.  Finally, officials from the Environmental Protection Agency threatened to withhold approval of the company’s 2016 Volkswagen and Audi diesel models.  At this point, Volkswagen was forced to admit that the discrepancy between the diesel models’ laboratory and real world emissions output was the result of software designed by the company to intentionally mislead federal regulators and defraud consumers.

According to the company’s admission, Volkswagen diesel vehicles with 2-liter Type EA 189 engines were equipped with software that was programmed to sense when the vehicles were undergoing emissions testing. The software turned on equipment in the vehicle that lowered emissions levels, enabling the cars to pass pollution tests.  Once the tests were complete, the secret software was turned off and the cars returned to producing emissions far in excess of federal standards.