The US EPA announced on Monday that a notice of violation, or NOV, of the Clean Air Act was issued to Volkswagen. The EPA states that the model years 2009-2015 Volkswagen and Audi vehicles (4-cylinder diesels) included software that allowed the cars to evade some emissions standards.

Cynthia Giles, the Assistant Administrator for the Office of Enforcement and Compliance Assurance, stated, “Working closely with the California Air Resources Board, EPA is committed to making sure that all automakers play by the same rules. EPA will continue to investigate these very serious matters.”

The NOV explains that these vehicles had software that turns on “full emissions control” only during automotive emissions testing and not during everyday use. This allowed the cars to pass the test but to emit NOx (nitrogen oxides) at up to 40 times the permitted allowance. The EPA defines this as a “defeat device” as it was designed specifically to evade testing.

This follows a 1.1 million dollar fine that Volkswagen paid back in 2005 when they failed to report the defect oxygen sensor that affected 199-2001 vehicles. These vehicles produced “thousands of tons of harmful pollutants including nonmethane hydrocarbons (NMHC) and carbon monoxide (CO). NMHC are key reactants in the production of ozone, a major contributor to cancer-causing smog.” (Volkswagen of America, Inc., Agrees to Pay More Than $1 Million for Clean Air Act Violation, Release Date: 06/15/2005)

To read the full NOV, check out the full post on the EPA site.