The US Department of Justice has sued Volkswagen Group (PDF) in a Michigan District Court on behalf of the Environmental Protection Agency (EPA), alleging that the automaker installed illegal defeat devices on almost 600,000 diesel passenger vehicles.

The lawsuit is the latest chapter in the fallout since the EPA published a notice of violation in September accusing Volkswagen of installing software on many of its diesel vehicles that would stop the car’s emissions control system from working properly during normal driving, but engage the emissions control system while the car was being tested in a lab, effectively helping Volkswagen cheat air quality regulators in the US.

A press release from the EPA said that approximately 499,000 diesel cars with 2.0 liter engines were found to have defeat devices, and some 85,000 cars with 3.0 liter engines were similarly implicated. The complaint filed by the Department of Justice suggests that the software to defeat the emissions control system in 2.0 and 3.0 liter cars was slightly different, however.

According to the complaint, during federal emissions testing, 2.0 liter engines from Volkswagen "run software logic and/or calibrations that produce compliant emission results” which the car's onboard system calls the “dyno calibration,” referring to the dynamometer that's used during emissions testing.

"At all other times during normal vehicle operation, the 2.0L Subject Vehicles’ ECM [electronic control module] software run a separate 'road calibration' that reduces the effectiveness of the emission control system.” The difference between the dyno calibration and the road calibration resulted in the widely quoted statistic that Volkswagen cars were releasing up to 40 times the permitted amount of nitrogen oxide (NO x ).

Volkswagen’s offending 3.0 liter diesel engines, however, "run software logic and/or calibrations that produce compliant emission results under an ECM calibration referred to as the “temperature conditioning mode.” At other times during normal vehicle operation, the 3.0L Subject Vehicles’ ECM software run a separate “normal mode” that reduces the effectiveness of the emission control system.” The result of these two modes was "increased NO x emissions by a factor of up to 9 times above the EPA-compliant levels.”

In the complaint, the DoJ notes that NO x is a highly reactive gas that can exacerbate asthma, emphysema, and congestion. "Additionally, recent scientific studies indicate that the direct health effects of NO x are worse than previously understood, including respiratory problems, damage to lung tissue, and premature death,” the complaint notes.

In addition to its accusations regarding defeat devices on Volkswagen Group cars, the Department of Justice accused the company of lying to or misleading federal regulators:

The United States’ efforts to learn the truth about the emission exceedances and other irregularities related to the 2.0L Subject Vehicles, including whether VW had committed the violations of federal law alleged herein, were impeded and obstructed by material omissions and misleading information provided by VW entities including at least VWoA and Volkswagen AG. Even after EPA issued its September 18, 2015 Notice of Violation to Volkswagen AG, Audi AG, and VWoA, and Mr. Horn’s testimony before Congress, VW failed to come forward and reveal to regulators that the 3.0L Subject Vehicles contain one or more undisclosed AECDs, including the dual calibration strategy involving the “temperature conditioning mode” and the “normal mode.” The existence of this dual calibration strategy was uncovered only as a result of EPA and CARB’s diligence.

The DoJ and the EPA are asking the court to halt the sale of any vehicle that has been identified to include a defeat device and order the company to remedy the situation by fixing the affected cars. In addition, the US says that Volkswagen Group must pay civil penalties of $32,500 per affected car made before 2009 and $37,500 per affected car made after 2009 for each of two violations of the Clean Air Act, as well as between $2,750 and $3,750 for each defeat device found on the affected cars. Finally, US officials are demanding "up to $32,500 per day of violation occurring before January 13, 2009, and up to $37,500 per day of violation occurring on or after January 13, 2009 for violations of Section 203(a)(2) of the [Clean Air] Act.”

In a statement, Volkswagen Group of America said, "Volkswagen will continue to work cooperatively with the EPA on developing remedies to bring the TDI [turbocharged direct injection] vehicles into full compliance with regulations as soon as possible. In addition, we are working with Kenneth Feinberg to develop an independent, fair and swift process for resolving private consumer claims relating to these issues. We will continue to cooperate with all government agencies investigating these matters."

According to the EPA, the affected cars include the following:

2.0 liter diesel models and model years:

Jetta (2009-2015)

Jetta Sportwagen (2009-2014)

Beetle (2013-2015)

Beetle Convertible (2013-2015)

Audi A3 (2010-2015)

Golf (2010-2015)

Golf Sportwagen (2015)

Passat (2012-2015)

3.0 liter diesel models and model years:

Volkswagen Touareg (2009-2016)

Porsche Cayenne (2013-2016)

Audi A6 Quattro (2014-2016)

Audi A7 Quattro (2014-2016)

Audi A8 (2014 – 2016)

Audi A8L (2014-2016)

Audi Q5 (2014-2016)

Audi Q7 (2009-2015)

Listing image by Thomas Hawk