Yesterday, the United States Environmental Protection Agency (EPA) issued a second notice of violation (NOV) of the country’s Clean Air Act (CAA) to the Volkswagen Group. The NOV involves the Group’s 3.0 litre TDI V6 engine used in Volkswagen, Audi, and Porsche passenger vehicles.

Following the issuance of the NOV, Porsche Cars North America has now issued a stop-sale order of all model year 2014 through 2016 Porsche Cayenne diesel SUVs in the country. In its official press release, Porsche deemed EPA’s act of issuing the second NOV as “unexpected” and its follow-up action of discontinuing sales of the diesel Cayennes was done “voluntarily.”

The second NOV issued to the five companies within the Volkswagen Group’s umbrella, covered the same issue relating to defeat devices installed on its diesel vehicles. The devices are able to detect when the vehicle is being put through an emissions test, and engage certain measures to ensure it passes the test.

Once the vehicle detects that it is not undergoing testing, the device will then revert the vehicle back to its “normal” setting, resulting in higher emissions compared to the results obtained when testing. The NOV stated that for the 3.0 litre TDI V6 engine, nitrogen oxide (NOx) emissions was up to nine times of the EPA’s standard.

Other diesel models from the Volkswagen Group that were named in the NOV besides the Porsche Cayenne, include the Volkswagen Touareg, and from Audi, the A6 quattro, A7 quattro, A8, A8L, and Q5. The NOV covers roughly 10,000 diesel passenger cars already sold in the US since model year 2014. However, the number of 2016 vehicles covered by the NOV has yet to be known.