The German government’s pressure on Fiat-Chrysler Automobiles for potentially using a “cheat” device on tested diesel-engine vehicles took another turn.

Germany has sent letters to the European Commission and Italian Transport Ministry on finding unusual increases in emission of four Fiat Chrysler vehicles. The test results showed the “illegal use of a device to switch off exhaust treatment systems,” according to the letters, which were also viewed and reported on by Reuters.

Tests commissioned by the German government found a “special nitrogen oxide catalyst which is being switched off after a few cleaning cycles,” according to WirtschaftsWoche magazine. Affected vehicles run off Fiat’s latest 2.0-liter diesel and include the Fiat 500X and Jeep Renegade small SUVs and its platform siblings, along with the Fiat Doblo van.

FCA’s vehicles conform to current emissions rules and don’t include defeat devices, an FCA spokesman said.

The European Commission responded by saying that it is the responsibility of the Italian government to resolve the problem in communication with Germany. “It is first and foremost a dialogue between the two member states concerned, with an obligation to keep the Commission informed and the possibility for the Commission to facilitate a solution if no agreement can be found,” the Commission said in a statement.

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The tension between the two countries goes back to May when a German transport authority criticized FCA for not attending a meeting discuss the irregularities discovered on its diesel vehicle emissions. The following month, Italian Transport Minister Graziano Delrio said that Fiat diesel engines had been tested and found to comply with Italian emissions regulations.

It all started with a probe by the KBA, the federal motor transport authority, which found that some Fiat vehicles showed irregular levels of diesel exhaust pollution, the Bild am Sonntag newspaper reported earlier this year. The newspaper reported that the Fiat emissions treatment system was throttled back after 22 minutes, and that the regulatory tests were typically lasting about 20 minutes.

After the Volkswagen emissions scandal broke, the KBA had been testing 53 different vehicles made by several automakers. The agency found that some were manipulating data captured during what they described as a “thermal window.” That term refers to a period when automakers are given flexibility to throttle back on emissions management systems to protect engines from condensation and other hazards in very cold conditions. During the investigation, KBA found that automakers were using a very wide range of temperatures for thermal windows.

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