Over the weekend, Volkswagen Group and its luxury brand Audi confirmed that certain Audi models are currently under investigation by US and European authorities, apparently for irregularities involving emissions numbers from gas- and diesel-powered automatic transmission vehicles.

Last week, the German magazine Bild Am Sontag reported that California’s Air Resources Board (CARB) had discovered emissions irregularities on unspecified Audi models separate from the diesel scandal that has wracked VW, Audi, and Porsche brands. Neither VW Group nor CARB confirmed the reports to any outlet, but Audi said that it would “continue to work with regulators.”

This fresh wrinkle in VW Group's plans appears to be related to how certain Audi vehicles respond when the steering wheel is never moved more than 15 degrees during a drive. If the steering wheel hardly moves, the car assumes it's undergoing a treadmill test and seemingly curtails carbon dioxide (CO 2 ) emissions. According to a source speaking to The Wall Street Journal, as well as an internal Audi document the paper obtained, “Audi engineered the automatic transmissions to run at very low RPMs during treadmill tests to pass emissions tests, but then to run at full performance on the road, resulting in higher greenhouse gas emissions.”

The Environmental Protection Agency (EPA) declined to comment to Ars, but Bild Am Sontag reported this weekend that the agency will meet with senior VW Group engineers later this week. Reuters reports the agency is looking into whether this mechanism for reducing emissions during lab tests constitutes a defeat device.

VW Group told Reuters on Saturday that Audi’s cars have adaptive shift programs that “can lead to incorrect and non-reproducible results" during laboratory tests. "In normal use, these adaptive systems support the driver by adjusting the gear-shifting points to best adapt to each driving situation," VW Group added.

The WSJ says that the cars with the transmissions in question are primarily Audi A6 and A8 sedans and the Q5 SUV. A source speaking to the paper added that Audi disabled the ability to recognize test conditions just before VW Group admitted to manipulating test data in the diesel scandal in 2015.