Investigators probing U.S. models of Mercedes-Benz sold with diesel engines have found software, possibly illegal under EPA rules, that helped them pass emission tests.

Such software may be similar to that notoriously used in 580,000 vehicles sold by VW, Audi, and Porsche from 2009 through 2015 in what became the Volkswagen diesel emission scandal.

Different VW Group vehicles were fitted with "defeat device" software that detected testing routines and controlled emissions more aggressively than in regular use.

CHECK OUT: VW exec pleads guilty to diesel cheating charges after jail, house arrest

The report was first published on Sunday by Bild am Sonntag, a German business newspaper that intensively covers Germany's automakers and vehicle industry.

The paper cited confidential documents, according to a summary by Bloomberg published the same day.

According to the report, one routine identified by investigators switched off emission controls after 26 kilometers (16 miles) of operation.

Volkswagen TDI 'clean diesel' television ad screencap

Volkswagen TDI 'clean diesel' television ad screencap

Another set of code, similar to one said to have been used by Volkswagen engineers, identified when the car was undergoing emission tests based on a known pattern of acceleration and other factors.

The German paper said the investigators had e-mails from engineers at Daimler, the parent company of Mercedes-Benz, that questioned whether those routines were legal.

VW Group cars were also found to contain undeclared and unapproved routines that boosted emissions under the pretext of protecting the engine from damage.

CHECK OUT: EU investigating diesel collusion among Audi, BMW, Mercedes, Porsche, VW: report (Jul 2017)

Mercedes-Benz pioneered the use of diesel engines in passenger vehicles as early as 1936, and the company has sold them longer in the U.S. than any other maker.

For the 2018 and 2019 model year, however, it has withdrawn all diesel variants from its U.S. lineup, citing reduced buyer interest in an era of low fuel prices across the board.

That leaves BMW as the sole German maker offering diesels to U.S. customers. Other diesel passenger models are offered this year by Chevrolet, GMC, and (purportedly) Mazda, along with diesel options for various sizes of full-size pickup trucks.