In the aftermath of the Volkswagen (VLKAY) emissions manipulation scandal, things for the giant German car maker appear to be going from bad to worse with every passing week.

The latest revelation comes from Bild am Sonntag which, following last week’s news that even gasoline engines are now getting dragged into what until recently was exclusively a diesel issue, reports that several Volkswagen engineers have admitted manipulating carbon dioxide emissions data, saying the ambitious goals set by former Chief Executive Martin Winterkorn were difficult to achieve. As Reuters reports, VW engineers tampered with tyre pressure and mixed diesel with their motor oil to make them use less fuel, a deception that began in 2013 and carried on until the spring of this year.

“Employees have indicated in an internal investigation that there were irregularities in ascertaining fuel consumption data. How this happened is subject to ongoing proceedings,” a Volkswagen spokesman said, declining to comment on the Bild report.

Bild adds that former CEO Winterkorn declared at the Geneva auto show in March 2012 that VW wanted to reduce its CO2 emissions by 30 percent by 2015 and the engineers did not dare to tell him that this would be difficult to achieve.

Volkswagen has declined to comment on whether the firm’s culture or the management style of Winterkorn, who resigned in September, had been a factor in the cheating – perhaps not surrounding himself with “yes” men would have prevented the dramatic fallout which according to analysts could result in a bill as high as $38 billion for fines, lawsuits and refits.

The revelation took place at the end of October when an engineer at VW’s headquarters in Wolfsburg, who works in the Research & Development department, broke his silence and told his superiors about the large-scale deception, Bild said citing only what it said was information it had received.

It said the engineers used several illegal measures to manipulate the emissions values, including through a higher tyre pressure of 3.5 bar. They also mixed diesel in the motor oil so that the vehicle ran more smoothly and used less fuel.