BERLIN (Reuters) -- Several Volkswagen engineers have admitted manipulating carbon dioxide emissions data because goals set by former CEO Martin Winterkorn were difficult to achieve, Bild am Sonntag reported.
The paper said VW engineers tampered with tire 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.
Volkswagen on Tuesday said it had understated the fuel consumption and carbon dioxide emissions of about 800,000 vehicles sold in Europe and later said it would foot the bill for extra taxes incurred by drivers as a result.
The latest allegation has deepened a crisis which erupted in September when VW admitted it had rigged U.S. nitrogen oxides emissions tests. Auto analysts say the company could face a bill as high as 35 billion euros ($38 billion) for fines, lawsuits and vehicle refits.
Volkswagen is encouraging its rank-and-file staff to cooperate with its internal investigation by promising not to fire or sue them for any misconduct although high-level managers would still be held to account, a person familiar with the matter said.
According to Bild, 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. Lawyers for Winterkorn have not responded to a request for comment.
An engineer at VW's headquarters in Wolfsburg, who works in the r&d department, broke his silence at the end of October and told his superiors about the large-scale deception, Bild said citing only what it said was information it had received.
Volkswagen's supervisory board is scheduled to convene on Monday for the first time in about a month, in a meeting also to be attended by CEO Mueller, to take stock of the fallout from the widening scandal, two people familiar with the matter told Reuters.
The non-executive board, which includes the state premier of VW shareholder Lower Saxony, labor representatives as well as members of the founding Piech and Porsche families, is not expected to decide on funding measures but rather to assess the scale of the damage, the sources added.
Bild said the engineers used several illegal measures to manipulate the emissions values, including through a higher tire pressure. They also mixed diesel in the motor oil so that the vehicle ran more smoothly and used less fuel.
VW is conducting an internal investigation into its handling of all pollution-related issues after admitting that it had cheated on diesel nitrogen oxides emissions tests in the United States.
Sueddeutsche Zeitung reported on Saturday that VW managers were worried about traveling to the United States because U.S. investigators have confiscated the passport of an employee. The person had been in the U.S. for several weeks and was involved in dealing with the emissions scandal, the Financial Times said in a separate report.