The "Bild am Sonntag" newspaper reported Sunday that an engineer with Volkswagen's research and development department in Wolfsburg told his supervisors about carbon dioxide emissions fraud in the carmaker's models at the end of October.

Other VW employees have also since admitted to knowledge of the scam, the paper reported.

The German automaker is already reeling from a massive, separate scandal after it was revealed in September that the company had installed cheating software in around 11 million of its diesel-engine cars to thwart emission tests around the world. That scandal had centered on nitrogen oxide emissions. But on Tuesday, the company admitted that it had understated carbon dioxide emissions and fuel consumption of an additional 800,000 vehicles sold in Europe.

According to the weekly paper's report, tampering with CO2 emissions began in 2013 and continued until early 2015. The technicians had allegedly manipulated emissions values by increasing tire pressure to over 3.5 bar, and by mixing diesel into the engine oil to make the car consume less fuel.

Engineers reportedly said they were not able to meet the ambitious goals set by former CEO Martin Winterkorn, who stepped down in the wake of the scandal. In March 2012, Winterkorn had announced that VW would cut CO2 emissions by 30 percent by 2015.

Emissions tests are important criteria for taxing cars in many countries, especially in Europe.

Travel fears

Meanwhile, according to a separate report in the "Suddeutsche Zeitung," VW managers have expressed apprehension about traveling to the United States after American investigators confiscated the passport of an employee who is there on a visit.

The newspaper cited company sources as saying that management believed investigators aimed to prevent the employee from evading questioning or criminal prosecution over the emissions scandal. It said the new VW CEO, Matthias Müller, was unlikely to go ahead with a planned trip to the US later this month.

However, a spokesman for the company said "employees are still travelling to the United States. Everything else is speculation."

VW has set aside 6.5 billion euros ($7.3 billion) to cover fines and recalls, although it's likely the eventual cost will be much larger.

nm/sms (AFP, dpa, Reuters)