The German government is under pressure to explain its alleged collusion with auto giant Volkswagen to cheat CO2 emissions tests. According to Transport Ministry documents leaked to "Stern" magazine, VW worked together with the ministry to defuse an impending CO2 emissions scandal in 2015, only months after the US Environmental Protection Agency found that VW was using special software to cheat NOx emissions tests.

In November 2015, VW CEO Matthias Müller admitted publicly that company employees had lowered CO2 emissions figures for 800,000 vehicles. But a month later, VW revised that figure following "thorough internal tests and measurement checks," and decided that only 36,000 cars showed discrepancies between lab tests and road reality.

In between, "Stern" reported, VW sent two lawyers to the Transport Ministry to inform the government that the car-maker was changing its position. VW would no longer blame its own employees, a leaked transcript from that November meeting recorded, but from now on the company would say "that up to now it could not be decided what reasons lay behind the too-high CO2 figures."

Not only that, VW told the ministry that it was backtracking on a previous internal pledge to measure emissions according to "tougher standards." According to the transcript, the ministry officials "took note of this consentingly." The ministry has not responded to requests for comment either to "Stern" or DW.

Widening gap

Jens Hilgenberg, transport emissions specialist at environmental group BUND, wasn't surprised that the German government did not censure one of the country's biggest companies - "but we didn't know that they would do it so bluntly," he told DW. "That they would tell VW: 'you can just take back the measurements you've carried out yourself'."

Hilgenberg explained that it had long been clear that both VW and the government must have been aware of the CO2 levels once they'd measured NOx levels in response to the VW scandal. "If you measure NOx then you also automatically measure CO2," he said. "You can't not do it."

BUND is among several environmental groups to have asked the government to release its CO2 emission test results carried out by the Federal Motor Transport Authority (KBA), but has always been refused on the grounds that the tests are still ongoing. Some of the KBA's results were leaked to "Stern," and showed that in 14 models - including Mercedes, Opel and Porsche cars - the gap between lab tests and road reality was over 10 percent.

It has long been clear that there is a huge disparity between the amount of CO2 an average car releases in a lab test and on the road - but that gap is getting wider and wider. An International Council on Clean Transportation (ICCT) study released on Wednesday found that "in the EU, the gap between official and real-world CO2 emission values continues to grow - from 9 percent in 2001 to 42 percent in 2015."

This has a significant financial impact - both on consumers and the public purse. The ICCT estimates the hidden fuel inefficiency is costing motorists an extra 450 euros ($480) a year, and since tax incentive schemes for low-carbon cars are based on official CO2 values rather than real ones, "the gap may also lead to significant losses of tax revenue and a misallocation of public funds." The German environmental group DUH estimates that this will cost the state 2.2 billion euros this year.

So easy to cheat tests

Oversight and emissions testing are so poor that there is barely any need to resort to special software to cheat lab tests. "They put very narrow tires on the cars with no tread to create as little friction as possible. The tires have triple the air pressure in them," said Hilgenberg. "If you actually drove a car like the one they put on the test bed you'd crash into a tree after a hundred meters. A car like that wouldn't even be allowed on the road." It's only on road tests like those used in the US, in fact, when the cheat software becomes necessary, said Hilgenberg.

On top of that, there is hardly any capacity for independent emissions testing in Germany. "The KBA doesn't have a test bed - there are one or two in universities, but they work very closely together with the auto industry," said Hilgenberg.

"The manufacturers have always used every trick and gray area - legal or not - to manipulate the official CO2 value of their cars," said Hilgenberg. But even with this routine manipulation, the situation has changed so drastically in the past ten years that it is effectively impossible for most people to drive a car carefully enough to meet its official CO2 levels. In other words, consumers are being tricked by carmakers.

The problem, according to BUND, is not the levels themselves, but the fact that many manufacturers - especially German ones - have failed to keep up with new developments in fuel-saving hybrid technology. "Look at Toyota," said Hilgenberg. "They meet the standards easily."