On Tuesday Volkswagen, which is Europe's largest car manufacturer, fired its chief lobbyist who knew in advance about the test that has so shocked Germany.
German environment minister Barbara Hendricks, who was in Brussels on Tuesday to discuss measures to improve air quality in badly polluted cities, called the tests "irresponsible".
"It is once again astonishing that there are companies in the auto sector who are unaware of the responsibility of their behaviour," she said.
Two years ago the company was caught doctoring software in its diesel cars to produce false data to pass emissions tests.
The German car industry has invested heavily in diesel technology and the test - carried out in 2014 - was designed to investigate reports that diesel fumes are carcinogenic.
Two years before the World Health Organisation had stated that diesel fumes do in fact cause lung cancer.