Volkswagen CEO Matthias Mueller at the 2017 Frankfurt Motor Show (IAA) in Germany. Photo: Reuters

Volkswagen’s CEO said he was “stunned” by reports the carmaker had sponsored tests that exposed monkeys and humans to toxic diesel fumes and, two years after an emissions cheating scandal, pledged once again to get to the bottom of the wrongdoing.

Europe’s largest automaker has come under fresh scrutiny after the New York Times said last week that Volkswagen and German peers BMW and Daimler funded an organisation called European Research Group on Environment and Health in the Transport Sector (EUGT) to commission the tests.

The report came more than two years after Volkswagen admitted to cheating US diesel emissions tests, sparking the biggest business crisis in its history and pledged sweeping changes to ensure such misconduct never happened again.

Over the weekend we had to learn once more that there is still a long way ahead of us to regain lost trust,” VW CEO Matthias Mueller said at a reception in Brussels late yesterday, in his first public remarks on the tests.

“The methods used by EUGT in the US were wrong, they were unethical and repulsive,” he said. “I am sorry that Volkswagen was involved in the matter as one of the sponsors of EUGT.”

The study, conducted in 2014, was designed to defend diesel following revelations that the fuel’s exhaust fumes were carcinogenic, the New York Times reported.

Reuters could not confirm the details and purpose of the study and EUGT, which was dissolved last year, could not be reached for comment. BMW and Daimler have also denounced the tests.

Mueller, a company veteran who become CEO after the emissions test cheating scandal broke in September 2015, has complained on several occasions that tackling VW’s closed-off corporate culture was proving tougher than expected.

He said the New York Times report showed VW had to raise its game in improving ethical standards and pledged to take the necessary action once it had finished investigating EUGT’s work.

“We must live and deal with setbacks,” he said.

VW said yesterday the EUGT study was never discussed in any management board meetings, after the Bild newspaper earlier reported an internal e-mail showed at least some senior managers were informed about the design of the research.

The study risks dealing another blow to diesel technology, in which the German auto industry has invested heavily.