Germany is to open an investigation into Opel after claims that the company uses software in two diesel models to manipulate emissions.
After "intense" talks in Berlin, officials said Opel chief executive Karl-Thomas Neumann was unable to debunk results of tests by Der Spiegel magazine.
As a result, federal transport minister Alexander Dobrindt said his officials “had doubts over whether the procedure described is in keeping with motor protection”.
Last week Der Spiegel said tests it carried out on the Opel Astra and Zafira models showed they emitted around 11 times the legal limit of noxious nitrogen oxide
Ope's Mr Neumann was hauled into Berlin’s federal transport ministry on Wednesday to explain reports that software in two models manipulates diesel emissions.
Last week Der Spiegel magazine said tests it carried out on the Opel Astra and Zafira models showed they emitted around 11 times the legal limit of noxious nitrogen-oxide.
The magazine’s investigation, in conjunction with the environmental lobby group DUH, claimed the cars used software to switch off emission filtering above 33 degrees and below 20 degrees.
Denial of claims
Opel has denied claims of widespread manipulation, but has conceded that its diesel filtering only worked fully “in the area of 20 to 30 degrees”.
As Mr Neumann met Berlin officials, the DUH stepped up its claims against Opel. In recent weeks it conducted 19 further on-road tests on an Opel Astra and Zafira. Even above 20 degrees it said the Astra and Zafira emitted 6.6 and 5.5 times the legal limit of nitrogen-oxide respectively.
“I accuse Open chief Neumann of deception towards the authorities and customers,” said Jürgen Resch, chief executive of the DUH.
The organisation demanded a halt to permits for new Astra and Zafiras, and a total recall of all cars already on German roads.
Last September US authorities revealed that VW diesel vehicles were programmed to manipulate emissions, running cleaner when wheels moved with an immobile steering wheel, such as in a test situation.
Opel insists its cars do not run software that detect a test situation, a denial Der Spiegel dismissed as a "smoke grenade" for denying a claim it had not made against Opel.
20 per cent
The magazine says Opel’s temperature controls mean Astras and Zafiras meet emissions limits only around 20 per cent of their time on the road.
A German computer programmer who studied Opel software line by line says it permits full emissions filtering between 17 and 33 degrees, below speeds of 145 km/h or 2,400 revs per minute.
Car emissions tests regulations proscribe test temperatures between 20 degrees and 30 degrees, a maximum speed of 120 km/h and 2,200 revs per minute.
Opel, which declined to provide information for Der Spiegel's tests, said the "isolated findings of a hacker to not reflect the complex interplay of a modern emissions filtering system".
“Test methods and protocols of the activities…were not shared with Opel which does not allow us to evaluate the outcome,” Opel added in statement. “We do not believe that these results are objective or scientifically founded.”
However, the new revelations raise fresh questions about Germany’s level of oversight of its influential car industry.
And, eight months after the VW scandal broke, Berlin faces a legal challenge from a US law firm which claims it broke EU law by failing to act after it was informed about exhaust manipulation.
According to the Süddeutsche Zeitung daily, US attorney Michael Hausfeld has filed a complaint against Germany with the European Commission which could, at worst, end in treaty violation proceedings for Berlin.
