As part of a broader investigation into high levels of health-threatening nitrous oxides emissions from diesel vehicles, the German government ordered tests on a broad range of vehicles but found only Volkswagen had installed the sort of illegal manipulation software commonly referred to as a ‘defeat device.’ However, many of the cars tested in ‘real-world’ conditions showed substantially higher emissions than their official lab results suggested.

Dobrindt said the recall, which he called “voluntary”, is to ensure that a legal loophole which allows manufacturers to throttle back emissions treatment systems under certain circumstances is tightened to ensure lower levels of pollution going forward.

Dobrindt was delivering the findings of a controversial parliamentary committee that he convoked immediately after the VW scandal broke in September. Opposition lawmakers have bitterly complained that the commission was working too slowly and in too much secrecy, giving the appearance of being more concerned with protecting the German car industry than with public health and air quality issues. Diesel engines are one of the biggest sources of NOx in European cities, which cause around 75,000 premature deaths a year.

Dobrindt told a press conference that of the 53 modles tested on the road, 27 showed emissions levels only insignificantly above the levels reported in official lab testing. But 22 employed devices that dialed back emissions-cleaning procedures by a conspicuous amount in low temperatures. Although this is allowed by law when needed to protect the engine, Dobrindt said that carmakers “interpret this differently” and suggested had taken liberties.

“If you wanted to exploit the regulation, you could get the most amount of protection for the worst engines, and that can’t be the point,” Dobrindt said.

Recent media reports, and some by official environmental bodies across Europe, have pointed to some engines that initiate such modules in temperatures over 60 degrees–well above the average annual temperature in much of northern Europe.

In a separate development, Daimler AG (DDAIF), the maker of luxury Mercedes-Benz and Smart mini cars, confirmed Thursday that it was investigating its internal testing procedures at the request of the Deparment of Justice. Daimler is facing class action lawsuits in the U.S. from drivers who suspect that its cars may also have slipped through the net of U.S. regulators, but the company has dismissed the suits as “frivolous”.

Separately, Dobrindt also noted that component supplier Robert Bosch & Co., which supplied the software illicitly used by VW, had informed the government that it had also sold the same software to Italy’s Fiat. Bosch has constantly said that its customers alone are responsible for how their product is deployed.