BERLIN, Dec. 28 (Xinhua) -- The German ministry of transport revealed details for the retrofitting of old diesel cars on Friday.

According to the regulations, retrofitted diesel cars need to emit less than 270 mg of nitrogen oxides per kilometer in order to be exempted from impending driving bans in Germany.

Transport Minister Andreas Scheuer stated that it would now be "the turn of the retrofitting industry to develop effective systems that comply with all limits and regulations."

Additionally, manufacturers must guarantee that the "system will function properly when used as intended" over a distance of 100,000 km or five years, the ministry stated.

Hardware retrofits of old diesel cars are part of a governmental package to reduce the pollution caused by diesel cars. The German government seeks to prevent driving bans of Euro 4 and Euro 5 emission class diesel vehicles by retrofitting the cars with exhaust gas treatment systems.

Driving bans for older diesel vehicles are currently impending in several German cities due to high air pollution levels. Affected cities are, among others, Frankfurt, Bonn and Essen, where for the first time a section of a German highway could be subject to such a ban. In Hamburg, a driving ban for diesel vehicles has been in force since May.

The German car industry is skeptical about such retrofits of older diesel vehicles. Bernhard Mattes, president of the German Association of the Automotive Industry (VDA), told the newspaper Welt that owners of older diesel vehicles could not rely on the support of German carmakers in case of technical problems after retrofitting their cars.

"We cannot provide a warranty for a vehicle in which third-party exhaust gas cleaning systems have been subsequently installed," Mattes emphasized. "If a customer has his vehicle modified, he and the retrofitter will also be responsible for any possible consequential damage."