The German Federal Motor Transport Authority (KBA) censored its investigatory reports on the emissions cheating practices of domestic carmakers, the media reported on 31, July.
The KBA already knew over a year ago that Porsche had installed illicit software to falsify the emission levels of its diesel vehicles in test settings, media reports said.
However, the authority delayed the publication of the related information under pressure from the German automotive industry, Xinhua news agency reported.
The KBA is a sub-department of the German Ministry of Transport headed by Alexander Dobrindt (CSU).
In the original and never published report on the nitrogen oxide emission levels of diesel-fueled Porsche Macan models, the KBA had identified an illegal function to reduce emissions levels during test settings.
The software in place must be considered as an "(illicit) defeat device according to regulations", the report said.
After an intervention by Porsche's mother company Volkswagen, the wording was changed to describe the function as being merely a "change to the emissions behaviour of the exhaust system".
In response to the revelations, Green Party (Gruene) politician Oliver Krischer said the correspondence was a clear indication that Transport Minister Dobrindt was aware of Porsche's emissions cheating practices in 2016.
"Back then, the scandal was covered up. Now Dobrindt is attempting to use Porsche as a sacrifice pawn to avoid being associated with the emissions cartel," Krischer said.
The Ministry of Transport did not deny that it had "discussed technical questions" with producers for the "report of the Volkswagen investigatory commission". Such a procedure was "internationally commonplace and necessary", the ministry insisted.
Monday's revelations are the most recent episode of a long-running scandal in which Dobrindt's ministry has been criticised for excessively close ties with German carmakers.
In December 2016, it was shown that the "Volkswagen investigatory commission" had removed sensitive passages from a report into diesel vehicle emissions.
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Updated Date: Jul 31, 2017 20:22:11 IST