Volkswagen’s own staff and one of its suppliers warned years ago about software designed to thwart emissions tests, two German newspapers reported yesterday, as the automaker tries to uncover how long its executives knew about the cheating.

The world’s biggest automaker is adding up the cost to its business and reputation of the biggest scandal in its 78-year history, having acknowledged installing software in diesel engines designed to hide their emissions of toxic gasses.

Countries around the world have launched their own investigations after the company was caught cheating on tests in the United States. Volkswagen says the software affected engines in 11 million cars, most of which were sold in Europe.

The company’s internal investigation is likely to focus on how far up the chain of command were executives who were responsible for the cheating, and how long were they aware of it.

The Frankfurter Allgemeine Sonntagszeitung, citing a source on VW’s supervisory board, said the board had received an internal report at its meeting on Friday showing VW technicians had warned about illegal emissions practices in 2011. No explanation was given as to why the matter was not addressed then.

Separately, Bild am Sonntag newspaper said VW’s internal probe had turned up a letter from parts supplier Bosch written in 2007 that also warned against the possible illegal use of Bosch-supplied software technology. The paper did not cite a source for its report. Volkswagen declined to comment on the details of either newspaper report.

“There are serious investigations under way and the focus is now also on technical solutions” for customers and dealers, a Volkswagen spokesman said. “As soon as we have reliable facts we will be able to give answers.”

A spokesman for Bosch said the company’s dealings with VW were confidential. Bild said Martin Winterkorn, who quit as Volkswagen CEO last week, was demanding his salary for the rest of his contract through the end of next year but the board did not want to pay it. It cited no source. Winterkorn was paid €16 million last year, the most of any CEO in Germany’s blue chip DAX index.

The scandal must not be allowed to tarnish the ‘made in Germany’ brand

Volkswagen is still coming up with plans to deal with the 11 million cars that it built with the affected engines. Its Italian unit has told its dealers to stop selling them, Italy’s Corriera della Sera newspaper reported yesterday.

It said that would leave 40,000 cars stuck on Italian lots. A Volkswagen spokesman said there had been no instructions from company headquarters in Germany to dealers to stop selling the affected cars, but sales units in individual countries had the right to take such decisions on their own.

In Volkswagen’s home market Germany, where 2.8 million of the 11 million affected diesel cars are on the road, the government watchdog KBA has set an October 7 deadline for the company to present a plan to bring diesel emissions into line with the law, Bild reported.

German politicians have been adding to the pressure on Volkswagen, worried about the reputation of German industry.

“We need a guarantee that cars of German manufacturers are in line with the norms, without manipulation,” Chancellor Angela Merkel’s chief of staff Peter Altmaier told Der Tagesspiegel in an interview published yesterday.

Environment Minister Barbara Hendricks said the scandal must not be allowed to tarnish “the made in Germany brand”.

“If a global player from Germany violates environment protection rules that blatantly, this casts a shadow on the environment pledges of German companies,” she said. She said the EU was working on stricter emissions tests to focus more on normal road conditions, rather than rely on lab results.

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