VW was warned years ago about the use of software designed to manipulate emissions tests, German newspapers report.

According to Frankfurter Allgemeine Sonntagszeitung, which cited a source on VW’s supervisory board, VW technicians had warned about illegal emissions practices in 2011. However, no explanation was given as to why the matter was not addressed then.

In a separate report, Bild am Sonntag said VW’s internal investigation found a letter from parts supplier Bosch written in 2007. The letter also warned against the possible illegal use of the software technology supplied by Bosch.

Volkswagen said it is currently focusing on finding technical solutions for customers and dealers. “There are serious investigations underway and the focus is now also on technical solutions” for customers and dealers, a Volkswagen spokesman was quoted as saying by Reuters. “As soon as we have reliable facts we will be able to give answers,” the representative added.

As for Bosch, a company spokesman said the company’s discussions with VW were confidential.

Last week, Bosch confirmed it had delivered components to VW that are now at the center of a probe into rigged emissions tests. Among the components there were delivery and metering modules for exhaust gas treatment and common-rail injection systems.

According to Bild am Sonntag, everything started in 2005 when VW brand chief Wolfgang Bernhard wanted VW to build a new diesel engine for the US market. The only way to make the engine meet US emissions standards was to fit it with an AdBlue urea solution used on larger diesel models such as the Passat and Touareg.

However, that would have added a cost of €300 per vehicle and was not approved by VW finance officials. Bernhard left VW in January 2007 before the diesel engine went into production.

When Martin Winterkorn became VW Group and brand CEO in 2007, he asked Audi development boss Ulrich Hackenberg and Audi engine boss Wolfgang Hatz to move to VW’s Wolfsburg headquarters and continue development work on the engine.

The engine then ended up in VW Group models with its software manipulated to fool diesel emissions tests in the United States.

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