While they mention auditing suppliers (p. 65), their disclosure on conflict minerals gives the impression that their due diligence on their mineral supply chains is pretty much none existant.
"Due to international crises, certain regions of the world are exposed to the risk that armed conflicts could be financed with the revenues from the sale of raw materials. In order to prevent conflicts arising from the trade with so-called conflict minerals (tin, tantalum, tungsten, and gold), a series of initiatives have been introduced aiming at a declaration of the origin and the responsible procurement of the raw materials.
For example, Section 1502 of the US Dodd-Frank Act stipulates that companies listed on US stock exchanges must certify the source of these commodities along the entire supply chain. In Europe, the European Union also envisages legislation on this matter. Daimler supports an approach for the establishment of responsible procurement of raw materials that is both purposeful and practicable, and engages in regular dialog with industry associations such as the German Association of the Automotive Industry." p. 65