Therein lies the rub. German testing organization TÜV Hessen has been testing aftermarket particulate filters and the results aren't good. Some of the filters made by Bosal, Tenneco and GAT removed only from zero to ten percent of soot. The filters are now being re-tested, but in the meantime installers are at a stand still. The manufacturers have already pulled some of the disputed units off the market. It's expected that the market for aftermarket particulate filters in Germany could hit 1.5 million units in the next two years.
[Source: Automotive News - Sub. req'd]