The first large-scale environmental fraud involving DPFs was made possible by massive shortcomings in the approval regulations within the StVZO. This completely dispenses with an effectiveness check of the systems during approval by the KBA. The lack of a practicable short test after installation and the inability of the exhaust emissions test (AU) to detect defective, ineffective or manipulated filters to this day have also provided criminal forces with a huge windfall. Many environmentally conscious diesel owners had to have illegal, ineffective filters replaced with legal ones within a short period of time. This was often at their expense, and at the expense of their workshops.

And what has changed since then? "Nothing!", Steffen Dominsky, editor of "kfz-betrieb", looks back critically: "This is doubly fatal, because the aforementioned StVZO passage could soon be relevant again. Namely when it comes to a hardware solution, i.e. the retrofitting of SCR systems as part of the current diesel scandal."

But the current DPF scandal is much bigger. The role model here - albeit unfortunately a very bad one - is replacement catalytic converters. There is no national or European standard for placing this type of series replacement part on the market - only a lax approval regulation of the United Nations (UN), the UN ECE R103. Manufacturers of replacement catalytic converters can now buy such an approval for a few hundred euros in other EU countries, according to an expert on the subject. And the legal route is also a free ticket for fraudsters. Cat manufacturers can simply submit prepared test samples for homologation. The efficiency of the parts produced later is many times worse. But nobody monitors this afterwards.

The situation with particulate filters is even worse: for a long time, they were not subject to any standard at all. Only since 2011 has ECE R103 also referred to DPFs. However, only very few people know about this. Even spare parts dealers hardly know anything about it and therefore continue to sell products without approval and effect. And those who do know say: "Nobody will notice at the TÜV anyway", which unfortunately proves them right. Because, as in the case of petrol engines, the AU is "blind" in the vast majority of cases - regardless of whether the OBD query or the tailpipe measurement is involved.

But even if one or the other filter now bears a stamp: What applies to catalytic converters in terms of approval also applies to particulate filters. More and more cheap DPFs with an ECE approval mark are coming into circulation, which do not clean the exhaust gas sufficiently. Paradoxically, the newer filter types in particular have to do this. This is because they are usually manufactured as a single unit with the oxidation catalytic converter. As this often contains hardly any of the expensive precious metals required for proper functioning, the connected DPF does not work properly either. As a result, it would quickly become clogged.

In order to avoid exactly this, and the corresponding recourse claims by vehicle owners, unscrupulous manufacturers manufacture their DPFs with holes virtually ex works. These prevent the filter from clogging in the long term. The fact that more than a third of diesel exhaust gases leave the exhaust completely unfiltered does not bother them in the slightest - nor, unfortunately, the legislator.

You can request a reading copy at: pressestelle@vogel.de.

"kfz-betrieb" is the most widely read trade magazine in the automotive industry and has been informing the automotive trade and service sector for over 100 years. "kfz-betrieb" is the official organ of the German automotive trade (ZDK), the professional interest group for around 38,000 car dealerships and workshops. News from the entire automotive industry is available at www.kfz-betrieb.de and in the daily newsletter. The parent company Vogel Business Media is Germany's largest trade media company with 100+ trade journals, 100+ web portals, 100+ business events as well as numerous mobile offerings and international activities. Its headquarters are in Würzburg. The company celebrated its 125th birthday in 2016.