Since the stricter measurement method for the exhaust gas test for Euro 6 diesels from July 1, 2023, the failure rate for diesel engines has increased. The particle filters are problematic. The KBA is already investigating Ford. The ADAC suspects problems with the control of the particle filter regeneration.
Since July 1, 2023, Euro 6 diesels have had to undergo a new measurement procedure for emissions testing. As a result, the failure rate for modern diesel engines has risen sharply.
As early as February 2024, the TÜV Association, together with the Central Association of the German Motor Vehicle Industry (ZDK), the ASA Association, Dekra and the KÜS, drew up an initial assessment of the results of the particle counting (PN method) within the framework of the AU.
More kilometers, more problems
The exhaust gas test results of around 950,000 diesel cars in the Euro 6/VI emissions class that were tested by the monitoring organizations between July 1 and October 30, 2023 were evaluated. In the first attempt, around 32,000 vehicles failed the stricter exhaust gas test, which corresponds to a failure rate of 3.43 percent. And the failure rate increases with increasing mileage. For cars with less than 50,000 kilometers on the clock, 2.8 percent failed the exhaust gas test. If the mileage is between 50,000 and 160,000 kilometers, 3.3 percent fail. For cars with more than 160,000 kilometers on the clock, 4.7 percent of the test subjects failed the exhaust gas test. It was noticeable that at the same time only 0.72 percent of the vehicles tested showed a fault in the exhaust system or was stored in the control unit. If one compares the survey with figures from the Federal Highway Research Institute from 2018 to 2020, there is an increase of around 42 percent.
According to the TÜV association, more detailed analyses by brand and model are still being prepared. But all testing organizations already agree that the new particle measurement is necessary in order to detect defects in the exhaust system that would not have been discovered using the old measuring method. Without a passed AU, there is no new HU sticker. Affected vehicle owners must have the exhaust system of their diesel checked and repaired accordingly.
Ford models conspicuous, KBA investigates
According to research by auto motor und sport, Ford diesels in particular are having problems meeting the new standard.
Example: Ursula and Udo Gonsch’s Ford C-Max 1.5 TDCi Titanium only managed to pass the emissions test (AU) in November 2023 with the greatest of effort after three failed attempts. It only worked after installing a new, soot-free exhaust. A new particulate filter, on the other hand, is still not available. The couple now has some breathing room – until the next general inspection (HU) in two years. “We want to sell the car by then,” says Udo Gonsch. Probably with a loss of value because of the “black box particulate filter”. The TÜV debacle came without warning. In all previous general inspections, the C-Max had easily passed the AU hurdle.
The particle problem has also hit Yvonne Schneider hard. The single mother from Cologne is dependent on her car. In part because the 43-year-old has to regularly drive a cousin who is paralyzed on one side to therapy. But her 2016 Fiesta 1.5 TDCi has been standing still for five months and a new particle filter is not available. The city employee does not want to get behind the wheel without an MOT, especially since in the worst case scenario she could face fines of up to 60 euros and a point on her license. She had even bought a new car eight years ago: “I wanted peace of mind from major repairs.”
Remarkable: Yvonne Schneider’s Fiesta did not pass the exhaust gas test on the first attempt in 2019 and 2021, when the less strict turbidity measurement still applied. Only regeneration drives helped the small car overcome the exhaust gas hurdles at the time.
According to information from a testing organization to auto motor und sport, seven models from the Cologne manufacturer are among the top 15 vehicles that failed. A large company for particle filter cleaning confirms: Almost half of all vehicles whose diesel particle filters (DPF) are currently being sent in for cleaning because they failed the emissions test are Ford models. According to the ADAC, it is primarily cars with the 1.5-liter TDCi diesel that fail the emissions test. Even before the emissions test changeover in July 2023, the Federal Motor Transport Authority initiated market surveillance proceedings against Ford. The testers want to know whether the DPFs meet durability requirements or whether there is a series defect.
The problem may be in the control system
In the meantime, the ADAC, in collaboration with auto motor und sport, has examined two particulate filters from Ford models that had failed the main inspection due to excessive particle emissions. During the investigation, however, the ADAC was unable to find any obvious faults in the filters.
The ADAC believes it is possible that the excessive particle emissions are not due to the filter itself, but that the active and passive regeneration of the filters is not controlled correctly. Passive regeneration takes place during normal driving under favorable conditions. The soot then burns off below operating temperature. Active regeneration occurs, among other things, when the filter has reached a certain fill level. Higher temperatures are required to burn the larger amount of soot, which is then generated by additional fuel injections. If the filter does not clean properly, it can no longer filter out enough particles from the exhaust gas.
When asked by auto motor und sport, Ford did not comment on the ADAC’s suspicion that the problem might be caused not by the filters themselves but by faulty filter control by the vehicle’s electronics. According to the Federal Motor Transport Authority (KBA), the investigations into the filter problems are nearing completion. The KBA has checked whether the diesel particulate filters installed by Ford meet the durability requirements or whether there is a series defect. If such a defect exists, the KBA could initiate a recall.
Particle filters are rare and expensive
In addition to the popular 1.5 TDCi, the 2.0 EcoBlue is also affected, according to Ford. Winemaker Peter Kollmann from Schleich on the Moselle drives a Transit Custom with this engine. Mostly on long-distance routes to deliver wine all over Germany. In an exhaust gas measurement in September 2023, the van was more than twenty times above the limit of 250,000 particles per cubic centimeter of exhaust gas. A filter was not available until November 2023 – for around 2,100 euros including installation. Kollmann is now demanding the costs back from Ford – including loss of earnings. “I think it’s unfair what happened to me. With almost 60,000 kilometers, it’s an almost new car.”
What worries the winemaker: During the exhaust gas inspection with the new DPF, the car reached a maximum particle count of 109,400. That was enough to pass, but: A sample taken by GTÜ and auto motor und sport on a new Golf GTD showed a value of just 7,223. Fault-free exhaust gas purifiers can achieve measured values of less than 10,000. Kollmann fears that the particle count could continue to rise by the next exhaust gas inspection in November 2025.
The fact that this could be a nail-biter is evident from the tailpipe of his Transit Custom, which is already pitch black. An indication that something could be wrong again.
According to Barten from Wegberg, which has been processing DPFs for more than 20 years, in addition to the poor quality of a new filter, soot deposits in the rear silencer or decomposing filler wool can also be responsible for excessively high particle levels. Contamination of the SCR catalyst by soot and AdBlue deposits is also conceivable. “In many cases, defects in the engine periphery and faulty regeneration lead to premature overloading and even damage to the filter,” says spokeswoman Sabrina Konijnenburg.
She advises not to drive to have the exhaust gases measured while the filter is being regenerated or shortly after starting the engine. “In both cases, emissions are often higher.” Defective filters should be replaced with original manufacturer parts that meet the Euro 6 standard. It must be ensured that the entire exhaust system is clean.
Other brands also affected
The particle problem also affects other brands in some cases. Thomas Rauh from Bad Wimpfen near Heilbronn is actually very happy with his Volvo V60 D3 from 2017. But the station wagon also failed the last MOT in February with a good 1.76 million particles. Rauh has been waiting for a new filter ever since. Expected delivery date: July 2024. A goodwill request was initially rejected. When auto motor und sport asked Volvo, a spokesperson announced that they wanted to install the filter “at no cost”.
The diesel drama was not announced in advance: “No warning light reported the defective filter, consumption did not increase, and the engine continued to run smoothly,” says Rauh. This is also confirmed by the TÜV Association’s survey. The particle problem was only displayed in the cockpit of 29 percent of the cars that failed the test. “The new measuring technology offers considerable potential for improvement in the goals of air pollution control, because we can now identify faulty exhaust gas purification systems much better,” says Marco Oehler, technical director of GTÜ.
Until the end of 2017, the emissions test could even be carried out entirely via the vehicle’s own diagnostic system (OBD). If nothing was found during the reading at that time, the tailpipe measurement could even be dispensed with entirely.
Karl Stechhammer also never received any indication that there was something wrong with his nine-year-old Mercedes ML 350 Bluetec – until the MOT appointment on November 5, 2023. “Failed” was the inspectors’ verdict. The pensioner from Markt Berolzheim in Franconia has been waiting for a new particulate filter for six months. He also doesn’t want to drive without an MOT, especially abroad, it’s too risky for him. “I’ve already canceled two vacations because of this,” says Stechhammer, “I don’t see why I should stand still with a luxury SUV.” What’s particularly annoying is that suitable DPFs are available on the open market. But according to the workshop information, his extended warranty only covers the installation of original Mercedes parts.
Particles are becoming finer
But why did so many Euro 6 diesels pass the old test method without any problems, but are now failing with flying colors? For Marco Oehler from GTÜ, there is one main reason for this: “In modern diesel engines, the particles are burned so finely through optimized combustion and high temperatures that they produce a cloudiness that is barely measurable for the previous method.”
According to filter reconditioner Barten, TÜV and Co. were only able to use the turbidity measurement to determine whether a DPF had failed completely, but not how effectively it was still working.
That is different now, says Barten spokeswoman Konijnenburg: “We are observing that an increasing number of vehicles from the brands Ford, Opel, Volvo and Mercedes have not passed the emission tests.” This also applies to “those that are affected by software updates, cheating software or recalls for EGR coolers.”
Different approaches to the problem are possible
A theory that has not yet been proven: the diesel particle filters of some manufacturers could be designed in such a way that they only last a long time in conjunction with switch-off devices. If these are removed via a mandatory update by the manufacturer, the filter could become clogged more quickly. This could be consistent with the fact that manufacturers often justify so-called thermal windows before the European Court of Justice by saying that they want to protect the particle filter, among other things.
Other explanations for failure of the exhaust gas test are also conceivable. For example, the DPF regeneration starts on the way to the emissions test because after a long time the usual short-distance driving profile is finally being deviated from. The filter uses this opportunity to clean itself – just at the wrong time, which can spoil the exhaust gas test result.
It is also conceivable that the ceramic monolith is of inferior quality or has been designed to be very porous in order to offer little resistance to the exhaust gas flow. This would reduce consumption but would allow too many particles to pass through. Ford says the main cause of the emissions problems is “a malfunction of the diesel particulate filter due to high temperatures”.
No guarantee or warranty claims – maximum goodwill
From a legal perspective, there are hardly any ways out of the filter trap. According to the ADAC, there are generally no guarantees or warranty claims against the vehicle manufacturer. Up to a maximum of two years after the purchase, there may still be claims for liability for material defects against the seller. According to the automobile club, claims for damages are also ruled out. At best, goodwill could help.
And what do Ford, Mercedes and Volvo say about the allegations?
Ford speaks of “some vehicles built between 2014 and 2023” with 1.5 TDCi and 2.0 EcoBlue engines that were affected by “a malfunction of the diesel particulate filter due to high temperatures” and therefore had not passed the AU since July 2023. The cause is being investigated and is “in close contact with the Federal Motor Transport Authority”. In 2021, “the new test method was initiated by the Association of Filter Manufacturers”. “Like the entire industry”, Ford is affected by “supply bottlenecks for the particulate filters to be replaced”. Dealers can provide rental cars, and in individual cases there is goodwill. According to Ford, all vehicles meet “all legal limits in homologation as well as in conformity and in-service tests”.
Mercedes points out that the DPF is a wear part, which “in individual cases can lead to an increased number of particles in the exhaust gas measurement”. As a rule, Mercedes filters pass the exhaust emission test without any problems. There is “no known unusually high error rate” for these, not even for specific series. However, “supply bottlenecks in the supply chain” are currently limiting the availability of replacements.
A Volvo spokesperson could not say whether the Volvo V60 has a series defect. The reason for the long delivery time for the replacement filter is a change of supplier. The DPF for Thomas Rauh’s V60 is to be replaced “at no cost”.
Old test standard for old diesel
The less strict turbidity measurement continues to apply to diesels of standards 5 and below. According to the Federal Ministry of Transport, “according to EU law, no stricter requirements may be applied than those that applied at the time of EU type approval of the vehicles.” At that time, there were no uniform particle number limits for Euro 5 diesels. “Particle number concentration measurement was only introduced in Germany for the Euro 6 emissions class,” said a spokeswoman. According to the ministry, the new measurement method cannot be used for direct-injection gasoline engines. The reason: the new PN measurement takes place when the engine is idling. Gasoline particle filters, however, primarily work at high engine loads or after a cold start. In addition, gasoline particles are too small for the new measurement.
How can defective filters be identified?
There is a rough rule of thumb for the lifespan of diesel particle filters (DPF): depending on the driving profile and model, between 120,000 and 240,000 kilometers. A sign of a broken DPF can be heavily sooted exhaust tailpipes. Alternatively, a handkerchief can be held against the opening while the engine is running. If it turns black, the DPF is usually mechanically defective.
Although MOT and AU are due every two years, some car manufacturers only give a one-year guarantee on retrofitted filters. If the above-mentioned signs are present, it may be advisable to have an exhaust gas test carried out before the guarantee expires.
If a replacement DPF is not available or too expensive, a reconditioning (starting at around 350 euros) can help. Depending on the car brand, the chance of success is up to 50 percent. “If it’s just the particulate filter, we can help. If the engine is broken, even the best filter is of no use,” says Matthias Pethke from the reconditioning company Pethke Metall.
Mirco Ortlieb from particle filter specialist Greencar advises: “After cleaning, do not immediately go for an emissions test, but first run the new filter in for around 400 kilometers.”
Conclusion
Since July 2023, there has been a new measurement method for Euro 6 diesels in the exhaust gas test. According to an initial interim report from the testing organizations, more diesel vehicles have tended to fail the test since then. The particle filters or other parts of the exhaust system cause problems. Since these are considered wearing parts, the affected vehicle owners are usually left with the costs.
Source: Auto Motor Und Sport