The measurement of particle concentration (PN measurement) during vehicle emissions testing (AU) is showing results from the perspective of the TÜV Association. Since July 2023, a new measurement method has been applied directly at the exhaust tailpipe for cars and trucks with diesel engines starting from the Euro 6/VI emission class to determine the harmful fine dust concentration in the exhaust gases. In 2024, almost 4.5 million diesel vehicles in Germany in the Euro 6/VI emission class were tested. 3.0 percent did not pass the emissions test on the first try. In absolute numbers, this corresponds to around 132,600 vehicles. This is the result of a joint analysis by the TÜV testing organizations as well as DEKRA, GTÜ, KÜS, and the recognized AU workshops.
“With particle measurement, vehicles with defective or manipulated exhaust systems are reliably detected and removed from circulation. The PN measurement contributes to improving air quality and
thus makes an important contribution to health, the environment, and climate,” explains Robin Zalwert, consultant for sustainable mobility at the TÜV Association.
Defects such as defective diesel particulate filters or faulty sensors must be corrected within four weeks, and the vehicle must be presented again. It is particularly important that so-called “gross polluters” are identified during the emissions tests. Studies have shown that a gross polluter percentage of only five percent of the vehicle fleet can be responsible for about a quarter of all traffic-related pollutant emissions.
Defect rates in the exhaust system increase with age
According to the evaluation results, the defect rate in emissions testing increases with the age of the vehicles. For vehicles under 5 years old, it is 2.0 percent; for vehicles 5 to 10 years old, it is 4.0 percent, and for vehicles older than 10 years, it is 6.1 percent, far above the average.
“In the coming years, the currently still small proportion of older Euro 6 vehicles will steadily increase,” predicts Zalwert.
According to the Federal Motor Transport Authority (KBA), the average age of cars in Germany is steadily increasing and is currently 10.6 years. “Owners of older cars are urged to invest in the maintenance of their vehicles while keeping an eye on the exhaust systems,” says Zalwert. “Otherwise, there is a risk that the vehicle will fail the main inspection and emissions test.”
The expert positively assesses that commercial vehicles with a permissible total weight of more than 3.5 tons have a defect rate of 2.2 percent below the average. “This speaks for an overall good condition of the truck fleet in Germany, which results from a combination of regular maintenance and independent inspections,” says Zalwert.
Many defects remain undetected without tailpipe measurement
The analysis of the emissions tests has shown
that only about one-third of the defects identified during the tailpipe measurement would also have been discovered with the electronic vehicle diagnostic system. Two-thirds of the defects would have remained undetected with a purely on-board diagnosis (OBD). Before the introduction of the new measurement method, there was an intensive discussion about the usefulness of tailpipe measurement. Critics thought the OBD was sufficient.
“The PN measurement at the tailpipe has impressively demonstrated its effectiveness,” says Zalwert.
From the perspective of the TÜV Association and other testing organizations, particle measurement is a successful model that should be extended to other emission classes. In particular, diesel vehicles of the Euro 5b emission class are suitable candidates. Zalwert believes: “In this vehicle group, it is assumed that there are still many highly emitting diesel vehicles on the road. The introduction of a PN measurement here would be a consistent and effective step towards further
