The dispute over temperature-dependent exhaust gas recirculation in diesel engines ("thermal windows") is now also a concern of the European Court of Justice (ECJ).

According to Advocate General Athanasios Rantos, a thermal window can act as a shutdown device and thus violate European law.

In the case of normal conditions of use, the technology reduced the effectiveness of the exhaust gas purification, justified the Advocate General in his Opinion.

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Tobias Piller

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An Austrian court in Luxembourg had presented the original case.

In the Alpine republic, Volkswagen is being sued by customers whose diesel vehicles with the EA 189 scandal engine received a thermal window via a software update.

This only works completely between 15 and 33 degrees outside temperature and only up to an altitude of 1000 meters, argue the plaintiffs.

New billion dollar risk?

Is the auto industry facing the next billion-dollar risk? In any case, Rantos transferred the explanations of an ECJ ruling from December 2020 to the current case. At that time, the European judges declared defeat devices to be inadmissible and restricted the exceptions considerably. The Advocate General made statements about the thermal window for the first time. They are in a certain contradiction to the latest case law of the Federal Court of Justice from last week. In lawsuits against Daimler, Karlsruhe denied that a thermal window per se constitutes compensation for damages. Here the BGH demanded deliberate immoral damage to the customers. 

Even for technicians who have no intention of cheating on environmental supervisors and consumers, coordinating an engine control system with the respective state of the art means weighing up many goals. While the engine of a stationary power generator can always run at the same, optimal speed, a car engine is required to have a minimum speed or maximum power in very different ways under very different temperatures or altitudes. So far, the automotive industry and regulators have assumed that more emissions in extreme situations are of no consequence if the emissions are optimized for the entire vehicle fleet and for most driving situations.

The Advocate General is of the opinion that it is inadmissible if the thermal window only serves to protect the exhaust gas cleaning system itself. However, it was up to the national courts to judge whether this could happen despite regular maintenance of the car, Rantos said. In a statement on the Opinion, VW sees itself confirmed in its technical strategy. The group is of the opinion that overloading the system in “extreme situations”, for example with the exhaust gas recirculation valve (EGR), can lead to unforeseeable damage to the engine itself. These could not be ruled out even with normal maintenance work. VW still considers the thermal window used to be permissible.

On the other hand, it is undisputed that many car manufacturers have chosen the thermal window to be particularly narrow for the optimal functionality and cleaning performance of the engine.

This became apparent when, after the emissions scandal, the Federal Motor Transport Authority (KBA) began to test cars from different manufacturers at temperatures of 5, 10 and 15 degrees outside.

Because the European regulations on the laboratory test on the roller dynamometer, which used to be common, specified a temperature of 20 to 30 degrees.

After the tests, VW was stopped by the KBA to recall many models.

Laboratory tests need to be questioned

With the submission procedure to the ECJ, these laboratory tests are also subsequently subjected to a legal review. Thanks to the definition of many details, they were able to guarantee comparability over a long period of time and across the entire industry. In the recent past, however, all car manufacturers have made efforts to improve the test results through unrealistic optimizations, although hardly anything was felt in practical operation. The WLTP test cycle, which will apply from 2019, also provides for a test in practical road traffic; since 2021, the limit for the laboratory may only be exceeded by 50 percent on the road (Euro 6d).

In Luxembourg, it remains to be seen whether, in the event of a negative decision for VW, not all cars built earlier, for example according to the Euro5 standard (valid from 2011 to 2015), would have to be retrospectively regarded as illegal.

There is also the question of what should happen to other car manufacturers in other countries.

Via Twitter, the German Environmental Aid called on the future federal government to shut down the around 10 million affected diesel frauds with shutdown devices or to have them retrofitted at the expense of the corporations.

"Otherwise we will enforce this in court," threatened Federal Managing Director Jürgen Resch.