A thermal window that reduces exhaust gas cleaning in diesel vehicles at normal temperatures is not permitted.

The European Court of Justice (ECJ) said on Thursday in Luxembourg that an exception could apply if it can be proven to protect against serious risks for the engine that pose a danger when driving.

Even then, such a defeat device would not be permitted if it mostly had to run under normal conditions.

(Az. C-128/20 and others)

For exhaust gas cleaning in diesel, some of the exhaust gases are fed back into the engine and burned again.

With the thermal window, this is reduced or stopped when the outside temperatures are particularly warm and, above all, cooler, which is why the vehicles then emit more nitrogen oxides.

The cases at the ECJ concerned lawsuits from Austria against Volkswagen and two car dealers.

The car buyers demanded the purchase price back.

The Austrian courts dealing with the cases asked the ECJ whether the thermal window was permissible.

However, its assessment is also binding for other national courts, which is why it can affect cases throughout the EU.

The Austrian courts must now examine whether the thermal window was necessary to protect the engine in the specific cases and whether there was no other solution.

Both sides see themselves confirmed

They assumed that the low-emission mode was only guaranteed when the outside temperature was between 15 and 33 degrees Celsius and at an altitude of less than 1000 meters.

Volkswagen asserted before the ECJ that it was about the charge air temperature in the engine, which was higher on average.

However, the ECJ has now declared that the referring national court alone is responsible for assessing the facts of the case.

If compliance with the emission limit values ​​was only guaranteed at an outside temperature between 15 and 33 degrees and below 1000 meters in altitude, it would be a defeat device.

He also pointed out that lower temperatures are normal in the EU and the exhaust gas limits must be observed even then.

Even if a defeat device serves to protect against sudden dangers but has to function for most of the year under normal operating conditions, this is not permissible.

Otherwise, the exception could be applied more frequently than the ban, the ECJ explained.

He did not rule out a refund of the purchase price.

However, the national courts must decide on this in individual cases.

After the decision, the car manufacturer Volkswagen stated that it saw its legal opinion confirmed: "According to the criteria set out by the ECJ in its judgment, the thermal windows used in vehicles of the VW Group remain permissible." They protect against immediate risks for the driver Engine in the form of damage or accident.

The chairman of the Austrian consumer protection association, Peter Kolba, said: "This puts an end to the arguments of diesel manufacturers and German authorities that these thermal windows serve to protect the engine and are therefore legal."

The German Federal Motor Transport Authority had approved software updates with thermal windows.

The updates were installed by Volkswagen, among other things, to fix the illegal manipulations in the diesel scandal.

In fact, most car manufacturers use thermal windows.

The Federal Court of Justice in Germany has so far rejected claims for damages by vehicle buyers solely because of the thermal window.