Was ist ein Thermofenster genau?

Ein Thermofenster ist eine Softwarefunktion, die die Abgasrückführung (AGR) oder andere Abgasreinigungssysteme in Abhängigkeit von der Außentemperatur reguliert. Bei Temperaturen außerhalb eines definierten Bereichs – typischerweise unterhalb von 10 bis 15 Grad oder oberhalb von 30 bis 35 Grad – wird die Reinigungsleistung reduziert oder ganz abgeschaltet. Das Fahrzeug erfüllt die Emissionsgrenzwerte dann nur noch auf dem Prüfstand, nicht im realen Fahrbetrieb.

Was hat das EuGH-Urteil 2023 für mich als Fahrzeughalter konkret verändert?

Das EuGH-Urteil C-100/21 hat klargestellt, dass nationale Gerichte Schadensersatz zusprechen müssen, wenn eine unzulässige Abschalteinrichtung vorliegt – auch ohne Nachweis von Arglist oder Vorsatz. Das war nach bisheriger BGH-Rechtsprechung die größte Hürde für Kläger. Jetzt reicht der Nachweis der unzulässigen Einrichtung aus.

Habe ich Ansprüche, obwohl ich das Auto nicht neu gekauft habe?

Ja. Der Schadensersatzanspruch richtet sich gegen den Hersteller (Deliktshaftung), nicht gegen den Händler. Er gilt für Erst- und Zweitkäufer gleichermaßen, sofern der Schaden – also der Erwerb eines mangelbehafteten Fahrzeugs zu überhöhtem Preis – beim konkreten Kauf entstanden ist.

Welche Schadensersatzsumme kann ich erwarten?

Beim kleinen Schadensersatz sind nach aktueller BGH-Rechtsprechung 5 bis 15 Prozent des Kaufpreises realistisch. Bei einem Kaufpreis von 40.000 Euro bedeutet das 2.000 bis 6.000 Euro Schadensersatz. Beim großen Schadensersatz hängt die Erstattung vom Kaufpreis und den gefahrenen Kilometern ab. Rogert & Ulbrich schätzt Ihren konkreten Fall individuell ein.

Gilt das Thermofenster-Urteil auch für andere Hersteller als VW?

Ja. Das EuGH-Urteil C-100/21 betraf Mercedes-Benz, gilt aber als Präzedenzfall für alle Hersteller. Gerichte wenden die Grundsätze auf BMW, Opel, Fiat und andere Hersteller mit vergleichbaren Thermofenstern an. Die Verfahren laufen branchenweit.

Was ist der Unterschied zwischen dem Dieselskandal und dem Thermofenster?

Im ursprünglichen Dieselskandal (ab 2015) setzte VW eine Software ein, die den Prüfstand aktiv erkannte und nur dann im Normalmodus fuhr. Das war offensichtliche Manipulation. Das Thermofenster ist subtiler: Es reduziert die Abgasreinigung unter bestimmten Außenbedingungen, die in realen Fahrsituationen häufig auftreten. Hersteller argumentierten lange, das sei technisch notwendig – eine Argumentation, die der EuGH weitgehend zurückgewiesen hat.

Ist mein Fahrzeug von einem Software-Update betroffen?

Viele Hersteller haben nach behördlichem Druck Software-Updates angeboten, die das Thermofenster anpassen. Solche Updates beseitigen jedoch nicht automatisch Ihre Schadensersatzansprüche für die Vergangenheit. Der Schaden ist bereits beim Kauf des mangelbehafteten Fahrzeugs entstanden.

Was passiert, wenn ich das Fahrzeug bereits verkauft habe?

Auch wenn Sie das betroffene Fahrzeug bereits veräußert haben, können Schadensersatzansprüche bestehen – sofern die Verjährung noch nicht eingetreten ist. Der Schaden entstand beim Kauf des Fahrzeugs zu einem Preis, der den Mangel nicht berücksichtigte. Rogert & Ulbrich prüft die Verjährungslage in Ihrem Fall.

Wann sollte ich einen Anwalt einschalten?

Baldmöglichst, da Verjährungsfristen laufen. Bei Fahrzeugen, deren Thermofenster erst durch das EuGH-Urteil 2023 rechtlich klar eingestuft wurden, beginnt die Verjährung mit Ablauf des Jahres 2023. Die Dreijahresfrist läuft damit Ende 2026 ab. Rogert & Ulbrich prüft, ob Ihr Fahrzeug betroffen ist, und leitet entsprechende Schritte ein. Viele Mandate werden über eine Rechtsschutzversicherung abgewickelt.

Thermal windows in the emissions scandal – compensation and your claims
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What a thermal window is, why it is legally relevant, and how vehicle owners can enforce compensation claims.

Following the initial diesel scandal involving manipulated test bench software, the thermal window is the central issue in the second wave of the emissions scandal. Almost all major car manufacturers are affected – including Volkswagen, Audi, Mercedes-Benz, BMW, Opel, and Fiat. Rogert & Ulbrich represents vehicle owners against manufacturers who have used thermal windows as illegal defeat devices and enforces claims for damages in court.

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What is a thermal window?
Technical explanation

A thermal window is a software function in the engine control unit that regulates exhaust gas purification – especially exhaust gas recirculation (EGR) – depending on the outside temperature. Within a specific temperature range, the so-called "window," the exhaust gas purification system operates fully. Outside this window – in cold or hot conditions – the purification performance is reduced or deactivated.

In practice, this means that on the test bench, which is conducted under controlled conditions at around 20 to 30 degrees Celsius, the vehicles meet the emission limits. In real-world driving conditions, where temperatures can be significantly lower or higher, they considerably exceed the limits for nitrogen oxides (NOx).

Manufacturers often justify thermal windows by claiming they protect the engine from wear or damage – a justification that is increasingly viewed critically by European courts when the window is defined so narrowly that it excludes the vast majority of real-world driving conditions.

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Illegal defeat device or legitimate engine protection?
Legal classification

The legal classification of the thermal window is the core conflict in thousands of legal cases. EU Regulation 715/2007 prohibits the use of defeat devices that reduce the effectiveness of emission control systems. Exceptions are only permitted if the device is necessary to protect the engine from sudden and unexpected damage.

In a landmark ruling in September 2023 (C-100/21, Mercedes-Benz), the European Court of Justice (ECJ) clarified that defeat devices that reduce exhaust gas purification outside of narrowly defined exceptions are inadmissible. A thermal window that reduces EGR at temperatures below 15 degrees Celsius or above 33 degrees Celsius does not cover the normal operating range of a vehicle and is therefore not covered by the exemption.

Crucially, the ECJ ruling also clarified that vehicle buyers have an individual right to compensation in cases of illegal defeat devices – even if they do not have to prove fraudulent intent on the part of the manufacturer. This is a significant difference from previous German case law, which often required proof of fraudulent intent.

Federal Court of Justice (BGH) case law on thermal windows
the long road to clarity

The Federal Court of Justice (BGH) has addressed the issue of thermal windows in several rulings. Until 2023, the BGH predominantly rejected claims for damages related to simple thermal windows, because it did not find evidence of intentional and immoral harm (§ 826 BGB) – the earlier basis for the diesel rulings.

The ECJ ruling of September 2023 fundamentally changed the legal situation. The ECJ ruled that national courts must award damages as soon as an illegal defeat device is present – proof of fault is not required. The German Federal Court of Justice (BGH) must take these European legal requirements into account.

Following the ECJ ruling, German courts have increasingly awarded damages for thermal windows. With its ruling of June 26, 2023 (VIa ZR 335/21) and subsequent decisions, the German Federal Court of Justice (BGH) developed a so-called "minor damages" system: vehicle owners are entitled to compensation for a reduction in value of 5 to 15 percent of the purchase price without having to return the vehicle.

Case law is constantly evolving. Rogert & Ulbrich monitors current rulings and applies the most favorable legal basis for claims on behalf of its clients.

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Which vehicles and manufacturers are affected?

The thermal window issue is not unique to Volkswagen. Vehicles from almost all manufacturers with diesel engines meeting Euro 5 and Euro 6 emissions standards are affected.

Volkswagen Group: Besides the well-known EA189 manipulation software, thermal windows in vehicles with EA288 engines are also the subject of numerous legal proceedings. VW, Audi, Seat, and Škoda are affected.
Mercedes Benz: This issue has been brought into sharp focus, particularly by the ECJ ruling C-100/21. Several engine types have narrow thermal windows, especially in C-Class, E-Class, and GLC models.
BMW: Legal proceedings concerning thermal windows in various diesel models are underway. BMW denies their illegality.
Opel: Thermal windows in diesel vehicles are the subject of legal proceedings, especially following recalls by the KBA (German Federal Motor Transport Authority).
Fiat Chrysler (Stellantis): Fiat models with 1.6- and 2.0-liter diesel engines are the subject of official investigations in several EU countries.

Whether your vehicle is affected can be checked using the Vehicle Identification Number (VIN) and publicly accessible databases as well as KBA recall lists. Rogert & Ulbrich will check free of charge whether your vehicle is affected.

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We offer you a professional and comprehensive initial consultation in the area of emissions law. Take advantage of this opportunity and avoid mistakes.

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FAQs – Frequently Asked Questions about Thermal Windows

What exactly is a thermal window?

A thermal window is a software function that regulates exhaust gas recirculation (EGR) or other exhaust gas purification systems depending on the outside temperature. At temperatures outside a defined range – typically below 10 to 15 degrees Celsius or above 30 to 35 degrees Celsius – the purification performance is reduced or completely deactivated. The vehicle then only meets the emission limits on the test bench, not in real-world driving conditions.

What specific changes did the 2023 ECJ ruling bring for me as a vehicle owner?

The ECJ ruling C-100/21 clarified that national courts must award damages if an illegal defeat device is present – even without proof of fraud or intent. According to previous German Federal Court of Justice (BGH) case law, this was the biggest hurdle for plaintiffs. Now, proof of the illegal device is sufficient.

Do I have any claims even though I didn't buy the car new?

Yes. The claim for damages is directed against the manufacturer (tort liability), not the dealer. It applies equally to first and subsequent buyers, provided the damage – i.e., the purchase of a defective vehicle at an inflated price – occurred during the specific purchase.

What amount of compensation can I expect?

For minor damages, current Federal Court of Justice (BGH) case law suggests that 5 to 15 percent of the purchase price is a realistic figure. For a purchase price of €40,000, this translates to €2,000 to €6,000 in damages. For major damages, the amount of compensation depends on the purchase price and the mileage driven. Rogert & Ulbrich will assess your specific case individually.

Does the thermal window ruling also apply to manufacturers other than VW?

Yes. The ECJ ruling C-100/21 concerned Mercedes-Benz, but it is considered a precedent for all manufacturers. Courts are applying the principles to BMW, Opel, Fiat, and other manufacturers with comparable thermal windows. The proceedings are ongoing industry-wide.

What is the difference between the diesel scandal and the thermal window?

In the original diesel scandal (starting in 2015), VW used software that actively detected the test bench and only operated in normal mode under those conditions. This was blatant manipulation. The thermal window is more subtle: it reduces exhaust gas purification under certain external conditions that frequently occur in real-world driving situations. Manufacturers long argued that this was technically necessary – an argument that the European Court of Justice largely rejected.

Is my vehicle affected by a software update?

Many manufacturers have offered software updates to adjust the thermal window following regulatory pressure. However, such updates do not automatically invalidate your claims for damages for past events. The damage occurred when you purchased the defective vehicle.

What happens if I have already sold the vehicle?

Even if you have already sold the vehicle in question, you may still have grounds for a claim for damages – provided the statute of limitations has not yet expired. The damage occurred when the vehicle was purchased at a price that did not take the defect into account. Rogert & Ulbrich will examine the statute of limitations situation in your case.

When should I consult a lawyer?

As soon as possible, as statutes of limitations are running. For vehicles whose thermal windows were only legally classified by the 2023 ECJ ruling, the limitation period begins at the end of 2023. The three-year period therefore expires at the end of 2026. Rogert & Ulbrich will check whether your vehicle is affected and initiate the appropriate steps. Many cases are handled through legal expenses insurance.

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Thermal windows in the emissions scandal – compensation and your claims
hire a lawyer now

What a thermal window is, why it is legally relevant, and how vehicle owners can enforce compensation claims.