UK High Court Largely Rejects Diesel Emissions Claims Against Automakers in Landmark Case

The case is described as the largest group claim trial in English and Welsh history, representing around 1.6 million vehicle owners.
Citroën faced an unfavorable ruling regarding its 'split mode' combustion in at least one vehicle, identified as a defeat device.
The court dismissed most of the principal allegations that the tested vehicles used prohibited defeat devices to cheat emissions tests.
Mercedes-Benz welcomed the ruling and said it was 'very largely in favour' of the brand.
The ruling sets the tone for subsequent proceedings and paves the way for tens of thousands of additional claims against the automakers.
A UK High Court judge has ruled largely in favor of major automakers in one of the biggest emissions fraud cases in British legal history, dismissing most allegations that car manufacturers used illegal devices to cheat diesel emissions tests. The case, covering around 1.6 million vehicle owners, represents the largest group claim trial ever seen in England and Wales, according to Ford Authority.
Judge Sara Cockerill examined 20 sample vehicles from brands including Mercedes-Benz, Ford, Nissan, Renault, and Stellantis labels Peugeot and Citroën. The court rejected the bulk of the central claims. Mercedes-Benz said the ruling was 'very largely in favour' of the brand, according to Market Screener.
The ruling centered on so-called defeat devices — software or hardware that detects when a car is being tested and reduces emissions only during the test. The court found that most of the vehicles in the sample did not use such prohibited devices, according to Morningstar. That outcome was a major win for the automakers.
Citroën was the notable exception. The court found an unfavorable result against the French brand over its 'split mode' combustion system in at least one vehicle, identifying it as a defeat device. That finding keeps pressure on Citroën even as its parent Stellantis largely escaped the worst outcomes, according to Market Screener.
Mercedes-Benz was quick to welcome the decision. The German automaker called the ruling 'very largely in favour' of the brand. Ford, Nissan, and Renault also saw most claims against them thrown out. For these companies, the ruling removes a significant cloud of legal risk that had hung over them for years, according to Market Screener.
The automakers had faced accusations similar to those in the 2015 Volkswagen scandal — often called 'dieselgate' — where VW admitted to rigging emissions tests worldwide. That case cost Volkswagen over $30 billion in fines and settlements globally. This UK ruling suggests the same scale of fallout may not hit the other brands involved here.
This ruling is only the first stage. Around 1.6 million vehicle owners still have active claims in the broader litigation. The 20 sample vehicles tested in this phase were used to set legal precedents that will shape tens of thousands of future cases, according to Ford Authority. Those proceedings now move forward with clearer legal ground.
Lawyers for claimants are reviewing the judgment. The Citroën finding shows at least some vehicle owners may still have a path to compensation. But for most claimants, the road ahead looks harder after the court threw out the main allegations, according to Morningstar.
The UK case swept in a wide range of major brands. Alongside Mercedes, Ford, Nissan, Renault, Peugeot, and Citroën, the litigation also named Volvo, Jaguar Land Rover, and Vauxhall, according to Ford Authority. The case has moved through the courts slowly, reflecting the enormous complexity of testing vehicle software and emissions systems across dozens of models.
With this first stage now decided, the court has a clearer framework for what counts as a defeat device under UK law. That definition will be critical for every remaining claim. For the automakers still facing further rounds of litigation, the ruling is a relief — but not a full exit from the courtroom.
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