Judgment handed down in Diesel Emissions litigation: Court rejects large majority of allegations against car manufacturers

10/07/26

Cockerill LJ has handed down her judgment on key liability issues in the diesel emissions litigation, following a lengthy trial that began in October 2025 and concluded in March 2026 (the “PDD Trial”). This is the largest group litigation in the history of this jurisdiction, with c.1.6 million claimants across numerous Group Litigation Orders being case-managed together. Members of Brick Court appeared for Mercedes, the first of five Lead Defendants (the others being Ford, Renault, Nissan and Peugeot-Citroen). Other members of Brick Court appeared for the non-Lead Defendants participating in the trial in relation to legal issues.

The focus of the PDD Trial was on determining the correct legal approach to determining whether a vehicle contains a prohibited defeat device (“PDD”) under Articles 3(10) and 5(2) of EU Regulation 715/2007 (the “Emissions Regulation”); and, applying the correct legal approach, determining whether certain sample vehicles contained PDDs.

On the core legal issue, i.e. the meaning of ‘defeat device’ in the Emissions Regulation, the Court accepted the arguments of Mercedes and other Lead Defendants, and held that a defeat device is (and is only) a device which senses one or more parameters of the regulatory emissions test (including its boundary) and objectively operates with the purpose of causing the ECS to work more effectively when it senses that it is being subjected to a test cycle compared to how it works in out of test driving (referred to in the judgment as a Cycle Recognition Defeat Device or “CRDD”). A CRDD will be a PDD unless justified under Article 5(2) of the Emissions Regulation, which the judgment also interprets. The Court also made findings as to the meaning of the phrase “conditions which may reasonably be expected in normal vehicle operation and use” in Article 3 (10), rejecting the Claimants’ case in relation to those matters.

Applying that approach, the Court rejected the large majority of the Claimants’ PDD allegations against Mercedes and the other car manufacturers. The Claimants had alleged that each of the four Mercedes sample vehicles contained many PDDs, which the judgment groups together under ten headings. Nine of those allegations failed completely and three of the four Mercedes sample vehicles have been held not to contain (and never to have contained) any PDD. The Judge held that one functionality, which was used in one of the Mercedes sample vehicles in its initial calibration and (as was common ground) was removed by software updates made freely available by Mercedes, was a PDD.

The Judge also considered what the position would have been if she had adopted the Claimants’ preferred approach to the meaning of a ‘defeat device’. On this approach too, the Judge held that the large majority of the Claimants’ allegations would have failed, with nine of the ten groups of PDD allegations against Mercedes failing altogether, and one allegation succeeding in respect of a functionality appearing in two of the Mercedes sample vehicles as originally calibrated and which (as was again common ground) had been removed by software updates made freely available by Mercedes.

The Court also determined certain legal issues concerning actionability. Cockerill LJ held that, on the basis of her interpretation of Articles 3(10) and 5(2) of the Emissions Regulation, breach of those provisions was actionable in principle as a breach of statutory duty, but rejected the Claimants’ argument that the presence of a PDD in a vehicle would ‘axiomatically’ and without more amount to a breach of the statutorily implied warranties of satisfactory quality and compliance with description.

The judgment can be found here [link]. All consequentials have been deferred to a later date.