Formal Legal Action Filed
Hagens Berman EMEA LLP has officially brought a formal legal action on behalf of consumers at the UK High Court against Mercedes accusing it of using illegal emissions-cheating devices. It is alleged Mercedes’ fraud between 2008 and 2018 affected more than 300,000 vehicles owned by individuals and businesses in England and Wales during this period of time.
ABOUT THE CLAIM
A US class action led by Hagens Berman EMEA LLP’s parent firm, Hagens Berman Sobol Shapiro LLP, revealed that when tested at motorway speeds, at low temperatures, and at variable speeds, certain model year Mercedes diesel vehicles systemically failed to meet US emissions standards. For example, low temperature testing at motorway speeds produced emissions 8.1 to 19.7 times the legal standard. Hagens Berman settled that matter in favour of clients and had reason to believe Mercedes engaged in similar behaviour in England and Wales. With our expertise gained in the US case, Hagens Berman EMEA LLP investigated the systemic failure of Mercedes vehicles under UK and EU laws dictating emissions levels and filed a claim at the UK High Court.
HOW DOES THE MERCEDES AFFECTED EMISSIONS SYSTEM WORK?
Daimler allegedly used multiple techniques to reduce emission levels in testing conditions. These devices and software are referred to as ‘cheating devices’ and allegedly include:
- Initial reduction of oxides of nitrogen (NOx) performed by the exhaust gas recirculation (EGR) system.
- A diesel oxidation catalyst that reduces the amounts of carbon monoxide (CO) and hydrocarbons (HC) released from the exhaust and helps keep the particulate trap clean.
- A particulate filter that traps and stores soot particles. The diesel oxidation catalyst upstream helps to remove the particles from the particulate trap, though the engine will occasionally remove excessive particulate buildup by raising the exhaust temperature.
- In some older model vehicles, a NOx storage catalyst performs the final removal of NOx from the exhaust before it exits the tailpipe.
- The vast majority of defeat device-equipped Mercedes vehicles also make use of a Selective Catalytic Reduction (SCR) catalytic converter (instead of a NOx storage catalyst) to convert remaining nitrogen oxides to nitrogen and water. A solution of urea and water, “Diesel exhaust fluid” (DEF), is injected into the exhaust gas stream to enable conversion.
To prevent vehicles from breaking emissions regulations, the engine may go into a limp-home-mode if the DEF tank is depleted. Drivers are instructed to keep the tank refilled as necessary. Some commercial vehicles are equipped with a request or inhibit switch, which "postpones" DEF injection, as it can reduce power output and temporarily increase temperature. If the vehicle is climbing a grade, for example, it may be necessary to delay the cycle.
ENVIRONMENTAL EFFECTS OF EMISSIONS
In the U.S. Hagens Berman Sobol Shapiro LLP successfully alleged diesel engines pose a particularly difficult challenge to the environment because they have trade-off between power, fuel efficiency and emissions: the greater the power and fuel efficiency, the dirtier and more harmful the emissions.
Compared to petrol engines, diesel engines generally produce greater torque, greater low-end power, better drivability and much higher fuel efficiency. But these benefits come at the cost of much dirtier and more harmful emissions, including NOx, which include a variety of nitrogen and oxygen chemical compounds that only form at high temperatures.
CURRENT STATUS OF THE LITIGATION
Following a 10-week liability (fault) trial, which started Monday 13 October 2025, Hagens Berman EMEA LLP sought to determine whether certain diesel cars manufactured by Mercedes and its behavior and conduct when using an alleged "defeat device" software in its diesel cars to cheat emissions tests was illegal, making them seem clean in labs while polluting the environment greater than the legal limit for NOx in real-world driving conditions.
With that trial concluding on 18 December 2025, a judgment on liability is expected in the summer of 2026.
While awaiting the court to rule on liability trial, legal representatives in the claim on all sides continue to prepare proactively for a quantum trial scheduled in October 2026, during which the separate issue of damages will be discussed. A quantum trial is not a separate type of case but follows once liability is decided, where the court will determine the quantum (amount) of money to be paid as compensation to claimants.