A major UK court ruling has rejected most of the claims in what has been called “Dieselgate 2.0,” handing a significant victory to Mercedes Benz, Ford, Nissan, Renault and Peugeot Citroën.
The case involved approximately 1.6 million vehicle owners and 20 representative diesel vehicles manufactured between 2012 and 2017. Claimants alleged that the manufacturers used prohibited emissions strategies to make their vehicles perform better during official laboratory testing than they did during normal driving.
According to the Auto Express report on the Dieselgate 2.0 decision, the UK High Court rejected most of the principal allegations. The court found that most of the calibrations examined did not meet the legal definition of a prohibited defeat device.
However, this was not a blanket declaration that every emissions strategy used by every manufacturer was acceptable. The court made adverse findings concerning limited functions used in certain Mercedes Benz and Peugeot Citroën vehicles. The claimants may also seek permission to appeal.
The more interesting question is one that has existed almost as long as laboratory emissions testing:
If a vehicle passes the government’s official test, has the manufacturer complied with the rule, or has it merely learned how to pass the test?
What the UK Court Actually Decided
The case centered partly on the use of “thermal windows.” These are engine control strategies that alter exhaust gas recirculation or other emissions control functions according to temperature and operating conditions.
Manufacturers argue that these strategies may be necessary to prevent condensation, deposits, component failure, sudden power loss or engine damage. Claimants argued that the same strategies reduced emissions controls outside the narrow conditions encountered during an official test.
The High Court concluded that not every calibration or emissions control strategy that changes with operating conditions is automatically a prohibited defeat device. Simply showing that a vehicle produced more nitrogen oxides during other driving conditions was not enough to prove that the manufacturer intentionally designed the system to deceive the regulator.
That distinction matters. An engine control system constantly changes fuel quantity, injection timing, boost pressure, exhaust gas recirculation, catalyst operation and regeneration strategies. A calibration that responds to temperature, load or component protection is not automatically illegal.
At the same time, the court acknowledged that adopting a broader interpretation of “defeat device” could have produced unlawful findings against more of the systems examined.
In other words, much of the result came down to the legal definition being applied, the evidence of intent and whether the manufacturer could justify the strategy as necessary for engine or emissions system protection.
The Original Volkswagen Dieselgate Case Was Different
The original American Volkswagen Dieselgate case was much more direct.
Volkswagen installed software capable of recognizing when certain diesel vehicles were undergoing an official emissions test. During the test, the software enabled the full emissions control strategy. During normal driving, the effectiveness of portions of the emissions system was reduced.
The car was not simply calibrated to perform well over a known test cycle. It actively determined that it was being tested and selected a different operating mode.
The EPA says approximately 590,000 Volkswagen, Audi and Porsche diesel vehicles sold in the United States were equipped with prohibited software defeat devices. Some affected vehicles produced nitrogen oxide emissions as high as 40 times the applicable standard during normal operation.
Volkswagen ultimately agreed to spend as much as $14.7 billion under the initial American settlement covering approximately 500,000 two liter diesel vehicles. The program included buybacks, lease terminations, owner compensation, pollution mitigation and investment in zero emission vehicle infrastructure.
Volkswagen also pleaded guilty to three felony counts and agreed to a $2.8 billion criminal penalty, along with additional civil resolutions.
California separately received substantial settlement money. We covered the state’s final $153 million Volkswagen settlement when it was announced.
Cars Have Always Been Built for the Test
Anyone familiar with manufacturer level emissions certification knows that vehicles are engineered around the applicable test procedure. That is not a secret, and it is not automatically cheating.
Engineers know the speed trace, test duration, vehicle loading, starting temperature, soak requirements, shift schedule and other parameters used during certification. Manufacturers design and calibrate vehicles so they will pass those requirements.
The American Federal Test Procedure, commonly called the FTP, creates a repeatable laboratory standard. Without a repeatable test, it would be difficult to compare one vehicle with another or determine whether a manufacturer complied with a numerical emissions limit.
But a predictable test also gives manufacturers a target.
Gear ratios, shift programming, catalyst light off, ignition timing, fuel control, exhaust gas recirculation and transmission behavior can all be optimized around the areas where the vehicle will operate during the test. Some of this is simply competent engineering. Some of it may satisfy the written procedure while pushing against the purpose of the regulation.
There is an enormous difference between these two situations:
- A manufacturer develops a vehicle that performs especially well over the official test but uses the same disclosed control logic during normal operation.
- A vehicle recognizes that it is being tested and activates a special low emissions mode that is not normally available on the road.
The first may be called engineering to the test. The second can become a prohibited defeat device.
Passing one laboratory run does not necessarily establish that every undisclosed calibration strategy is legal. In the United States, a manufacturer certifies an emissions configuration, including its auxiliary emissions control devices and their operating logic. Software or hardware that bypasses, defeats or renders a required emissions control element inoperative can invalidate that certification.
If Regulators Looked Back Far Enough, What Would They Find?
Volkswagen became the public face of emissions cheating, but it would be naive to assume that clever test specific calibration began or ended with Volkswagen.
If regulators could go back through every calibration, engineering document and certification program used by every manufacturer over the last several decades, they would probably find more than they wanted to see.
At the OEM level, the pressure to meet emissions, fuel economy, performance, durability, drivability and cost targets is immense. Those requirements frequently conflict. More exhaust gas recirculation may reduce nitrogen oxide emissions but increase deposits, particulate production or drivability complaints. A more aggressive emissions strategy may shorten component life. A regeneration strategy may increase fuel consumption. A calibration that protects the engine may increase tailpipe emissions.
Historically, manufacturers sometimes found creative ways to produce the required result during certification. Whether a particular strategy was legal could depend on what was disclosed, how it operated, whether it reduced emissions control effectiveness and whether the manufacturer could justify it as necessary for safe operation or component protection.
That does not mean every manufacturer used an illegal defeat device. It means emissions certification has always involved a continuing contest between the test procedure, the engineers designing around it and the regulators trying to determine whether a vehicle complies outside the most predictable portions of the test.
Volkswagen Was Not the Last U.S. Enforcement Case
In 2024, Cummins agreed to a record $1.675 billion civil penalty over alleged Clean Air Act violations involving diesel engines installed in RAM 2500 and RAM 3500 trucks. The complete settlement was valued at more than $2 billion when recall, repair and mitigation obligations were included.
Federal and California regulators alleged that more than 630,000 model year 2013 through 2019 trucks contained illegal emissions control software defeat device features. Those strategies allegedly helped the trucks pass standard EPA tests while reducing the effectiveness of emissions controls during normal driving.
We previously covered the related Cummins settlement with the California Air Resources Board.
Following Volkswagen, the EPA expanded the use of nonstandard test cycles and normal but less predictable operating conditions. That is an important enforcement tool. If a vehicle only remains clean while following the exact certification trace, changing the trace can expose the strategy.
California has also warned manufacturers that they must disclose software and hardware changes that affect emissions. Our earlier article covers the CARB warning concerning undisclosed emissions related software and hardware.
Passing the Test Versus Meeting the Standard
There is a legitimate argument that a manufacturer should not be punished merely because engineers understood the test and designed a vehicle to pass it. Government writes the procedure. The manufacturer follows the procedure. The vehicle passes. From that perspective, the manufacturer did what the regulation required.
But that argument has limits.
If the certification represents that the vehicle uses a particular emissions control configuration, while undisclosed software substantially reduces that control during normal operation, the vehicle has not merely been optimized for the test. The test has been used to conceal how the certified product actually operates.
The line between the two can be technically and legally complicated. It may depend on intent, disclosure, component protection, ambient temperature, normal use and the exact language of the regulation.
That is why the UK Dieselgate 2.0 ruling should not be reduced to “the manufacturers were innocent” or “every diesel manufacturer cheated.” The court examined specific systems under a particular legal standard and concluded that most of the challenged strategies had not been proven to be prohibited defeat devices.
That is considerably narrower than saying the vehicles were equally clean during every form of real world driving.
Why This Matters for Imported Vehicles
Emissions certification and registration are separate from simply passing a local tailpipe inspection. A vehicle can produce acceptable numbers during one test and still lack the documentation or certified configuration required by federal or California law.
Anyone importing a vehicle should understand the difference between federal EPA eligibility, California emissions certification and periodic state inspection requirements.
Useful related information includes:
- EPA requirements for importing vehicles and engines
- EPA Independent Commercial Importers
- The federal 21 year EPA exemption for vehicles in original configuration
- California requirements for direct import vehicles from 1975 or newer
- California requirements for direct import diesel vehicles
- California certification procedures for used direct import vehicles
The Bottom Line
Manufacturers build vehicles to pass government tests because that is how certification works. A repeatable test is necessary, and designing a compliant vehicle around that procedure is not automatically improper.
The problem begins when a vehicle does not merely perform well during the test, but recognizes the test and temporarily becomes a different vehicle.
Volkswagen crossed that line in the United States. The UK High Court concluded that most of the strategies examined in the Dieselgate 2.0 litigation had not been proven to cross it under British law. Limited exceptions remained, and appeals may follow.
The broader lesson is that laboratory compliance and real world emissions have never been exactly the same thing. Regulators write a test, manufacturers learn how to pass it, and regulators eventually expand the test after discovering how it was being used.
That cycle will continue as long as certification depends on a predictable laboratory procedure and the consequences of failing it are measured in billions of dollars.
Sources: UK High Court Pan NOx liability judgment, Auto Express, U.S. EPA Volkswagen violations, and U.S. Department of Justice Cummins settlement.
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