It's been a year since the U.S. Environmental Protection Agency (EPA) revealed that Volkswagen used illegal "defeat device" software that allowed its diesel cars to cheat emissions tests.
The VW diesel scandal may be just the beginning, though.
Because while Volkswagen continues to negotiate with regulators and customers in the U.S., it seems that other carmakers in Europe engaged in similar measures to game the system.
European fuel economy and emissions tests have a reputation for being lax, and a new study claims European automakers have taken full advantage of that.
In fact, Volkswagen may actually be selling the least polluting diesels in Europe, according to advocacy group Transport & Environment (T&E).
The group's full study (pdf) of 230 diesel-car models measured how well automakers complied with both Euro 5 emissions standards that were in effect between 2011 and 2015, and current, stricter Euro 6 standards.
It found that not one model from any carmaker met Euro 6 standards in real-world driving.
VW was found to have the cleanest Euro 6 cars, although it also had the dirtiest Euro 5 cars.
T&E attributes this to technology changes implemented in anticipation of the Euro 6 standards, the first phase of which took effect in January 2015.
The final Euro 6 standards only bring European Union nations to where the U.S. has been since 2008, and even that level won't be reached until the next phase of the standards is implemented January 1.
Automakers selling cars in Europe aren't even meeting the current standards, according to the study.
Fiat and Suzuki were the worst offenders in terms of the Euro 6 standards, with diesel cars averaging 15 times the legal limit of nitrogen-oxide (NOx) emissions in real-world use.
In addition, Renault-Nissan vehicles averaged 14 times the legal levels of NOx, while models from General Motors' Opel and Vauxhall divisions averaged 10 times the legally-allowed amounts of NOx.
In comparison, Volkswagen models averaged only twice the amounts of pollutants allowed by the Euro 6 standards.
T&E also estimated that there are currently 29 million diesel cars on European roads that emit at least three times the legal levels of NOx under the less-strict Euro 5 standards.
All of the models studied were approved for sale by European regulators, despite apparently being unable to meet the relevant emissions standards.
This underscores the need for real-world emissions testing that can provide more accurate results than the current laboratory testing.
It also indicates that manufacturers simply may not be able to get their diesels to meet emissions standards at prices that buyers will be willing to pay.
Renault recently admitted that it may have to stop selling diesels in Europe, because the cost of complying with anticipated stricter standards may be too great.