The California Air Resources Board (CARB) and the US Environmental Protection Agency (EPA) have approved emissions modifications for the last remaining Volkswagen (VW) vehicles containing undisclosed software which deliberately shut down emission control equipment (defeat devices).

The legal process began in 2015 and eventually involved more than a half million diesel VW, Audi and Porsche vehicles in the US. More than 80,000 of those cars are registered in California.

The vehicles affected by the final modification are 3-liter, Generation 1.2 diesels. For these vehicles, the only remaining action is for VW and Audi to submit their resale plans for modified vehicles owners have returned.

VW first publicly admitted the use of illegal defeat devices in September of 2015 after CARB engineers identified the software involved. A defeat device modifies vehicle operations under certain conditions. All defeat devices are illegal.

VW, Audi and Porsche did not disclose the existence of the device and programmed it to operate emission control equipment only when the vehicle was being tested for certification.

The financial settlement in this case is the largest ever agreed to by automakers, totaling more than $20 billion, much of which the company spent to buy back affected cars and on other customer compensation. California has received $423 million for mitigation of harm and VW has agreed to invest $800 million in zero emission vehicle technology in the state over ten years. VW also paid California millions of dollars in civil penalties and compensation.