For years, Volkswagen promoted its TDI models under the "clean diesel" banner, portraying them as environmentally superior, due to their high fuel economy while (supposedly) meeting strict new emissions standards.

We now know the company was actually using "defeat device" software to mask its diesels' inability to meet those standards in real-world use.

The "clean diesel" tagline is now a punchline, and it has become the basis for a new lawsuit against VW.

DON'T MISS: VW diesel scandal now 6 months old; what have we learned?

The Federal Trade Commission (FTC) is now suing the embattled German carmaker, claiming it deceived customers with its "clean diesel" advertising.

The FTC is seeking a court order requiring Volkswagen to compensate U.S. owners of affected TDI vehicles, as well as an injunction "to prevent Volkswagen from engaging in this type of conduct again," according to an agency press release.

It said the lawsuit will seek compensation for owners who bought or leased their cars between late 2008 and late 2015.

Volkswagen TDI

Volkswagen TDI

“Volkswagen has received the complaint and continues to cooperate with all relevant U.S. regulators, including the Federal Trade Commission," a company statement said.

"Our most important priority is to find a solution to the diesel emissions matter and earn back the trust of our customers and dealers as we build a better company," it concluded.

The FTC complaint alleges that VW's "clean diesel" advertising campaign—which included print advertising, social-media campaigns, and even Super Bowl ads—often targeted "environmentally-conscious" consumers.

ALSO SEE: VW diesel emissions scandal: what you need to know in 10 questions (updated)

Many of the claims in those ads were specifically related to low emissions and thus patently false, the FTC notes.

These included claims that TDI models met "stringent emissions requirements," were "50-state compliant," and promises that the cars would have high resale values.

Independent researchers eventually discovered that these vehicles could not meet Federal emissions standards without cheating, and now owners are stuck with cars that are rapidly losing value.

2009 Volkswagen Jetta TDI

2009 Volkswagen Jetta TDI

Some ads also specifically touted low emissions of nitrogen oxides, but some models were later found to emit 40 times the legal limit.

Volkswagen's promotion of diesels as "clean" has been a particular source of anger for customers, many of whom bought cars for the supposed environmental benefits.

MORE: Deadline for regulators, VW to agree on diesel changes extended to April 21

The company "ripped off mindful consumers who thought they were purchasing cleaner vehicles," Kathryn Phillips, Sierra Club California director, adding that the FTC "is right for filing this lawsuit."

"There's really no end in sight to this situation," said Rebecca Lindland, senior analyst for Kelley Blue Book.

2009 Volkswagen Jetta TDI

2009 Volkswagen Jetta TDI

Every government agency that is "even remotely impacted" by the diesel scandal will likely file a lawsuit, or seek some other form of compensation for perceived damages, she predicted.

While Volkswagen contends with a growing number of lawsuits, the company appears no closer to agreeing with the EPA and the California Air Resources Board on an actual fix for the nearly 600,000 affected diesel cars in the U.S.

Those three parties missed a March 24 deadline and were granted a postponement by a U.S. District Court judge who set the requirement; they now have until April 21 to come up with a satisfactory plan.


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