The new Audi A4 models are presented at an auto show in Frankfurt this month. Audi says 2.1 million of its diesel cars worldwide are fitted with sophisticated software enabling them to cheat emission tests. (Odd Andersen/AFP/Getty Images, files)

Luxury-car brand Audi said Monday that 2.1 million of its cars around the world were outfitted with software that enabled them to cheat emissions standards.

The announcement clarifies Audi’s role in the diesel-emissions scandal roiling its parent company, Volkswagen. The German automaker admitted last week to installing the software in about 11 million cars around the world, which includes the 2.1 million Audis, spokesman Jürgen De Graeve said.

The affected Audi models include the A1, A3, A4, A5, A6, TT, Q3 and Q5, but the scope was more limited in the United States, where diesel cars are less popular.

About 13,000 of the cars were in the United States, where only the A3 model was affected, Audi USA spokesman Brad Stertz said.

This isn’t the first time Audi has faced a massive scandal because of trouble with its cars. In 1987, the automaker was forced to recall more than 250,000 cars because they accelerated unexpectedly.

Audi’s sales in the United States tanked after the revelation, and it took more than a decade for them to rebound, highlighting the challenge Volkswagen and its luxury brand could face as it tries to win back customers’ trust amid a scandal centering on deception, Deutsche Bank analysts said in a research note last week.

“Back in the days, Audi suffered a massive loss in reputation and this wasn’t even about cheating,” the analysts wrote.

Volkswagen shares plunged 7.5 percent Monday. About two-fifths of its stock market value has been wiped out since the scandal erupted.

The potential cost to the world’s largest automaker is still unknown, but it is expected to be staggering.

Volkswagen could be subject to up to $18 billion in fines from the Environmental Protection Agency alone and is under investigation by the Justice Department.

Government officials in Germany and other parts of Europe have launched separate probes, including one into former chief executive Martin Winterkorn, who resigned last week.

Reuters reported Monday that the company has suspended staff from some of its divisions, including Audi, Porsche and Volkswagen.

A spokesman for Volkswagen in Germany couldn’t immediately be reached for comment Monday, but the executive committee of the company’s board said in a statement Friday that it had recommended the “immediate suspension of some employees.”

Moore is a freelancer.