Questions and answers about Volkswagen's emissions testing crisis

German automaker Volkswagen AG admits that it rigged U.S. emissions tests so it would appear that its diesel-powered cars were emitting fewer nitrogen oxides, which can contribute to ozone buildup and respiratory illness. Here are some questions and answers about the ongoing crisis:

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WHICH VEHICLES DOES THIS AFFECT?

Volkswagen installed software in roughly 482,000 diesel passenger cars sold in the U.S. since 2008, according to the U.S. Environmental Protection Agency. The software turned on the cars' full emissions control systems when the cars were being tested by the government, and then turned off those systems during normal driving. The Jetta, Beetle, Audi A3 and Golf from the 2009-2015 model years are affected, as well as the Passat from the 2014-2015 model years. Volkswagen has halted the sale of 2015 models and is prohibited from selling 2016 models until they are fixed.

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WHAT SHOULD CUSTOMERS DO?

Volkswagen will fix the cars for free as soon as it develops a remedy. Owners will be notified when there's a fix. In the meantime, the cars are safe to drive. Car-buying site Edmunds.com cautions owners against selling the cars right now if they don't have to, since they can expect a lower trade-in value.

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WHAT DOES VOLKSWAGEN SAY?

The EPA Volkswagen Group CEO Martin Winterkorn issued a statement Sunday saying that the company will fully cooperate with government investigations and has ordered its own probe. Winterkorn said, "I personally am deeply sorry that we have broken the trust of our customers and the public."

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WHY WOULD VOLKSWAGEN DO THIS?

Experts think Volkswagen may have wanted to avoid the cost of additional hardware to meet tough U.S. emissions standards, so it came up with a cheaper software fix. The software also would have helped the cars' fuel economy numbers, since they get better gas mileage when the emissions control system is turned off.

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DOES THIS AFFECT OTHER DIESEL VEHICLES IN THE U.S.?

Not so far. Thirteen brands currently offer diesels in the U.S., including Ram, Chevrolet, Mercedes-Benz and BMW. West Virginia University, which conducted the tests that led to the discovery of Volkswagen's software, said the BMW it tested passed. On Monday, the Environmental Protection Agency said that it will screen other automakers for the so-called "defeat devices" that VW used to thwart emissions standards in its diesels.

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WHAT'S NEXT?

The U.S. government could fine Volkswagen $37,500 per vehicle for the violations, a total of more than $18 billion. It could also levy fines against individuals of $3,750 for each violation, or potentially $1.8 billion. The U.S. Justice Department, the California Air Resources Board and German authorities are also investigating.

House Energy and Commerce Committee Chairman Fred Upton, R-Mich., said Monday that the panel's subcommittee on oversight and investigations will hold a hearing "in the coming weeks" on VW's use of the defeat devices.

Winterkorn will face scrutiny from Volkswagen's board, which meets Friday, and investors, who punished the company by sending its shares down 17.1 percent Monday to a three-year low.

At least one class action lawsuit has been filed on behalf of owners in the U.S.; others will likely follow.