VW's confession that it illegally programed the software in 11 million diesel-powered cars to cheat on emissions tests comes with the sting of betrayal for owners. The automaker's been touting the benefits of "clean diesel" for years, and it dominates the American market for the gasoline alternative.

Last week, the EPA accused the German automaker of using a "defeat device," an algorithm that detects when the car is being tested by the EPA and changes its performance to meet emissions standards. The rest of the time, the cars produce up to 40 times the legal limit of nitrogen oxides (NOx), the stuff linked to increased rates of asthma and other respiratory problems.

The accusation applies to 482,000 diesel-powered, four-cylinder Jetta, Beetle, Audi A3, and Golf cars sold between 2008 and 2015 in the US, and to Passat cars sold from 2014 to 2015. Today, Volkswagen said the software is present on 11 million cars worldwide. "I personally am deeply sorry that we have broken the trust of our customers and the public," CEO Dr. Martin Winterkorn said in a statement. The company has denied rumors he will resign.

The Jettas, Beetles, Passats, and Audis in question deliver top tier fuel economy, and, eco-conscious owners were told, had no trouble meeting strict emissions standards. The 2015 A3 delivers 36 mpg, the 2015 Golf Sportwagen does 35. In 2008, the 2009 Jetta TDI was named Green Car of the Year by the Green Car Journal. This year, Cars.com named the 2015 Passat TDI its “Eco-friendly Car of the Year.” These cars were green for the budget, green for the environment.

Once the sting of the lie fades, the US customers who bought 482,000 of those cars will feel the real pain. Because Volkswagen will be forced to recall those vehicles and somehow make them to meet federal standards. There are two apparent ways to do that, and owners who value performance, fuel economy, and trunk space won't like either.

Just Run It In Test Mode

One is to "reflash" the engine control module, recalibrating the software so the car always runs the way it does during EPA testing, and always meets emission standards.

The downside here is that to achieve the drastic drop in NOx emissions, the cars in test mode sacrificed some fuel economy, or performance. Just how much is hard to say, but any drop in torque—one great thing about diesels is how they accelerate off the line—will not make drivers happy. And a drop in mileage would likely cost VW, since hundreds of thousands of drivers would have to spend more on fuel than VW promised at the time of sale.

There's precedent for this: Last year, the EPA forced Kia and Hyundai to downgrade fuel economy ratings on more than a million cars (they blamed “procedural errors” at a shared testing facility). The Korean automakers spent $395 million on a settlement with vehicle owners aggrieved over higher than expected fuel costs.

Slap on the Urea Tank

The standard way of making a diesel run cleanly is to use selective catalytic reduction, a chemical process that breaks NOx down into nitrogen and water. Part of that process includes adding urea to the mix. The super effective system can eliminate 70 to 90 percent of NOx emissions, and is used by other diesel manufacturers like Mercedes and BMW. The downside is that it adds complication to the system, and cost—$5,000 to $8,000 per car. And you need to periodically add the urea-based solution to your car to keep it working.

The big "advance" from VW was the "clean diesel" technology that supposedly made the whole urea thing unnecessary on its smaller cars, like the Beetle, Jetta, and Audi A3—the very models being recalled because they don't meet emissions standards under real-world driving conditions.

So it seems the logical way to get those cars to perform like their diesel cousins is to add a urea. VW's unlikely to embrace that option, because adding hardware to half a million cars would be far more expensive than a computer update. It wouldn't be any fun for the TDI owner, either. Not only do you have to spend an afternoon with your local dealer, you have to make room for the tank. That could mean sacrificing cargo space or giving up the spare tire.

Dodge the Recall

So if the government is making VW recall your car and your fuel economy and performance will take a hit because of it, why not just ignore the recall notice in your mailbox? People ignore recalls all the time, even when they're to fix critical safety issues. A 2011 GAO report found just 65 percent of recalled cars are repaired. The man can't compel you to get it fixed.

Except here, maybe he can. These Volkswagens are a public health threat and exuberantly break federal law. It's not crazy to think state agencies or NHTSA would flag them, and refuse to issue a new registration, or let them pass a smog test, unless proof of a fix is offered. "It should be fairly easy to police," says Matt DeLorenzo, managing editor of news at Kelley Blue Book.

Whether you dodge the recall or not, your car's resale value is likely to drop as far and fast as VW's stock, which has plunged 20 percent since the feds came down on VW Friday.