Volkswagen's cheating engines can't be easily fixed

Volkswagen is confronted with a monumental challenge.

The company has admitted that 11 million of its cars used illegal software to cheat emissions standards.

Now, many owners are demanding that the offending cars be fixed.

That's easier said than done, and Volkswagen has already tried — and failed — twice.

Here's the issue, according to the US Environmental Protection Agency: Cars with Volkswagen's2-liter TDI turbo-diesel four-cylinder engines include software that detects when the car is undergoing emissions testing and turns on a suite of pollution-control systems.

More