Volkswagen: The scandal explainedBy Russell Hotten Business reporter, BBC News 7 October 2015From the section BusinessImage copyright Getty Images What is Volkswagen accused of?It's been dubbed the "diesel dupe". The Environmental Protection Agency (EPA) found that manyVW cars being sold in America had devices in diesel engines that could detect when they were being tested, changing the performance accordingly to improve results. The German car giant hassince admitted cheating emissions tests in the US.VW has had a major push to sell diesel cars in the US, backed by a huge marketing campaign trumpeting its cars' low emissions. The EPA's findings cover 482,000 cars in the US only, including the VW-manufactured Audi A3, and the VW brands Jetta, Beetle, Golf and Passat. But VW has admitted that about 11 million cars worldwide, including eight million in Europe, are fitted with the so-called "defeat device".The device sounds like a sophisticated piece of kit.Full details of how it worked are sketchy, although the EPA has said that the engines had computer software that could sense test scenarios by monitoring speed, engine operation, air pressure and even the position of the steering wheel. When the cars were operating under controlled laboratory conditions - which typically involve putting them on a stationary test rig - the device appears to have put the vehicle into a sort of safety mode in which the engine ran below normal power and performance. Once on the road, the engines switched out of this test mode. The result? The engines emitted nitrogen oxide pollutants up to 40 times above what is allowed in the US.