The ongoing controversy around Volkswagen's emission scandal has shocked the officials at the United States Environmental Protective Agency (U.S. EPA) with its CEO, Martin Winterkorn announcing his retirement on Wednesday, September 23. The German automaker is facing accusations of cheating because of its misleading advertisements around diesel cars promising better mileage and cleaner emissions. The Volkswagen power plant is seen from the railway station in Wolfsburg, Germany Here is all you need to know about the Volkswagen emissions scandal:

3. On September 18, U.S. and California environmental regulators accused Volkswagen AG of deliberately circumventing clean air rules on nearly 500,000 diesel cars which could face $18 billion penalties.

4. On September 20, Volkswagen CEO, Martin Winterkorn publicly apologised for the violations.

The organisation's shares plunged by nearly 20 percent on September 21, after the German carmaker admitted it had rigged emissions tests of diesel-powered vehicles in the United States.

A file photo of Volkswagen CEO Martin Winterkorn at an event

5. After consistent pressure from various quarters, CEO Martin Winterkorn resigned from his post on September 23.

Different countries across the world have launched their respective probes against Volkswagen automobiles. Volkswagen Group of America CEO Michael Horn admitted, "We've totally screwed up. Our company was dishonest with the EPA, and the California Air Resources Board and with all of you." The organisation admitted that about 11 million cars have been hit by the scandal.

Newly shipped Volkswagen vehicles sit on a back lot at a Volkswagen dealership in San Diego, California