Volkswagen's emissions-rigging scandal has widened after the company said it had understated carbon dioxide emissions for 800,000 of its cars.

The admission adds to the scandal in which the carmaker said 11 million of its vehicles globally had software that allowed them to cheat on emissions tests for a different pollutant, nitrogen oxide.

Here are key dates since the scandal broke:

Sept. 18: The U.S. Environmental Protection Agency says Volkswagen installed software on 482,000 cars that enabled them to cheat on emissions tests. The software reduced nitrogen oxide emissions when the cars were placed on a test stand but then allowed higher emissions and improved engine performance during normal driving.

Sept. 22: Volkswagen says about 11 million diesel vehicles worldwide were fitted with the deceptive software. It sets aside 6.5 billion euros ($7.3 billion) to deal with the costs of the scandal, including expected recalls.

Sept. 23: Volkswagen CEO Martin Winterkorn resigns. He takes responsibility for the "irregularities" found by U.S. inspectors, but insists he personally did nothing wrong.

Sept. 25: Volkswagen appoints Matthias Mueller, the head of the group's Porsche unit, as the new CEO.

Sept. 28: German prosecutors open an investigation to establish what role former CEO Winterkorn had in the scandal. Winterkorn is not charged or suspected of wrongdoing, but is named in the investigation because under German law it is not possible to bring charges against a company, only individuals.

Sept. 29: Volkswagen says it has commissioned an external investigation by U.S. law firm Jones Day.

Oct. 1: Volkswagen names Hans Dieter Poetsch, its chief financial officer, as the new board chairman. The move had been planned since before the crisis but raises concerns about the ability of longtime insiders to get to the bottom of the matter.

Separately, Volkswagen says it has dropped a shift a week at one engine factory and imposed a temporary hiring freeze at its financial services division.

Oct. 2: Volkswagen starts offering customers online checks to see if their cars are affected.

Oct. 6: CEO Mueller announces review of all investment spending.

Oct. 7: CEO Mueller says the recall of cars with the emissions-rigging software should start in January and that Volkswagen aims to fix them all by the end of next year.

Oct. 8: Volkswagen's top U.S. executive, Michael Horn, testifies to Congress, apologizing for the scandal.

Oct. 15: Germany orders recall of all Volkswagen cars with the test-cheating software. By European Union rules, Germany's move means that all 8 million such cars are obliged to be recalled across the 28-country bloc.

Oct. 28: Volkswagen reports a loss of 1.67 billion euros ($1.83 billion) in the third quarter after booking a charge of 6.7 billion euros to cover the costs of recalls connected to the scandal.

Nov. 2: The Environmental Protection Agency and the California Air Resources Board say Volkswagen also installed the cheating software on thousands of Audi, Porsche and VW cars with six-cylinder diesel engines. The previous revelations of cheating involved four-cylinder diesels in smaller cars. Volkswagen rejects the new allegation.

Nov. 3: Volkswagen says it had understated carbon dioxide emissions for 800,000 cars. The development could cost the company another 2 billion euros ($2.2 billion).