Shares in VW have fallen 10% this morning after it reported "irregularities" in carbon dioxide emissions levels, which could affect around 800,000 cars in Europe.
The firm said the problem could cost about €2bn (£1.4bn).
Brands including VW, Audi, Skoda and Seat could be affected. Whilst the issue mainly affects diesels, it could also include petrol models.
As yet Volkswagen has not said whether or not it believes those irregularities were caused by deliberate action, and it also has not specified which models are affected.
Whilst VW is currently feeling the heat, I would wager good money that other car manufacturers also fiddled their data emissions.