4 November 2015 Last updated at 11:36 GMT
There was a drop in shares in VW after it reported "irregularities" in carbon dioxide emissions levels, which could affect around 800,000 cars in Europe.
Arndt Ellinghorst, who used to work for VW and is now head of automotive research at investment firm Evercore, speaks to the Today programme.
The emissions-testing scandal at Volkswagen has now widened.