Volkswagen is taking another $3 billion charge to fix diesel engines in the US, lifting the total bill for its emissions test cheating scandal to around $30 billion. 

Shares in the German carmaker fell as much as 3% today, as traders and analysts expressed dismay the company was still booking charges two years after the scandal broke. 

Europe's biggest car maker admitted in September 2015 it had used illegal software to cheat US diesel emissions tests, sparking the biggest business crisis in its 80 year history. 

Before today, it had set aside €22.6 billion to cover costs such as fines and vehicle refits. 

It said today that hardware fixes were proving tougher than expected, as it booked an additional €2.5 billion provision. 

"We have to do more with the hardware," a Volkswagen spokesman said, adding US customers were having to wait longer for their cars to be repaired. 

The news relates to the programme to buy back or fix up to 475,000 2 litre diesel cars. 

In Europe, where only a software update is required for the 8.5 million affected cars, besides a minor component integration for about 3 million of those, fixes are running smoothly, the spokesman added. 

The additional provision will be reflected in third-quarter results due on October 27, VW said. 

Asked why VW did not see the problem sooner, the spokesman said it had made provisions based on what it expected at the time. "It has now become clear that we need to do more," he said. 

Volkswagen said in September 2015 that around 11 million vehicles worldwide could be fitted with software capable of cheating emissions tests. 

Porsche, which owns a 30.8% stake in VW, said the new provision would also affect its results, but stuck to the wide range for its expected 2017 post-tax profit of €2.1-3.1 billion.

Meanwhile, Munich prosecutors have arrested a former board member of Porsche in connection with the emissions scandal at VW's premium brand Audi, a person familiar with the matter has said. 

Audi admitted in November 2015, two months after parent VW's emissions scandal broke, that its 3 litre V6 diesel engines were fitted with an auxiliary control device deemed illegal in the US.