As far as hot seats in the car industry go, the one occupied by Mr Herbert Diess, chairman of the board of management of the Volkswagen passenger-car brand, became molten when the company's global diesel emissions scandal broke in September.

How could a German industrial giant that prides itself on engineering integrity cheat in emissions tests? That is a question the world is asking, but it is also one that stumps Mr Diess and his fellow board members.

"It's very hard to understand how it could happen over such a long period of time," says the 57-year- old, who became chairman just two months before the scandal broke. "Believe me, we question everything now and we will fully disclose what we find out and then we will make sure that it cannot happen again.

"We have to find out how it happened, what really happened, who was involved."

But at this point, he believes "it was a relatively small team in engineering that did it".

He says the 11 million vehicles affected by the scandal - which involves a device that is able to lower nitrogen oxide emissions when the vehicle is being tested but is inactive when the car is being driven - range from 1.2- to 2-litre models. In Singapore, there are 662 Volkswagens affected, mostly the Touran TDI and Caddy light van.

VW is working out a plan to rectify the affected vehicles. Mr Diess says that for the 2-litre engine, it will probably involve a software modification. But for the smaller engines, some hardware changes will have to be made.

How will the cars be affected by the rectification? He would say only that for those that need a software modification, fuel consumption will not be affected.

Going forward, he adds, Volkswagen has decided to equip all diesel cars with selective catalytic reduction (SCR) "as soon as possible". SCR uses a purified urea solution called AdBlue to neutralise nitrogen oxides. In percentage terms, it costs more in small cars than in bigger models.

Mr Diess says "we still believe in the future of diesels". But he reveals that VW will now produce more electric models. The next Phaeton flagship limousine, for instance, will be available only as an electric model.

But for the moment, he says, "the focus is really to fix the problem with the customers and then to start rebuilding the trust and confidence in the company".

• The writer is editor of Torque, a motoring monthly published by SPH Magazines.