'Conscious breach of US law'

Deutsche Welle: How common is it to find devices in cars that do things without our knowing about it, such as with...?

Ferdinand Dudenhöffer: I'm not sure how common it is. But what you have is an engine control unit (ECU), which is highly complex and which can detect test cycles. It's hard to say whether other companies install "defeat devices," such as the Americans forbid, but I would say probably not.

How do defeat devices work?

It's relatively easy to detect a test cycle, because you've got a very specific procedure as to what demands are placed on the engine [during a test phase]. It's impossible for humans to recreate the exact procedure as it's carried out by the computer to test the engine. In Europe, the test cycle takes 20 minutes, and already after 2 minutes, the ECU can tell that a test cycle is running. So the test cycle is detected very quickly. And once it's been detected, the car can shift accordingly, so that it runs with less horsepower, lower performance, that you throttle the engine, make it cleaner, and release fewer emissions.

And these test cycles are required by law...

Yes, they're required by law. It's a bit different in the US as here in Europe. In Europe it's called the New European Driving Cycle (NEDC) and it's conducted in a laboratory. The car is placed on a dynamometer and drives for 20 minutes in a defined fashion - it moves through the gears, then drives steady for a while at 80 kilometers per hour, then, for instance, it drops to 50 kilometers per hour, and all this happens according to standardized durations and processes, so basically it's a computer program driving the car.

So according to the European standard, you would know your car is being tested?

Well, no, because this is done by the manufacturer, before the car is certified for the roads. So the customer has no knowledge of the test. This homologation process is one step through which the emissions of a vehicle are determined, and its usage, and it's done with this test. In America, it's a little different, but the principle of the method is the same.

How would the defeat device have been detected in the Volkswagen cars in the US?

You would only detect it through meticulous investigation. If you found time series which appeared suspicious, you would take a closer look and try to re-drive the test cycle, take new measurements, and then you would repeat the process again but alter the test within the computer program just a little and cross-check the results… It takes a lot of detailed work to be sure that someone has cheated.

So what should happen now in the case of Volkswagen in America?

Well, the American environmental agency has already done it... They have ordered VW to recall the cars and re-fit them so that they fulfill the environmental standards. They are also threatening VW with fines, but there are no specifics as yet. As far as I'm concerned, now, VW still has to explain what's happening outside of the US - American law is quite strict and elsewhere it's relatively mild. And I would have expected VW CEO Martin Winterkorn to have assured all customers outside of the US this morning [21.9.2015] that their cars have not been fitted with one of these defeat devices, and as such meet all legal requirements on emissions. But he didn't do it.

What does that mean for you? Should he resign?

It doesn't mean much. But I was surprised that despite the situation, he did not make this assurance. I expect the head of a company to speak clearly and make clear how well his cars meet the legal requirements.

But do you think VW was aware that what it was doing was cheating?

They had to be aware, because VW knew what US law required, VW knew what defeat devices are. So I would say it was a conscious breach of US law. It couldn't have happened by accident.

Ferdinand Dudenhöffer is the director of the Center for Automotive Research (CAR) at the University of Duisburg-Essen in Germany.