VW chairman of the board of directors Hans Dieter Potsch says a chain of errors led to the emissions scandal and that its top priority is winning back trust.

Speaking at a news conference, Hans Dieter Potsch said: “We are talking here not about a one-off mistake but a chain of errors.”

He said Volkswagen would be “relentless in seeking to establish who was responsible” for the scandal.

VW CEO Matthias Muller said it was “fighting for every customer”.

However, he said a massive slump in sales had not occurred in the wake of the scandal.

In September, US regulators found some VW diesel cars had a “defeat device” – or software – to cheat emissions tests.

The automaker said the problem began when it decided to launch a large-scale promotion of diesel vehicles in the US in 2005, but found it impossible to meet strict emissions limits in force in that country in time.

VW said it had agreed steps to improve supervision of engine software development to prevent future manipulation.

Matthias Mueller said it was relatively simple and inexpensive to fix the millions of affected cars, but this had not been possible before, as the technology for the fixes was not available when the cars were built. In any case, the company was unaware at the time that there was a problem.

VW will in future undertake “real-life” tests, which will be checked by both internal and external third parties.

Hans Dieter Potsch said: “No business justifies crossing legal and ethical boundaries.”

He said it was likely that only a limited number of people took part in the deception and said they would not be named as yet, adding that it was impossible to stop misconduct by individuals.

However, he added that the actions taken by the company would make such actions that much more difficult in future.

Law firm Jones Day is conducting an investigation into what happened. That, Hans Dieter Potsch said, was making good progress, but would take some time to conclude.

The cheat device affects up to 11 million VW cars worldwide.