FRANKFURT (Reuters) - Volkswagen's <VOWG_p.DE> brand chief, Herbert Diess, is not planning to resign even though he is the subject of investigation by public prosecutors, he told a German newspaper.

The carmaker said late last month that prosecutors in Braunschweig were investigating Diess as part of a probe into whether Europe's carmaker violated disclosure and market manipulation rules by taking too long to inform investors it had cheated emissions tests.

"It's not up for debate," Diess told Sueddeutsche Zeitung in an interview published on Monday, when asked if he had thought about stepping down as a result of the probe.

He added the investigation had taken him by surprise and that he had first heard about it when asked by the media.

Volkswagen's reputation will take 12-18 months to recover from the crisis, although a strategic turnaround will take up to 14 years, Diess added.

The company needed to shift its strategic focus to employ more information technology and battery experts, Diess said. The shift would take "two vehicle generations" to be implemented, he said. Modern cars have a lifecycle of around seven years. "We must become more efficient, or else we won't be able to afford the transformation," he added.

(Reporting by Victoria Bryan, editing by David Evans)