Volkswagen CEO Martin Winterkorn stepped down on Wednesday, taking responsibility for the German automaker's rigging of U.S. diesel emissions tests.

"Volkswagen needs a fresh start -- also in terms of personnel. I am clearing the way for this fresh start with my resignation," Mr. Winterkorn said in a statement. "I am shocked by the events of the past few days. Above all, I am stunned that misconduct on such a scale was possible in the Volkswagen Group," the embattled CEO said. "As CEO I accept responsibility for the irregularities that have been found in diesel engines and have therefore requested the Supervisory Board to agree on terminating my function as CEO of the Volkswagen Group. I am doing this in the interests of the company even though I am not aware of any wrong doing on my part."

Mr. Winterkorn's successor will be named Friday, VW said.

Mr. Winterkorn has been under heavy fire since revelations Friday that the company was cheating on tests by fitting its diesel vehicles with software that masked their real-world emissions, in violation of the U.S. Clean Air Act. The pressure intensified this week as the company announced that some 11 million vehicles worldwide had the illegal software.

As early as the beginning of this month, Mr. Winterkorn, 68, who had survived an earlier clash with former Chairman Ferdinand Piech, appeared to be on course to have his contract renewed through 2018.

His ouster puts into question a broad restructuring of the company that would have organized Volkswagen into four holding companies.

Under Mr. Winterkorn's leadership, VW was closing in on Toyota Motor as the world's biggest automaker, with the German manufacturer overtaking its Japanese competitor in global sales in the first half. VW's six-month sales amounted to 5.04 million cars and trucks, exceeding Toyota's 5.02 million deliveries. VW has a goal of becoming the No. 1 carmaker by 2018.

-Automotive News