Two top Volkswagen engineers who found they couldn’t deliver as promised a clean diesel engine for the U.S. market are at the center of a company probe into the installation of engine software designed to fool regulators, according to people familiar with the matter.

The two men, Ulrich Hackenberg, Audi’s chief engineer, and Wolfgang Hatz, developer of Porsche’s winning Formula One engines, were among the engineers suspended in the investigation of the emissions cheating scandal that sank the company’s market value by 43% since September 18 and triggered a world-wide recall to refit the engines to meet clear-air standards, these people said.

Hackenberg and Hatz, who didn’t respond to requests for comment, are viewed as two of the best and brightest engineers in German industry. They were put in charge of research and development at the Volkswagen group shortly after Martin Winterkorn became chief executive in January 2007. Winterkorn, who resigned over the scandal, couldn’t be reached for comment.

The company has acknowledged that managers, struggling to meet U.S. sales targets, masked the emissions of new-car engines to sell so-called clean diesel technology to skeptical American consumers. The car maker said as many as 11 million vehicles carried a “defeat device,” software that reduces tailpipe emissions only when the car is being tested, not on the road.

Several countries have since blocked sales of certain VW vehicles, and regulators are considering steps to tighten emissions standards for diesel engines.

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