"We are definitely convinced that [the emissions systems] will work," Struth said this month at the Consumer Electronics Show here. The emissions "targets in Europe can be achieved only with the help of diesel engines, and the same is true in the United States."
Struth added that American diesel owners typically are repeat customers. "Guys that buy diesels are very loyal customers," he noted. "They love the diesel engine. It has great torque and great fuel economy. They know what they have."
With estimated global original-equipment parts sales of $44.24 billion in 2014, according to the Automotive News list of top suppliers, Robert Bosch GmbH of Stuttgart is the world's biggest automotive supplier. The company is a major producer of diesel fuel systems and engine control units.
The EPA has asked Bosch whether it knew that VW had tampered with the software of Bosch-produced engine control units used in 600,000 vehicles sold in the United States.
The engine control units allowed Volkswagen's vehicles to pass EPA emissions tests in the lab but disabled their catalytic converters and other emissions-control systems during normal road use.
Volkswagen has been reeling since it acknowledged in September that some 11 million diesel vehicles worldwide were equipped with such "defeat devices." Martin Winterkorn resigned as CEO, other top executives have left the company, and VW has been hit with lawsuits and investigations by regulators. So far it has set aside more than $7 billion to cover the costs of the scandal.
Struth said Bosch is cooperating with the U.S. investigation. "We are disclosing and delivering the information that has been requested," he said. "We are in the midst of an investigation" to find out what was known about the rigged emissions tests. "We have not made any conclusions."
While Struth seemed hopeful that the U.S. diesel market will recover, a top executive at Continental AG -- No. 3 on Automotive News' global supplier list -- was more downbeat.