DETROIT -- Volkswagen AG 's promise to fix pollution control systems on about 11 million diesel vehicles will involve changes to software, and possibly hardware, that could leave owners with cars that deliver diminished fuel economy and performance or require more maintenance, experts said Tuesday.
The German automaker's new CEO, Matthias Mueller, said Tuesday VW customers would need to have those diesel cars "refitted." The company did not specify what the refitting might entail. Some analysts have said the job could cost more than $6.5 billion.
A former executive of Volkswagen's U.S. operation said Tuesday the company may be required to change only software, and not hardware, to bring older diesel models now deemed illegal into compliance with U.S. emissions standards.
But other experts and U.S. regulators said the German automaker likely will have to come up with two sets of solutions for two different emission-control systems installed on 482,000 U.S. diesel cars from model years 2009-15.
VW has admitted using software that circumvented U.S. and California pollution rules by fully activating the exhaust scrubbing systems only when the car was being put through precisely prescribed government emissions tests.
VW hasn't said why it used the illegal "defeat device" to deceive regulators. But the results, at least in the short term, were beneficial: VW was able to pass laboratory tests that showed its U.S. diesel cars met the relevant regulations, but then switched off the emission control devices while driving.