Volkswagen's promise to fix pollution control systems on about 11 million diesel vehicles could involve changes to software, and possibly hardware, that would increase fuel-consumption, reduce performance or require more maintenance.
A former executive of Volkswagen's US operation said on Tuesday the company might only have to change software to bring older diesel models into compliance with US emissions standards.
Other experts and US regulators said it would probably have to come up with two sets of solutions for two different emission-control systems installed on 482 000 US diesel cars from model years 2009-2015.
Volkswagen has admitted using software that circumvented US and California pollution rules, by fully activating the exhaust scrubbing systems only when the car was being put through precisely prescribed government emissions tests.
That meant the cars were able to pass laboratory tests that showed they met the relevant regulations, but then switched off the emission control devices while driving.
VW began installing the illegal software in late 2008 on two-litre, four-cylinder turbodiesel engines fitted with devices known as “lean NOx traps,” designed to reduce nitrogen oxides - linked to smog, acid rain and lung cancer - in engine exhaust.
Any device used to control nitrogen oxide emissions typically “diminishes the performance and fuel economy” of diesel engines, according to automotive consultant Sandy Munro.
Marc Trahan, who retired in late 2014 as executive vice president of group quality, after a 35-year career with VW and Audi, said older Volkswagen diesels could be made to function properly with a software fix; they shouldn’t need to have newer hardware installed, which would take much longer, require extensive “re-engineering” and be cost-prohibitive, he said.
From 2012, however, Volkswagen offered the same two-litre TDI engines with a more sophisticated and expensive emissions control system called Selective Catalytic Reduction, which injected a liquid urea solution into the exhaust to break down the nitrogen oxides.
The solution is supposed to be replenished every 15,000km by a dealer, but VW encountered potential problems.
Trahan said there were concerns within the company about the urea consumption being so great that it would require separate “fill-ups” every 8,000km, rather than the desired 15,000-km intervals that are typical between engine oil changes.
