Washington : The CEO of Volkswagen Group of America apologised for the software that was installed in its diesel vehicles to deceive environmental regulators, but he said a handful of "individuals" were responsible for the trickery.
In a hearing before the US House Energy and Commerce Subcommittee on Oversight and Investigations, Michael Horn on Thursday said most of the affected vehicles would continue to emit excessive pollutants for at least a couple of more years.
The executive denied having any prior knowledge of the software, which detected when emissions testing was taking place and turned on emissions' controls only when the vehicles were being operated in a test laboratory.
When those same vehicles were being driven under normal conditions, the controls were turned off and they spewed up to 40 times the allowable amount of nitrogen oxide, which contributes to the formation of smog and acid rain.
The deactivation of emissions controls during normal driving can improve a diesel-fuelled car's performance, experts say.
Horn learned about the defeat devices on September 1 of this year, two days before VW admitted to the US Environmental Protection Agency that nearly 500,000 VW and Audi diesel vehicles sold in the US had the illegal software.
The vehicles in question were from the model years 2009 to 2015.
The EPA issued a notice of violation of the Clean Air Act to Volkswagen on September 18, when the scandal erupted.
Horn also cleared other senior officials of the German automaker of wrongdoing, saying the trickery was "not a corporate decision" and "a couple of software engineers... put this in for whatever reason".
The VW Group of America chief said cars covered by the allegations could be fixed by 2017 because the solution requires the installation of new equipment.
Volkswagen Group CEO Martin Winterkorn stepped down on September 23 even though he also said he did nothing wrong.
VW said 11 million vehicles worldwide were equipped with the illegal software.