Frankfurt, Germany / Detroit, Michgan - Volkswagen has halted sales of some 2015 diesel cars in the United States after regulators found software it designed for the affected vehicles gave false emissions data.
Chief executive Martin Winterkorn said on Sunday, "I personally am deeply sorry that we have broken the trust of our customers.
"Volkswagen has ordered an external investigation of this matter. We do not and will not tolerate violations of any kind of our internal rules or of the law."
He added that the company was fully cooperating with the relevant agencies but gave no details on who would carry out the external investigation.
On Friday the US Environmental Protection Agency charged Volkswagen with manufacturing vehicles designed to evade government pollution controls, saying the software deceived regulators measuring toxic emissions and adding that the automaker could face fines of up to $18 billion as a result.
Volkswagen dealers in the United States still have some 2015 diesel Jetta, Passat and Beetle cars for sale.
Bernstein analysts wrote in a note on Sunday: "This is not your usual recall issue, an error in calibration or even a serious safety flaw.
"There is no way to put an optimistic spin on this - this is really serious."
‘DEFEAT DEVICE’
The feature, which the EPA called a "defeat device," masks the true emissions only during testing. When the cars are on the road, they emit as much as 40 times the level of pollutants allowed under clean air rules meant to protect public health.
EPA enforcement officer Cynthia Giles said on Friday the cars in question "contained software that turns off emissions controls when driving normally and turns them on when the car is undergoing an emissions test".
"Using a defeat device in cars to evade clean-air standards is illegal and a threat to public health."
A Volkswagen spokesman said on Sunday: "We have admitted to it to the regulator. It is true. We are actively cooperating with the regulator.”
About 482 000 four-cylinder VW and Audi diesel cars sold in the United States since 2008 are involved in the allegations.
Volkswagen could face a civil penalty of $37 500 (R500 000) for each vehicle not in compliance with federal clean air rules. If each car involved is found to be non-compliant, the penalty could be $18 billion (R240 billion).
Both the EPA and the California Air Resources Board have launched investigations into the matter. The EPA has also referred the case to the US Department of Justice.
40 TIMES THE LEGAL LIMIT
The origin of the case was a report last year by the International Council for Clean Transportation and West Virginia University that documented elevated emissions from some Volkswagen cars.
The cars in question could emit as much as 40 times the legal standard of nitrogen oxide, the report said.
When regulators initially raised the issue with Volkswagen, the automaker blamed the elevated pollution on "various technical issues and unexpected in-use conditions."
In December 2014 it began a voluntary recall of about 500 000 cars, but regulators broadened their probe when the cars continued to pump out excess emissions after the recall, despite showing some improvement.
At that point, The EPA told Volkswagen it would not approve the company's 2016 models "until Volkswagen could adequately explain the anomalous emissions and ensure the agencies that the 2016 model year vehicles would not have similar issues.
"Only then did Volkswagen admit it had designed and installed a defeat device in these vehicles in the form of a sophisticated software algorithm that detected when a vehicle was undergoing emissions testing."