The boss of Volkswagen US has admitted he was told in early 2014 about a "possible emissions non-compliance" at the company.
Michael Horn, the CEO of Volkswagen Group of America, has also apologised for the German carmaker's actions, describing them as "deeply troubling".
The apology and details about what Mr Horn knew of the emissions cheating are revealed in testimony he will present later today to a House Committee investigating the scandal.
"I did not think something like this was possible at the Volkswagen Group," he says in the written testimony.
"We have broken the trust of our customers, dealerships, and employees, as well as the public and regulators."
Mr Horn said he was made aware of the "possible emissions non-compliance" following the publication of a West Virginia University study in spring 2014.
He said: "I was informed that EPA regulations included various penalties for non-compliance with the emissions standards and that the agencies can conduct engineering tests which could include 'defeat device' testing or analysis.
"I was also informed that the company engineers would work with the agencies to resolve the issue.
"Later in 2014, I was informed that the technical teams had a specific plan for remedies to bring the vehicles into compliance and that they were engaged with specific agencies about the process."
Mr Horn said the company takes "full responsibility for our actions and we are working with all relevant authorities in a cooperative way".
He added that VW is "determined to make things right" in the wake of the scandal.
Last month VW was forced to apologise after it was discovered that it had developed software to trick emission tests for some of its diesel models.
The devices are able to detect when cars are undergoing tests, and can switch the vehicle to a low emission mode in order to achieve more favourable results.
This means that many people have bought cars which are less environmentally friendly than they were led to believe.