"EPA and CARB will immediately begin evaluating the proposed software," the EPA said.

Earlier on Thursday, Volkswagen America President and Chief Executive Officer Michael Horn told a congressional oversight panel that the company has sought EPA approval to begin installing software fixes in January in the first of nearly 500,000, 2009-2015 vehicles that contain the defeat devices.

Volkswagen said the cars fall into three generations of vehicles. The most recent models, known as Generation 3, number around 70,000 and would be the first to receive a fix.

EPA described the 2012-2014 Passats as Generation 2 vehicles, which Volkswagen said number around 90,000. Horn told lawmakers that Generation 2 vehicles could begin to receive fixes around the middle of next year.

The oldest cars, 325,000 vehicles grouped as Generation 1, would require major changes including the installation of new hardware. No date has been set for those vehicles to begin receiving remedies.

(Reporting by David Morgan; Editing by Bernard Orr)