Volkswagen's proposed US recall to correct excessive nitrogen emissions from its 2-litre diesel cars is inadequate, US environmental regulators said Tuesday.
The decision sends the German carmaker back to the drawing board for a US recall of nearly 500,000 2-litre diesel cars sold from 2009-15.
"Volkswagen made a decision to cheat on emissions tests and then tried to cover it up," said Mary Nichols, chairwoman of the California Air Resources Board (CARB). "They continued and compounded the lie, and when they were caught they tried to deny it."
The US Environmental Protection Agency said it "agrees with CARB that Volkswagen has not submitted an approvable recall plan to bring the vehicles into compliance and reduce pollution." The federal agency said it had previously informed VW.
VW chief executive Matthias Mueller is scheduled to meet Wednesday in Washington with US EPA chief Gina McCarthy.
On the sidelines of the North American International Auto Show in Detroit, VW said it was "committed to working cooperatively" with US regulators.
Despite the rejections, VW said it has had "constructive discussions" with CARB officials, including talks last week on a framework to remediate the diesel emissions issue.
The company said it is seeking to develop a "swift, fair and independent" recall and compensation programme to deliver "a comprehensive remedy for our customers."
In all, some 580,000 2- and 3-litre diesel cars sold in the US by VW and subsidiaries Audi and Porsche carried a so-called defeat device - software that lowered emissions when it sensed the car was undergoing testing.
Mueller said this week that VW might have to buy back more than 100,000 of those due to technical complications that make emissions reductions difficult on some models.
The scandal could be the most expensive in automotive history.
US authorities filed a lawsuit last week against VW over the emissions cheating. Penalties for environmental violations could theoretically reach 45 billion dollars, on top of billions of dollars to recall or buy back cars and litigate mounting consumer fraud lawsuits.
CARB had a key role in exposing software in VW diesels that made the cars falsely appear to comply with state and federal clean-air standards. Due to the size of the California market, carmakers and other manufacturers generally seek to meet the state's safety and environmental regulations on all US products.
VW is due to deliver a recall plan for 3-litre vehicles by February 2.
CARB said VW's 2-litre recall plan "fell short in several areas," with insufficient detail about proposed repairs for authorities to make a technical evaluation.
The VW proposals, which have yet to be made public but may include installation of a catalytic converter to reduce emissions, "do not adequately address overall impacts on vehicle performance, emissions and safety," CARB said in a statement.
The rejection does not apply to VW's 3-litre vehicles.
CARB on Tuesday further gave VW formal notification of 13 specific violations of California emission standards and other regulations.
"The defeat devices on VW's diesel vehicles have caused substantial excess, illegal, and ongoing emissions of nitrogen oxides from the vehicles," CARB said.
CARB noted that the rejection does not preclude an eventual VW recall and allows "for a broader array of potential remedies."