Volkswagen CEO Matthias Mueller said last weekend he believed a new catalytic converter could be fitted to most affected vehicles in a way that would satisfy regulators, but apparently this wasn’t enough.

According to the regulators, the recall plan was too vague and slow and it was not acceptable for various other reasons, such as inadequate information of the affected cars, lacked owners’ information, and also proper details of how this fixing will be beneficial in the future.

In a statement, VW said that, in the time since its latest proposal was rejected, VW has been involved in ongoing discussions with both the EPA and CARB. “It is important for him to make clear: Volkswagen’s apology for the breach of trust with the American people is meant sincerely and honestly”, it said.

On Tuesday, The California Air Resources Board or CARB said it notified Volkswagen Group of America Inc. that it is rejecting VW’s submitted recall plan for 2-liter diesel passenger vehicles sold in California between 2009 and 2015.

VW had said it would present a reworked plan to the EPA at today’s meeting. “Volkswagen made a decision to cheat on emissions tests and then tried to cover it up”, Mary Nichols, chairwoman of the state board, said in an emailed statement.

“Since then, Volkswagen has had constructive discussions with CARB, including last week when we discussed a framework to remediate the TDI emissions issue”, VW said in an emailed statement.

In comments aired by National Public Radio (NPR), Mueller blamed the scandal on a misunderstanding and called it a technical, not an ethical, problem.

It’s possible that they may need SCR systems to meet emissions standards, which could cost thousands of dollars per vehicle and greatly extend the duration of any recall. Mueller said the source of the dispute is variations between German and United States laws governing corporate documents. Volkswagen faces enormous fines and lawsuits globally as a result.

“They understand fully the order of magnitude of mistakes that have been made and my sense is they are very committed to resolving this in an appropriate way”, Corker said in an interview Tuesday, before the California board announced it had rejected VW’s recall plan.

The remarks, coupled with the time it has taken Mueller to visit the United States since being made CEO in September, drew criticism in the United States and raised fresh questions over Volkswagen’s handling of the crisis. The company has recently been found to have installed the devices on cars marketed under its Audi and Porsche brands. California spurned the automaker’s December recommendation for how to fix 2-liter diesel engines as “incomplete”.

No specific details about this plan have been released to the public but it has been confirmed that the marque’s planned solution applied only to the 2.0-liter diesel not the 3.0-liter diesel also embroiled in the scandal. “And we did it together and it was a default of VW that it needed such a long time”. Something tells us it’s not going to be anywhere near that easy in the US.