The board claimed that the plans submitted by all three companies were “incomplete and deficient in a number of areas”, and that ongoing technical discussions will need to be had before an agreement can be made.
Volkswagen has responded in an offical statement, saying: “We understand that today's announcement from CARB is a procedural step under California state law and relates to recall plans for vehicles with V6 3.0-litre TDI engines that were submitted previously.
"We continue to work closely with the U.S. Environmental Protection Agency (EPA) and CARB to try to secure approval of a technical resolution for our vehicles as quickly as possible.”
Models affected by the decision are those that use Volkswagen’s 'generation 2.1' and '2.2' V6 diesel units, such as the Volkswagen Touareg (pictured above), Porsche Cayenne and Audi A8 built between 2009 and 2016.
An estimated 85,000 vehicles use these engines across the US, with a significant percentage residing in California.
Volkswagen has previously said that ‘fixing’ all of these vehicles would not be complicated, but this latest development has lead some to suggesting the car maker may be forced to buy back all of the cars if an agreement can’t be made.
Just last month Volkswagen agreed to spend more than $1 billion (about £757 million) to remedy issues created by its emissions cheating software. CARB said the money includes about $380 million for projects to encourage the use of cleaner heavy-duty vehicles, and £800 million for investment into California’s zero-emissions programmes.