Late Wednesday evening, the California Air Resources Board rejected Volkswagen Group’s plan to fix 3.0L diesel Volkswagens, Audis, and Porsches that were discovered last year to be illegally circumventing the cars’ emissions control systems. In two letters (one addressing Volkswagen and Audi cars (PDF) and the other addressing Porsches (PDF)), CARB called the company’s recall plan “substantially deficient” and said VW Group submitted documents that “fall far short” of meeting standards that would bring the cars up to code.

It has been estimated that a total of 85,000 3.0L diesel Porsche, Audi, and Volkswagen cars are still on the road without a recall or a buyback plan. In June, VW Group proposed a massive settlement in which it would buy back almost 500,000 2.0L diesel vehicles and compensate owners and lessees with a cash award.

In CARB’s Wednesday letters to VW Group, the air regulator claimed that subsidiaries Audi and Porsche “failed to disclose and provide a complete description of all defeat devices” on the cars, even after CARB rejected an earlier plan in February and reminded the automakers of what they needed to submit to get CARB to approve a recall plan. CARB also said that VW Group didn’t describe in enough detail how the fix would work or how it would impact the car’s emissions after the fix.

Volkswagen, Audi, and Porsche "failed to specifically and completely describe the fixes in their proposed recall plan in a manner that allows CARB to adequately evaluate whether they could be successful or are even technically feasible or would not cause greater emissions deterioration,” CARB wrote.

The air regulator added that VW Group provided inadequate documentation about how the fix would affect fuel economy, drivability, and the On Board Diagnostics (OBD) systems in the cars. CARB also concluded that “the recall plan cannot be completed expeditiously,” which was another criteria for having a recall plan approved.

CARB is the only state-level air regulator in the country, and it has been working closely with the Environmental Protection Agency on the Volkswagen case. Its latest rejection of VW Group’s recall plans are surprising, given that the regulator and the automaker have had this exchange before. Although the defeat devices on 2.0L diesel cars were apparently different in nature from the defeat devices on 3.0L diesel cars, the requirements CARB asked VW Group to meet to get a recall approved were apparently not different in the two cases. In January, CARB rejected VW Group’s proposed fix for the 2.0L diesel engines, citing almost the exact same lack of documentation and disregard for the recall plan’s effect on the rest of the car’s operability.

The rejection of the recall plan is even more surprising given that in June, a Volkswagen lawyer told a district judge that he believed the company would be able to fix its 3.0L diesel cars and not have to buy them back. Now, it seems, a future without a buyback for 3.0L diesel engines is less certain.

“CARB, in conjunction with the EPA, will continue the on-going technical discussions with VW and Audi to evaluate their proposals through the enforcement action process,” the regulator’s letters to VW Group said. The automaker is expected to appear in Northern California District Court on August 25 to update District Judge Charles Breyer on plans to fix these remaining 3.0L diesel vehicles.

Update: In a statement to Ars, a Volkswagen spokesperson called the rejection "a procedural step under California state law."

"We continue to work closely with the US Environmental Protection Agency (EPA) and CARB to try to secure approval of a technical resolution for our 3.0L TDI vehicles as quickly as possible," the statement added.