It’s back to the drawing board for Volkswagen when it comes to finding an adequate fix for thousands of vehicles equipped with emissions cheating defeat devices in California, as state regulators rejected the carmaker’s remedy proposal. 

The California Air Resources Board (CARB), which uncovered VW’s emissions cheating ways with the Environmental Protection Agency in Sept. 2015, determined that the carmaker’s recent proposal to fix about 16,000 3.0 liter VW, Audi and Porsche vehicles lacked enough detail to be deemed effective.

In a letter [PDF] sent to VW on Wednesday, CARB said the plans were “incomplete, substantially deficient, and fall far short of meeting the legal requirements to return these vehicles to the claimed certified configuration.”

Among the issues CARB found in the proposal were VW’s failure to fully describe all defeat devices used in the vehicles, and 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.”

The board also said the company had not shown how much its proposed fixes would lower pollution levels for each car as well as affect fuel economy, performance, and safety.

“CARB, in conjunction with EPA, will continue the on-going technical discussions with the companies through the enforcement process to ensure a legally and technically acceptable resolution is reached which fully mitigates the excess emissions,” the board said in a statement.

If this all sounds familiar, that’s because it is. Back in January, CARB rejected VW’s first attempt to provide a remedy for hundreds of thousands of 2.0L diesel-engine vehicles citing similar issues.

Specifically, the 2-liter vehicle remedy proposal failed to adequately identify and describe the affected vehicles; provide a sufficient method for obtaining owners’ names, address, and related information; describe the remedial procedure for affected vehicles; contain the impact of proposed fixes on fuel economy, drivability, performance, and safety, among other things.

Wednesday’s rejection comes just weeks after VW agreed to pay about $15 billion to begin the long process of putting the diesel scandal—which included vehicles that emitted 40 times the allowable rate of nitrogen oxide into the environment—behind it.

According to the 225-page settlement [PDF], VW will pay a maximum of $10.03 billion to cover buybacks and fixes for the affected vehicles, $2 billion to invest in green energy funds, and $2.7 billion to offset diesel emissions.

The deal requires VW to buy back or fix affected diesel-engine vehicles, and provide additional compensation to owners.

[via SFGate]