It seems owners of Volkswagen diesel cars equipped with illegal "defeat device" software will have to wait longer for a recall to update their cars.

The plan submitted by VW in November to modify its 2.0-liter four-cylinder TDI diesel models has been rejected by the regulatory agencies that must approve those fixes.

The California Air Resources Board (CARB) said Tuesday that it had rejected the proposed plan. The U.S. Environmental Protection Agency (EPA) said it concurs.

DON'T MISS: VW Diesel Reality Check: Company, Regulators Still Far Apart On Modifications

Both CARB and the EPA must approve Volkswagen's plans before the company can proceed with a recall. The California agency made its decision after pushing back its own deadline for approval by a few weeks.

The proposed plans for the 2.0-liter cars "contain gaps and lack sufficient detail," a CARB press release said.

Plans rejected by CARB do not cover vehicles the 3.0-liter V-6 TDI powertrain. VW has until February 2 to submit proposals to remedy these vehicles.

2015 Volkswagen Golf TDI

2015 Volkswagen Golf TDI

In a letter formally rejecting VW's plans, the agency provided a long list of deficiencies, but identified three issues as the "most serious."

The proposal did not describe the emissions cheating issues in sufficient detail "for CARB to adequately understand them in the context of the recall plans," the letter said.

In addition, CARB felt Volkswagen did not describe the proposed modifications in enough detail for regulators to determine their potential effectiveness, or indeed their technical feasibility.

ALSO SEE: VW Gets More Time To Figure Out TDI Diesel Emission Update (Dec 2015)

Finally, CARB said the proposal did not sufficiently explain potential effects on "the engine, the vehicle's overall operation, and all related emission control technologies, including the OBD system."

The agency said it will continue its investigation as well as discussions with Volkswagen to find an acceptable solution.

For its part, Volkswagen appeared to take the setback in stride.

2014 Volkswagen Beetle TDI

2014 Volkswagen Beetle TDI

The rejection only addresses initial plans that were submitted in late November, the company said in an e-mailed statement.

"Since then, Volkswagen has had constructive discussions with CARB, including last week when we discussed a framework," the statement said.

The exact contents of the rejected plans were never made public, so it's unclear what VW hadproposed.

MORE: VW May Buy Back (Some) TDI Diesel-Cheating Cars In U.S.: Report

An estimated 325,000 of the 482,000 affected 2.0-liter TDI models do not have Selective Catalytic Reduction (SCR) emissions control systems.

It's possible that they may need SCR systems to meet emissions standards, which could cost thousands of dollars per car and greatly extend the duration of any recall.

That's led analysts--and many customers--to argue that VW should simply buy these cars back.

A recent report claims the company is considering that, but only for 115,000 of the affected cars.


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