California regulators Wednesday again rejected Volkswagen’s plan to fix diesel cars that were programmed to cheat on air pollution tests, saying the proposal lacked enough detail for the state to gauge its effectiveness.

The California Air Resources Board, which helped uncover the cheating last year, sent a letter to Volkswagen executives saying the plan’s details are “incomplete, substantially deficient, and fall far short of meeting the legal requirements” to ensure that the cars follow the state’s pollution regulations.

A Volkswagen spokesman could not be reached for comment Wednesday.

In February, the board rejected the repair plan submitted by Volkswagen that month covering diesel cars with 3-liter engines sold under both the VW and Audi brands in California starting in 2009. The board on Wednesday sent a similar letter to executives at Porsche, because Audi built 3-liter diesel engines for some Porsche models.

Volkswagen’s recall and repair plan would have covered about 16,000 cars in California, according to the board. It would not have affected Volkswagen cars with 2-liter diesel engines. Last month, the company agreed to a $14.7 billion settlement in which it would buy back or repair 2-liter diesel cars programmed to cheat on pollution tests.

And on July 6, California Attorney General Kamala Harris announced that the company would also pay $86 million in civil penalties to the state, in an agreement that covered both 2-liter and 3-liter cars. Volkswagen sold or leased an estimated 86,000 diesel cars in California equipped with cheating software.

California and federal officials last year accused Germany’s Volkswagen of programming its “clean diesel” cars to turn on all of their air pollution controls only when the cars detected a pollution test under way. With normal driving conditions, the cars emit up to 40 times as much nitrogen oxide as regulations allow, adding to smog.

In rejecting Volkswagen’s latest plan, the board 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.

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David R. Baker is a San Francisco Chronicle staff writer. Email: dbaker@sfchronicle.com Twitter: @DavidBakerSF