LOS ANGELES (AP) — The Volkswagen Group of America submitted its proposal Tuesday to bring Porsches, Audis and Volkswagen cars with six-cylinder, 3.0-liter diesel engines up to California's air quality standards after state regulators found the vehicles were programmed to emit cleaner emissions on government treadmill tests than on the real road.

The California Air Resources Board confirmed it had received VW's plan, but the agency will not comment on any details until further review, said David Clegern, a spokesman for the board. The U.S. Environmental Protection Agency, which is conducting a parallel investigation for violations of federal clean air rules, said it had also received the plan.

The problem affects 85,000 cars with 3.0-liter diesel engines sold nationwide between 2009 and 2015, including some Porsche SUVs and Audis that are sold under the Volkswagen Group umbrella. Between 16,000 and 17,000 of those vehicles are operating in California, Clegern said.

In a statement, Audi spokesman Mark Clothier said the company is cooperating with authorities and hopes to have a resolution for car owners in the near future.

VW admitted last year to installing so-called 'defeat devices' on 2.0-liter diesel engines in some of its most popular models, including the Beetle, Jetta, Golf and Passat.

There are about 500,000 Volkswagen 2.0-liter diesel models on the road in the U.S. affected by that recall.

California regulators last month rejected a similar recall plan for those models as "incomplete and substantially deficient," prolonging the limbo for VW owners and leaving open the possibility of a buyback program.

Also last month, the U.S. Justice Department, representing the EPA, filed a civil suit that could potentially expose VW to more than $20 billion in fines under the Clean Air Act. VW could rack up additional civil penalties based on the facts determined at trial.

A separate criminal investigation is under way, and numerous private class-action lawsuits filed by VW owners are pending.

A number of states' attorneys general have also launched probes into the emissions scandal.