A US judge has given Volkswagen one month to present a plan to fix diesel engine cars secretly outfitted with pollution cheat devices.

District Judge Charles Breyer, at a hearing in San Francisco, set a March court date for the German auto giant, and the US Environmental Protection Agency, to present the plan.

"By March 24th, when I plan to have the next hearing in this matter, I want a definite answer from Volkswagen and EPA whether or not they've achieved a resolution of these vehicles -- a remediation of these vehicles -- whether they can do so technologically and within the parameters that EPA believes acceptable to them," Breyer said, according to a transcript of court proceedings obtained Thursday by AFP.

Volkswagen faces potentially huge damages as a result of the scandal, after some 200 owners of VW, Audi and Porsche diesel owners filed a class-action lawsuit in San Francisco earlier this week.

The suit accuses the German auto giant of major damages to the environment and to owners of more than a half million of the cars sold in the United States.

Volkswagen has admitted the existence of the illegal cheat software on its cars, which limits the output of toxic nitrogen oxides to US legal limits during emissions test by regulators.

But when the vehicles are in actual use, the software allows them to spew poisonous gases at up to 40 times the permitted levels.

The suit said owners of the cars have suffered losses on the vehicles' value and also have suffered in discovering that they were emitting more pollution into the air than they thought they were.

It also estimated the damages to the health of Americans generally from the extra toxic gases in their air at $450 million.

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