VW shares were once again the biggest losers on the Frankfurt stock exchange.
They closed 9.5 percent down to 100.45 euros after the firm said it had uncovered new anomalies -- this time in the carbon dioxide (CO2) emission specifications of engines in as many as 800,000 vehicles.
Of those, 98,000 were petrol-driven, German transport minister Alexander Dobrindt told parliament.
The announcement added a new dimension to an affair which has so far centred only on the group's diesel vehicles.
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Dobrindt said customers should not be expected to have to pay the higher tax if VW had deliberately understated the vehicles' CO2 emissions.
"We see it as VW's duty to ensure that customers face no additional costs," he said on the n-tv news channel.
VW has lost nearly 40 percent in market capitalisation since September, when the cheating revelations broke.
Until now, the scandal had centred on so-called defeat devices, sophisticated software fitted into diesel engines to skew the results of tests for nitrogen oxide emissions.
Tackling CO2 is becoming a rising priority in many countries, especially in Europe, where cars are often taxed according to their carbon emissions.
Late yesterday, the auto giant said an internal probe had uncovered "inconsistencies" on carbon emissions as well, affecting not only diesel engines but petrol engines, too.
"When will this litany of lies end?" asked Greenpeace campaigner Daniel Moser.
He called on governments and regulators to "end this continued deception and ensure Volkswagen upholds emissions standards."
These turn on pollution controls when cars are undergoing tests and off when they are back on the road, allowing them to spew out nitrogen oxide at excessive levels.