(CN) - Shares in Volkswagen plunged Wednesday after an internal investigation revealed "unexplained inconsistencies" in the carbon dioxide emissions from 800,000 of its vehicles.
The company estimated Tuesday that the new issue could cost $2.2 billion to resolve.
Shares in the company dropped by 8.4 percent just after the market opened on Wednesday morning.
The latest news adds a new dimension to the scandal that the automaker has been facing since September over the excess nitrogen oxide emissions from up to 11 million vehicles worldwide that have been fitted with software designed to cheat on emissions tests.
Carbon dioxide emissions depend on a vehicle's consumption rather than its emissions-control systems. The company has already set aside $7.4 billion to cover the costs related to the nitrogen oxide problems.
While Volkswagen did not specify in Tuesday's announcement which models the new issue affects, it did say the "majority of vehicles concerned have diesel engines." The allowance has given rise to speculation that some vehicles with gasoline-powered motors may also have emissions problems.
Matthias Muller, who replaced former CEO Martin Winterkorn after he resigned at the brink of the scandal this fall, promised that Volkswagen will push for the "relentless and comprehensive clarification of events."
"We will stop at nothing and nobody. This is a painful process, but it is our only alternative," Muller said. "For us, the only thing that counts is the truth. That is the basis for the fundamental realignment that Volkswagen needs."
In a separate statement, the Volkswagen Supervisory Board said it is "deeply concerned over the irregularities found when determining CO2 levels" and "will continue to ensure swift and meticulous clarification."
U.S. regulators have yet to address the automaker's admission that it may have understated fuel consumption and carbon dioxide emissions.
The scandal had already widened this week when the EPA announced on Monday that it found defeat-device software on thousands of larger 3.0 liter engines used in Volkswagen's luxury sport utility vehicles such as the Porsche and Audi.
Porsche's North America unit responded on Monday by saying that it was "surprised" to receive the EPA's notice of violation regarding the 2015 Porsche Cayenne Diesel.
"Until this notice, all of our information was that the Porsche Cayenne Diesel is fully compliant," Porsche said.
On Tuesday, Porsche announced that it would voluntarily stop sales of its model year 2014 through 2016 Cayenne Diesel vehicles until further notice.
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