BERLIN -- Germany's Volkswagen, already reeling from a scandal over cheating on U.S. tests for nitrogen oxide emissions, said Tuesday that an internal investigation had revealed "unexplained inconsistencies" in the carbon dioxide emissions from 800,000 vehicles.
It said fixing those vehicles could cost the company another $2.2 billion on top of the $7.4 billion it has already put aside to deal with recalling vehicles equipped with software that enabled them to cheat on nitrogen oxide emissions tests.
The revelation comes after VW's admission in September that it rigged emissions tests for four-cylinder diesel engines on 11 million cars worldwide, including almost 500,000 in the U.S.
It was not immediately clear whether the 800,000 vehicles with the newly discovered carbon dioxide emission problems were among those already affected.
Volkswagen did not identify which models were affected. It did say the 800,000 were "predominantly vehicles with diesel engines," raising the possibility for the first time that some Volkswagens with gasoline-powered motors may also have emissions problems.
A VW spokesman did not immediately return a phone call seeking clarification.
CEO Matthias Mueller, who took over from Martin Winterkorn, who resigned because of the emissions scandal, promised in a statement that Volkswagen "will relentlessly and completely clarify what has happened."
"It is a painful process but for us there is no alternative," he said. "For us only one thing counts, and that is the truth."
Volkswagen's board of directors said in a separate statement that they learned of the development "with dismay and concern." "The board of directors and the committee specially established to investigate will meet soon to discuss further measures and consequences," it said.
The investigation that revealed the inconsistencies in the carbon dioxide emissions was undertaken by Volkswagen after the revelations of its cheating on U.S. nitrogen oxide testing. The company assured customers that the safety of the vehicles in question "is in no way compromised."
It said Volkswagen "will endeavor to clarify the further course of action as quickly as possible and ensure the correct CO2 classification for the vehicles affected" with the responsible authorities.
In talks with the authorities — whom Volkswagen did not identify — the company said it hoped to come up with a "reliable assessment of the legal, and the subsequent economic consequences of this not yet fully explained issue."
The news broke after Germany's DAX was closed for the day, but Volkswagen shares ended down 1.51 percent to 111 euros.
In another blow to the legendary automaker, the U.S. Environmental Protection Agency said Monday that it had discovered that VW also installed secret software in vehicles with a larger, 6-cylinder diesel engine to hoodwink emissions tests. That would extend the issue to more Volkswagen modes and to some Audis and Porsches.
The automaker denied that accusation.