FRANKFURT, Germany (AP) — Volkswagen shares are falling after the company said it had understated carbon dioxide emissions for 800,000 cars, widening its scandal over cheating on U.S. diesel emissions tests.

The company's ordinary shares slid 9.7 percent Wednesday to 100.80 euros in morning trading in Europe.

The carmaker said Tuesday after the European market close that it found "unexplained inconsistencies" in carbon dioxide emissions in some vehicles. The company found the additional problem as it investigated revelations that up to 11 million of its vehicles had software that allowed them to deceive emissions testers.

The company has so far been unable halt the flow of negative surprises since the scandal first became known Sept. 18, when the U.S. Environmental Protection Agency announced Volkswagen had installed software on 482,000 cars that enabled them to cheat on emissions tests. The software would reduce emissions when the car was placed on a test stand, and then allow higher emissions during normal driving.

The announcement follows U.S. allegations that the defective software was also found in some cars with larger engines, including Volkswagen's elite Porsche brand.

CEO Matthias Mueller has promised the company will "relentlessly and completely clarify the matter." He has said the company must re-examine its corporate culture to prevent such missteps from occurring again.

The news that Porsche vehicles also had the deceptive software was an embarrassment for Mueller, who headed Porsche before he became CEO.

Mueller has said that upper management would not have involved itself in the details of software development and has pointed to "a few" employees who altered the software code. The company has hired law firm Jones Day to investigate.