THINGS are going from bad to worse at beleaguered car manufacturer Volkswagen, which has been forced to admit the emissions scandal has widened to include petrol vehicles for the first time.

The once beloved German brand is currently facing the biggest scandal in its 78-year history after environmental tests forced the company to admit diesel cars had software installed that would help them run cleaner during government testing.

Now, the company has revealed an internal investigation found that 800,000 more vehicles showed “irregularities” on carbon emissions including petrol engines for the first time.

“ ... During the course of internal investigations irregularities were found when determining type approval CO2 levels,” the company said in a statement.

“Based on present knowledge around 800,000 vehicles from the Volkswagen Group could be affected. An initial estimate puts the economic risks at approximately $3.04 billion (€2 billion).”

That number could rise much higher once the full scale of the problem is known. CEO Matthias Muller said the company is committed to the “painful process” of finding out the truth.

“We will stop at nothing and nobody. This is a painful process, but it is our only alternative. For us, the only thing that counts is the truth. That is the basis for the fundamental realignment that Volkswagen needs,” he said.

The news caused shares to plummet on Wednesday to around 10 per cent lower than the day before.

In a separate move, Porsche SE, the investment company which owns 32.4 per cent of VW’s capital, said the fresh revelations could have a “negative impact” on its own results, although it maintained its projections for 2015.

Porsche’s North American subsidiary announced it was suspending sales of its Cayenne diesel vehicles until further notice, but stressed that customers could continue to operate their crossover cars.

Among the engines affected are 1.4, 1.6 and 2.0 litre motors of VW, Skoda, Audi and Seat vehicles, said a VW spokesman, adding that these cars had been found to be releasing more of greenhouse gas CO2 than previous tests had shown.

At least one petrol engine is concerned, the company said in a revelation that expands the scandal beyond the initial diesel engines.

In September the company admitted 11 million of its diesel vehicles contained the devices designed to cheat official pollution tests, which sparked global outrage and investigations.

The so-called defeat devices turn on pollution controls when cars are undergoing tests and off when they are back on the road, allowing them to spew out harmful levels of nitrogen oxide.

The latest issue opens up another front in the scandal engulfing the company as it relates to a different type of engine and emissions.

It also comes a day after US authorities accused the carmaker of also fitting the nitrogen oxide defeat devices on its larger 3.0 litre diesel vehicles including various six-cylinder 3.0 litre diesel VW Touareg, Porsche Cayenne and Audis, charges VW adamantly denied.

The inclusion of Porsche vehicles among those alleged to contain defeat devices could trip up Mr Mueller, who was drafted in from the luxury sports car unit to replace Martin Winterkorn, who resigned at the height of the scandal.

“We have clear evidence of these additional violations,” said Cynthia Giles, an official with the US EPA’s Enforcement and Compliance Assurance office.

“VW has once again failed its obligation to comply with the law that protects clean air for all Americans.”

Mr Mueller did not address the latest US allegations in his latest statement. However the

world’s number two carmaker by sales, had swiftly denied the new US charges.

“Volkswagen AG wishes to emphasise that no software has been installed in the 3-litre V6 diesel power units to alter emissions characteristics in a forbidden manner,” it said in a statement.

“Volkswagen will co-operate fully with the EPA (to) clarify this matter in its entirety.”

Porsche similarly denied the allegations, insisting that “all of our information was that the Porsche Cayenne Diesel is fully compliant.” Audi, another of VW’s high-end brands, insisted that the software installed in its engines were “in line with the law.” It argued that the so-called Auxiliary Emission Control Devices (AECD) fitted into its engines were not designed to cheat pollution tests, but maximise the engine’s performance under different driving conditions.

Carmakers were allowed to fit AECDs in cars in the United States as long as they kept the authorities informed once a year, a spokesman explained.