Hard on the heels of the diesel emissions scandal, Volkswagen has come forward with new data discrepancies relating to CO 2 levels

Has Volkswagen been rigging CO2 emissions tests as well as diesel emissions?

That is the implication of the oblique statement released by the German carmaker on Tuesday. VW said it found “irregularities” and “unexplained inconsistencies” in the levels of carbon dioxide emitted by its cars. It admitted that CO 2 levels and fuel consumption figures for some models were set too low during the testing process.

There were no details about why this happened – such as whether another defeat device was used – or the scale of the irregularities. Indeed, VW said the issue was “not yet fully explained”.

However, no matter how it was done, if CO 2 emissions were artificially lowered during testing with technology that was not declared to the authorities or does not work the same way on roads then this counts as cheating tests.

What Volkswagen cars are affected?

About 800,000 VW vehicles are involved. However, the company says this is just an estimate based on current knowledge.

The specific models have not yet been officially declared. However, the company has indicated the vehicles have 1.4-litre engines and are mostly Polos and Golfs, although some are Audi, Seat and Škoda cars.

The majority have diesel engines, but this means for the first time that petrol engines are involved in the emissions rigging scandal.

In terms of geography, the German government has said a quarter of the cars are in that country, but that is all that is known so far.

How was the latest scandal uncovered?

Volkswagen said it uncovered the problem during its internal investigation into the diesel emissions scandal that began in September.

It is not clear whether the 800,000 cars involved are part of the 11m VW has admitted were fitted with a defeat device to cheat nitrogen oxide tests, or are a new set of vehicles. The fact that some of the cars involved have petrol engines suggests the latter.

How serious is this latest discovery?

Very. Volkswagen has said the “economic risks” are €2bn (£1.4bn). This works out as €2,500 per car, far more than the €609 per car put aside for the cost of the 11m cars involved in the diesel emissions scandal.

Analysts believe these costs mainly relate to the amount VW will have to pay back to governments in tax credits. CO 2 emissions are used to set the road duty that vehicles are eligible for, so rigging the tests would mean VW vehicles contributed less in tax than they should have.

However, this may only be the start of the costs. VW may have to compensate owners upset that their car consumes more fuel than they thought. This cost is relatively easy for motorists to calculate, because they will be able to work out the total mileage of their car and the difference between the stated fuel economy of their vehicle and its performance.

The latest revelation could also have a more damaging impact on the brand than the diesel emissions scandal, because it directly relates to the performance of the vehicle.

Shares in VW fell by 10% on Wednesday, with investors in the company clearly spooked about the potential costs.

Is this linked to Environmental Protection Agency making new allegations against Volkswagen in the US?

No. On Monday, the EPA issued a second notice of violation of the Clean Air Act to VW, claiming that the company used defeat devices in VW, Audi and Porsche vehicles with three-litre diesel engines.

The EPA uncovered the initial emissions rigging scandal at VW, but that involved cars with smaller engines. The carmaker has denied using defeat devices in the three-litre vehicles, but is cooperating with the EPA inquiry.

What should Volkswagen drivers do now and will there be a cost?

VW has said all the 800,000 vehicles are safe and legal to drive, so motorists should carry on as normal for now.

VW drivers with one of the 11m vehicles affected by the initial diesel emissions scandal have already been contacted by post and are awaiting details about how the defeat device will be removed. It is likely that VW will eventually formally contact motorists affected by the latest development too, but the company is still attempting to get to the bottom of what has actually happened and what models are involved.

Whether the affected cars will need to be repaired is unclear, because there is no absolute upper limit on CO 2 emissions.

Governments in Europe have already said that VW itself should pay any shortfall in tax income if it turns out that their vehicles were in the wrong tax bracket because they cheated CO 2 emissions tests.

However, motorists would be able to claim compensation if it turns out their vehicle consumed fuel at a quicker rate than they thought.