Audi is offering a free software upgrade for 850,000 diesel cars to improve their emissions performance.

The carmaker said the retrofit programme is for cars with six-cylinder and eight-cylinder diesel engines in Europe and other markets outside the US and Canada.

The upgrade is expected to “further improve their emissions in real driving conditions beyond the current legal requirement”.

It also applies to the Porsche and Volkswagen models that are fitted with the same type of engines.

The move comes in the wake of the Volkswagen scandal, which saw the German carmaker fined by the US Environmental Protection Agency (EPA) for falsifying emissions tests.

The company said: “Audi aims to maintain the future viability of diesel engines for its customers and to make a contribution towards improving air quality.

“At the same time, Audi is convinced that this programme will counteract possible bans on vehicles with diesel engines. With their low fuel consumption, diesel engines help to achieve the ambitious CO2 targets in Europe, which is another reason why Audi has decided to offer this retrofit programme.”

Audi is still under investigation by the German Federal Motor Transport Authority (KBA) for potential emissions irregularities in some of its vehicles. The carmaker however said it has been “intensively examining” all diesel engines.

It added: “If those investigations result in further consequences, Audi will of course quickly implement the required technical solutions in the interest of its customers as part of this EU5/EU6 retrofit programme.”

Daimler is also voluntarily recalling three million Mercedes-Benz cars with diesel engines in Europe to improve their emissions performance.

Volkswagen, Daimler and BMW have been accused of colluding on technology for decades.