Daimler will issue a voluntary service action for more than 3 million of its cars in Europe to add a free emissions fix - a process it hopes will “strengthen confidence” in customers.

The brand, which has recently denied allegations in Germany that it has been cheating emission tests, said its service action provides customers with the option to have new software for cars running with OM 607 turbocharged 1.5-litre four-cylinder diesel engines, which are used in Mercedes A-Class and B-Class models, to lower their output of nitrogen oxide.

It said the process, due to cost about 220 million euros, is being “carried out in close cooperation with the German regulatory authorities” and allows engineers to add newer, more effective technology to the existing EU5 and EU6 engines. The process will take about one hour per car, with the first cars receiving updates in the coming weeks. The final cars are predicted to be completed late in 2018.

The latest emissions fix plan expands a process that has seen the issuing of new software for a quarter of a million compact Mercedes models since March, of which 45% of affected cars have already received the change. The brand has also carried out a voluntary service action for the V-Class van, where 75% of customer vehicles have been worked on.

Daimler said it will also plans to commence the "rapid" roll out of a new diesel engine family that will be more efficient and cleaner than the current range.

The brand's diesel technology was called into question last week when German Transport Ministry officials met with Daimler representatives, including head of technology development Ola Kaellenius, to discuss accusations that it has used software to improve the results of its diesel models in emissions tests.

Daimler responded in an official statement, saying "On the basis of our current information, we would fight any claim by the German Transport Safety Authority (KBA) that we installed an illegal emissions control device with all legal means available".