In an effort to reduce their nitrogen oxide (NOx) emissions, Mercedes-Benz has voluntarily recalled over three million diesel cars across Europe and hundreds of thousands in the UK. The recall is not being done for safety or scandal reasons; it is more of a pro-active decision, according to the company, to have more clean vehicles driving the roads.

Nitrogen oxide can be harmful to the environment and to people's health as the gas can create smog and acid rain. In performing the upgrades to the electronic control unit (ECU) in the vehicle's engine, Mercedes-Benz can reduce their negative effect on the environment. Diesel engines are often seen as better for the environment overall as they have low cardon dioxide (CO2) emissions, a gas considered to be a primary factor in global warming.

The overall cost of the recall for Mercedez-Benz is expected to be £195 million, making it one of the most expensive voluntary recalls by a manufacture to reduce diesel emissions. This action, which began in March 2017, has also brought Daimler, the manufacturing company of Mercedes-Benz, under investigation to ensure they are not using similar technology as Volkswagon in the 2015 scandal called "dieselgate".

There are various models affected by this voluntary recall. Essentially all Euro5 and Euro6 diesel-engined cars sold between early 2011 and late 2015 are part of the recall group. The only confirmed exemptions are the E-class saloon with the two-litre turbodiesel engine and the S-Class V6 turbodiesel engine.

Vehicle owners will receive letters if they are affected. Those who own an affected vehicle can bring their Mercedes to a dealership and the engine upgrade will be done without cost to the customer. According to Daimler spokespeople, the software modification service is not expected to have any negative side-effects to the performance of the vehicle.