After an event billed as the National Diesel Forum, involving Germany's top political leaders, the Volkswagen Group, BMW, Opel and Daimler (parent of Mercedes-Benz) have agreed to upgrade millions of diesel vehicles to cut their pollution output.

A majority of the Euro5 diesel cars in Germany and some Euro6 vehicles in the country will receive a free software upgrade, which the German automakers' association (VDA) says will reduce oxides of nitrogen (NOx) output by between 25 and 30 per cent.

The association claims "engine performance, fuel consumption [and] service life" will not be affected by the upgrades. The VDA says it's possible to reduce NOx output without any side effects due to "technical advances in exhaust gas aftertreatment and engine control, which have only been developed in recent years".

All up around five million cars will be upgraded with new software, although this includes 2.5 million Volkswagen Group cars that have "already been improved ... in recent months".

Revealing the automakers desire to head off moves by local governments to prohibit diesel vehicles, the VDA says "scientific studies" show this move will reduce air pollution just as much as localised traffic bans.

The VDA also welcomed a commitment by the German states and federal government "to prioritise the avoidance of general driving bans".

Just as importantly, the VDA hopes this agreement is the first step in rebuilding the German public's confidence in their nation's auto industry, which has been rocked by the Dieselgate emissions cheating scheme at Volkswagen and on-going investigations elsewhere.

As the association points out, the industry employs 817,000 people in Germany alone. The country's automakers cranked out 15.8 million cars last year, with 5.7 million of those produced on home soil.

Australia

We've reached out to the Australian representatives of the Volkswagen Group, Daimler, BMW and GM about whether these upgrades will filter through to local vehicles.