The third directive, 2004/26/EC, covers diesel fuelled engines from 19 kW to 560kW for common NRMM and regulates the emission in 3 further stages. The directive includes also railcars and locomotives and inland waterway vessels and for the 2 latter categories there are no upper limits concerning engine power. The different stages in the 2004/26/EC directive are as follows:
- Stage III A covers engines from 19 to 560 kW including constant speed engines, railcars, locomotives and inland waterway vessels.
- Stage III B covers engines from 37 to 560 kW including, railcars and locomotives.
- Stage IV covers engines between 56 and 560 kW.
The stage III A will be effective (place on the market) from 1 January 2006 for certain types of engines, stage III B from 1 January 2011 and stage IV from 1 January 2014. In the directive there is a flexibility scheme that allows manufacturers to place engines on the market that only fulfil the previous stage when a new stage is in force.

The directive 2004/26/EC is aligned with the US proposal TIER IV of further stages of emission limit values. A working group within the GRPE - Working Party on Pollution and Energy (UNECE) is working with a world wide harmonised test procedure.

The fourth directive, 2006/105/EC, introduced some modifications to the Directive 97/68/EC, amending Annex VIII, point 1, section 1. This concerns the approval certificate numbering system, with the code for each MS.