In January 1996 Mercedes-Benz has introduced a new 4-cylinder engine OM 904 LA of the new engine family for light commercial vehicles. The power range of the OM 904 LA comprises ratings from 90 kW up to 125 kW at 2300 rpm.From the beginning of the design of this engine, a noise emission output as low as possible was strived for, aside from the high targets as far as durability, maintenace and fuel consumption are concerned. The basis is the development of noise regulations for commercial vehicles.The noise reduction measures have to be concentrated on the engine since up to now it still is one of the main noise emission sources at the vehicle. Already at the lay-out of the engine the prerequisits for a low-noise engine behaviour have been taken into consideration. The engine is equipped with a fuel injection system featuring particular unit injector pumps for each cylinder which is superior to the conventional in-line injection pump as far as acoustics are concerned. In addition, the valve gear train has been positioned from the front to the fly-wheel side of the engine. In the further stage of development improvements of the structural dynamics have been obtained by application of FE calculations.By a large variety of noise and vibration measurements the main noise sources have been detected.Further on, optimization of engine components, partially supported by experimental modal analysis, has been acomplished.In this paper, the different partial noise sources with their respective problems are to be described, and the effectiveness of the acoustical measures taken are to be shown.