Genuine OEM Audi Engine Control Unit, part number 4E0990990. This unit is the central computer for the diesel engine, managing critical functions such as fuel injection, ignition timing, and emissions control. It is typically mounted within the engine bay or under the dashboard. The ECU weighs 0.748kg and has dimensions of 0.185m x 0.17m x 0.04m. Genuine OEM ECUs are essential for correct engine performance, fuel efficiency, and emissions compliance due to their precise calibration and integrated firmware.