Audi a3 emission control system light stays

[Tono]

Hi, Recently I purchased an Audi A3 ( 2015, 1.6 TDI 110 SE 8v, automatic) and I noticed that the emission control system light (ECU) appears after the ignition and does not disappear (as the other control lights), just after I start the engine. I am not sure that this is ok or not, so while the engine is running I can't see any warning sign, so hopefully, everything is ok. Do I have to do something about it or is it normal?