Reacononly

Hi. Not sure if anyone could help me in this but ill try anyways. I have a 2000 A3 1.9Tdi AHF, the car works, but everytime i try to read the fault codes it just shows that theres no connection to the ecu. And even if i get it to connect, theres always an intermittent fault code "Lost connection to the ECU". I was wondering maybe someone has had the same problem and should i be concerned.
The car works great, it shows things like low brake fluid etc. The ECU also is working, i can connect to other modules like Airbags or the dashboard itself, its the main engine control module that wont connect. I have tried multiple diagnostic tools too.