Audi Repair: Audi A4 1.9TDI fault code P1850, speed gearbox, esp light

Question
I have a 2004 audi A4 2004 B6 1.9TDI Sport, manual 6 speed gearbox, which intermittently stops running or won't start. After around three minutes it will re-start and runs 100% ok. If the car is running, the ESP light flashes several times and then comes on, and cannot be reset (switched back on) until the car will re-start. This only occasionally happens, but the frequency is increasing. I have had a diagnostic run by my local independent VAG garage, which has given a 18258 P1850 035 fault code, "data bus drive info missing from engine CU sporadic fault". The garage could not offer to fix this, and suggested I would have to go to a Audi dealer. This will be a very expensive repair. Can you suggest where the problem lies, and the remedies I should try without having to have a new mortgage. I am capable of some car DIY work.
Help would be greatly appreciated.

Answer
Even though this is a diesel engine, modern diesels do rely on some electrical systems, and it sounds like a connection or a relay is giving a poor contact.  Is the problem worse when the engine is cold, try and find some correlation with temperature or other conditions whihc may help trace the problem.  The fault you describe is likely to be just a connection, sensor or relay, but some garages will jump right in and try to replace the computer, which is hardly ever the problem, but very expensive to the customer.  At this point I would check the connections to the engine control computer, and check connectiosn to the sensors specifically in the engine bay area.  Let me know if you find anything,  Jan