Audi Repair Questions? Ask a Mechanic for Answers ASAP
U codes are communication errors. You have either got a fault with the CAN or LIN Bus System or a fault with the Control Module.
The first port of call with this woul dbe a full Diagnostic Code Read followed by a CAN Bus Diagnostic which should show up any faults with the CAN lines.
Following this it will be a case of Continuity Check on whichever CAN Lines are showing as not working, If the Continuity Check of the CAN Lines are ok then it points to the Control Module.
For further information on CAN Diagnosis you can look at the Diagnostic Information on ErWin which will also show you teh Wiring Diagrams. This is available here: Audi ErWin