This looks like a high speed CAN fault, the Diag socket reads from the CIM unit, which is connected in turn with the twisted pair of CAN wires to the YRS if fitted then ABS,EHPS,AHL,TCM and finaly the ECM, both the CIM and the ECM have 120 Ohm resistors in them accross the CAN lines to give you the 60 Ohms line resistance, if the line resistance is good it is possible you have a CIM unit fault, I have changed a number of them to date its seems to be a common fault with the VECTRA C,