Readout problems via ODB?

Connecting the ODB readout only reads certain information from the ECU. Do not get full access to the ECU. Therefore, warning and fault codes can't be read. The engine runs perfectly so it seems that the ECU is working. Had the car also checked at a company that can repair ECU's and they think it is a fault between the cable of the ODB and the ECU. Yellow marked cable in the attached PDF document. How to check this? How to find the right pins on the connectors to measure if the cable is okay? The read-out was carried out by the Skoda garage, and they could not get into the ECU. They recommend a ECU replacement but that will cost 1000 Euro. The car is in Europe and has 270,000 KM. Since the engine has a few error codes but is running with no power-loss I think the ECU is still fine. Or at least a replacement is not the first option. Would need help to get the right cable and disassemble instructions.