Golf 3 Variant (1Z) Diagnostic socket defective, located on the vehicle side.

Hello,

In addition to the other problem with starting difficulties, it is further complicated by the fact that I am unable to access the control units, as the diagnostic port on the car is malfunctioning ("no control units found").
Everything is fine with the gasoline engine (also G3).
At the lower right pin, I have been able to identify the power supply.
Does anyone have any ideas or "experience-based" information on where such errors are most commonly found/to be fixed (cable breaks, switchboard installation, etc.)?

Thank you,
Hi