Audi A4 Avant 1.9 TDI: Strange CAN-bus problem

Hello,

Problem: CAN-bus goes crazy Audi A4 Avant TDI Multitronic 2003

As soon as i use the trailer connection on the car (factory placed by Audi)
there are strange things going on.
Sometimes the CAN bus controller for the trailer is not driving the lights, but the computer is not giving a feedback as broken bulb.
On other moments all seems to work normaly but when used on a hot day I start to have other problems:
-After disconnecting the trailer the trailer indication keeps functioning
-The Radio-GPS combination must be turned on manualy after the cas is parked for +/-3 Hr
-The CAN system keeps burning electricity, therby draining the battery
Once the CAN system is reset after a completely drained battery the draining stops. (happend twice last year )

Last year they already changed in the garage the CAN controller for the trailer, the radio AND the main CAN controller (in the dashboard)
Then everything seemed ok

Last WE i used the trailer connection again, it was hot (airco working)
Result: All problems are again present like last year. And the battery is getting draind again like last year.

Is there anybody out there who can help?