Grades in Europe are visia, acenta, acenta+, and tekna. I have acenta grade with keyless and auto pack. In my CAN harness are 4 can wires conected to radio - 2 communication H & L and two termination H & L, dont know what does it mean), by data line connector it goes to/from combination metter, steering wheel angle sensor and BCM and other devices. And there is also 2nd degree CAN loop/circuit which starts from BCM and ends in BCM. With this second loop i found that BCM works as CAN gateway. In my car It connects Auto HVAC controller and distance sensor. In tekna grade with avm & navi it's additionally split for avm and navi. So my BCM in this 2nd CAN line connects two devices (HVAC controller, distance sensor). In tekna four (HVAC, distance sensor, navi, avm). Till now i tested navi in car with 4 CAN wires connected, speakers, ignition, baterry and ground. I didn't connect speed, illumination, dimmer, reverse signal, mic, aux and usb. I didn't connect too AV CAN H & L in this second loop/ circuit affraid of locking navi to red. I heard that in Europe it checks immo and vin and if data doesn't match it block navi permanently. Don't know what is difference between secure lock green and red level. In home I connected AVM and Navi with AV-CAN-H & L, and camera image signal, and shield. Also connected to both battery voltage, ignition, ground and reverse. Navi works in car and in home. As i wrote speakers are ok, navigation with connected gps ant. works, phone by bluetooth works - i have additional mic same as in car. I didnt check usb and aux. AVM feeds camera with 6V - i connected in home front camera - 6V, cam signal, ground and shield with avm according to wiring diagram. Try to pop out camera image by put reverse signal to avm and navi, tried by push camera button. Nothing happened. I wonder maybe it works when not only avm is connected to navi but also with BCM, and additionally speed signal, steering angle...
In workshop manual in section troubleshots there is dtc U1000 "Control Unit (CAN)"->the Around view monitor system does not operate"
Maybe without connection with BCM (as CAN gateway) it won't work when only navi and avm are tied.
I forgot, i have not TCM. I have manual transmission. It takes signal from sensor under car, gives it to ipdm, and ipdm route it to reverse/back lamps and to navi and avm.