W168 Long 2004 - FTC ECU Problem - CAN BUS Comm.

Hello Everyone,
I've been using this car for over than 2 years.
There was a similar fault when I first bought it, but when I changed the ftc ecu, the problem was gone.
I've been having the same problem for about 2 months and this time it doesn't get better even though I changed it with the new one.
When we connect the vehicle to the machine, we do not see the FTC ECU and therefore we cannot get an error code.
It only gives CAM BUS communication error.
The master says he checked all the electrical cables that might be related to the glass, but the problem still persists. When we turn the key, the 1-second P signal comes and goes. It does the same with D or R, but it just disappears.
Does anyone know that is there any specific reason causes this problem ?
Thank you in advance for your replies, i really appreciate that.
Best,
Murat