Mercedes W219 CLS 320 CDi Throttle Body Fault

Hi guys.

I have this W219 CLS, with a permanent 2376-001 fault (Throttle body output voltage too low).

The car goes in limp mode after starting. Fault cannot be cleared.
The car was already in several workshops which has tried to rectify the problem but without luck.
With the car there are 2 Engine ECU's, original one, and replacement one.
Both have been already opened form the other workshops, the signs for that are clear.

With both ECU the fault is permanent.

Until now I have checked:
- Throttle body, I have a brand new one, and I have just connected it for test, fault still there.
- Wiring from TB to ECU, checked and load tested, no problems.
- Fuse in SAM-F which is responsible for the power supply, checked, good.
- Inlet port shut off motor, I have just disconnected it, in order to test if it has internal short and causes voltage drop, no effect, fault still there.

Basically there is no output voltage from engine ECU to Throttle body pins 1 and 4.
All other actuators which share the same power supply line are OK and working.

Any advices and ideas are welcome.

BR