Peugeot 807 Parking Assist Error: No Power to Sensors, Troubleshooting & Diagbox Results

Hello to all forum members.
I searched but found no answer.
So I will describe my problem with the recently purchased Peugeot 807.
I have a problem with the parking assist error message. It is displayed immediately after starting the car, and the triangle symbol on the board and another message and sound signal after throwing the car backwards (automatic).
After diagboxing, I know that I am catching the error "no power to parking sensors". Of course, I checked the fuses in all 3 places first.
There are 2 dice in the module, black and blue. Black 4 wires, blue 6. My questions:
1. On which of the pins / wires should the voltage supplying the sensors appear after throwing R?
2. The reverse lights work without any problems, although after the measurements I did not find any wire entering the module on which the current would appear after throwing backwards. Is the triggering of the sensors can be controlled or just 12V from the lamp / beam?
One of the wires in the black bone is 12 V before turning on the ignition, after starting the car, the voltage drops to 4.5 V and the voltage appears on the other of the 4 wires. There are two blue wires. The other two, that is, red and probably white, are solid masses. I thought that the red voltage should appear after throwing in the reverse, but it is ground (unless it is a short to ground error, this wire).
I have no way to get under the car, so I cannot check the status of sensors, harness. No buzzer feedback whatsoever and no distance display on the lcd and I got it running. I was checking lexia,
none of the sensors are ticking or whistling etc. Thanks for the suggestions.

Year of production?
Until 2006, MUX was promoted - CAN-VAN.
From 2006 there is only CAN.

Sorry for the lack of details. 2007. Today I measured everything again. On the inserted blue cube (I suspect this one is appropriate for the sensor-module bundle) and I have such observations. There are 6 cables. According to what I read, it is a plus, mass, and signals from 4 sensors. For me it is: One constant plus. On 3 after throwing the reverse on the engine, 11.8v. On a permanent plus after firing, it increases from 12.6 to 13.9-14.1, which is normal. On two kaabelkach, ie. Purple and yellow, I have a constant weight. I suspect that one of them should also be 11.8 but due to the released sensor there is a short to ground. Is my reasoning logical?
If so, I go under the car and look for a sensor with a yellow or purple cable. I would like to add that diagbox crashes the sensor power supply error, not the specific sensor. Could a short circuit of one sensor to ground cause the entire system to disconnect, or would just that one sensor fail? After removing the yellow and purple pins for the test, no improvement. Perhaps the entire system with one sensor unfastened will not start either.

Hello. Problem solved. One of the sensors turned out to be the culprit, it had a short to ground. Interestingly, lexia indicated which sensor it was after a few readings. After replacement, everything works as it should. I close the topic