The black wire is a trigger output which activates when the system detects an object. For example, to activate a warning alarm. The output is a switched ground with a limit of 250mA and must be connected via a diode protected relay to prevent irreversible damage to the system.
The first thing to do is to cover the face of the sensor with light pressure (using a finger or thumb) if the detection stops it implies the sensor is detecting an object.
It is always best practice to mount sensors where they will not detect parts of the vehicle but if this is unavoidable then the system has a feature called Environmental learning mode (ELM). ELM can be used to ignore limited objects that do not move relative to the sensors.
To activate ELM the system power needs to be turned on/off/on 4 times, please allow the system to power up and detect before switching the power back off each time (about 6 seconds between cycles). When the system is switched back on for the 5th time it should not detect the object.
Please be sure to test the detection performance of the system after applying ELM.
All UDS systems have a self-diagnostic feature that checks for faulty sensors when the system powers up. The system will give a single beep for each sensor that is not working. So, one beep identifies one faulty sensor, two beeps identify two faulty sensors, etc…