If a sensor is defective, the D4P control unit emit a series of flashes of the LEDs in RED and GREEN incorporated, the control unit indicates the number of faulty sensor. Note that if you have left off all sensors, each LED will blink four times, indicating that the high level sensor is detected. If you change the sensor and the error persists, sure the problem is the cable or which are not seen are rear sensors, check that they are not active.
In addition if you connect a LED display to the area with fault sensor, the LED display will show for 2 seconds the total number of faulty sensors (E4 = all sensors) and the location of the fault (red LED of display)
It is very difficult for a factory sensor is faulty. The sensors are checked one by one in manufacturing and also after a test one by one before going to market.
Posted in: 2. End user tech support and troubleshooting