Level Sensors: Notes
There are two level sensors in the passive reservoir. One supplies the "Full" signal and the other the "Empty" signal.
The sensors make use of the conductivity of the urea-water solution. When these contacts are wetted with urea-water solution the circuit is closed and current can flow, thus enabling a sensor signal.
The two level sensors send their signal to an evaluator. This evaluator filters the signals and recognizes, for example, sloshing of the urea-water solution and transfers a corresponding level signal to the digital diesel electronics.
The "Full" level sensor is located at the top of the passive reservoir. Both contacts are wetted when the passive reservoir is completely filled and the sensor sends the "Full" signal.
The "Empty" level sensor is located at the bottom end of the passive reservoir. The reservoir is considered to be "not empty" for as long as the sensor is covered by urea-water solution. The evaluator detects that the passive reservoir is empty when no sensor signal is received.