Coolant level probe
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Monitoring the coolant level
All engines are equipped with either one or two coolant level probes for monitoring the coolant level in the
coolant expansion tank. This probe is of the capacitative type. The sensor and the evaluating electronics
form a unit.
If the coolant falls below the level monitored a minus potential is sent to the signal output ”S”. With this a
check lamp or a relay can be triggered.
Checking the coolant level probe
The probe features an integrated checking function. As soon as voltage is applied to the probe the signal
appears for approx. 2 seconds to signalise that the probe is ready for operation.
If this signal does not appear, the probe must be checked.
It is not possible to carry out a functional check by measuring the resistance (ohmmeter) because of the
internal transistors.
The check can be carried out with a water tank and a small test bulb (< 3 watt).
Dip the probe into the water and apply a supply voltage of 24 V to the plus and minus leads. The output ”S”
is to be connected to the plus lead via the test lamp. The test lamp does not come on.
If the probe is taken out of the water, the test lamp must come on after approx. 7 seconds.
If the lamp does not come on the probe is defective and must be changed.
24V
+
–
S
max. 3 W
+
–
S
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