The probe has four wires: two for power and ground, and two for the sensor signal.
The sensor works by using a float switch or a reed switch. The float switch is a simple switch that opens and closes when the coolant level rises and falls. The reed switch is a magnetic switch that is activated by a magnet attached to the float.
When the coolant level is high enough, the float or magnet activates the switch, which sends a signal to the vehicle's computer. The computer then knows that the coolant level is normal and does not take any action.
4-wire coolant level probes are more complex than 2-wire probes, but they offer a number of advantages. First, they are more accurate and reliable. Second, they can provide more information to the vehicle's computer, such as the exact level of coolant in the reservoir tank.
