In cars with an internal combustion engine, a fluid pressure sensor is used to control the pressure of the motor oil. In most modern vehicles, this is a pressure relay. However, old vehicles and some modern high -class cars use monitoring products and display of actual oil pressure. The liquid pressure relay simply controls the presence or absence of a liquid in the immediate vicinity of the sensor. Oil pressure sensors detect fluid pressure in many respects in the same way as air pressure sensors, as a rule, using a diaphragm that moves or bends with high pressure.