Engine Oil Pressure Switch (Built Before 06-16-2014)
WARNING: This page is about a different car, the 2015 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
Without oil pressure, the engine oil pressure switch is a normally open switch. The PCM provides a reference voltage to the engine oil pressure switch when the ignition is in RUN. With the engine running and low or no oil pressure, the engine oil pressure switch remains open. The PCM detects no change in the reference voltage and provides a request to the IPC to illuminate the low oil pressure warning indicator. With the engine running and sufficient oil pressure, the engine oil pressure switch closes, pulling the reference voltage low. The PCM detects the low reference voltage and provides a request to the IPC to turn off the low oil pressure warning indicator.