An oil pressure switch, also called an oil pressure sending unit, measures the oil pressure at which your engine is operating. The pressure is converted into an electronic signal, registered on your dashboard on a gauge or warning light. Over time, oil pressure switches can fail and display inaccurate readings or, sometimes, none at all. Replacing the switch is straightforward and accomplished with just a few tools.
Turn the engine off and allow it to cool down. Open the bonnet and locate the oil pressure switch. The location of the switch is different for every vehicle, however, it is usually located along one side of the engine block. Clean around the switch with a shop rag to remove oil and grit.
Disconnect the wiring harness plug from the oil pressure switch.
The oil pressure switch is screwed into the engine block. Turn the oil pressure switch counterclockwise with a wrench, then unscrew it all the way to remove it.
The new pressure switch may have thread sealant on its threads. If it does not, apply some automotive thread sealant to the threads, then screw it into the threaded hole in the engine block. Tighten the switch according to the manufacturer's specifications. The threads are NPT (National Pipe Thread) standard and are tapered, so it is easy to over-tighten if you are not careful.
Connect the wiring harness plug into the new switch. Make sure the plug seats all the way and clicks into position.
Check for leaks once you start the engine to insure that no oil is seeping past the new switch's threads.
Do not use Teflon tape as thread sealant. Teflon tape is designed for use with water connections. Oil will degrade the tape and seep past the threads over time.