Oil pressure in an engine is critical to proper operation and to avoiding irreparable damage to internal engine parts. Electric oil pressure gauges sense the oil pressure inside the engine, then transmit the pressure information to the gauge inside the vehicle. A malfunctioning oil pressure sensor may send erroneous information to the gauge. Test the sensor before you replace the gauge. The sensor screws into the engine block, which connects to the gauge by a wire that is routed through the firewall to the gauge on the dashboard.
Find the oil pressure specification for your model vehicle and engine size in your owner's manual or a vehicle service manual for your car. Find the voltage and resistance parameters for the oil pressure sensing unit in your vehicle's service manual.
Disconnect the wires that attach to the oil pressure sensing unit. It's usually located on the bottom of the engine near the oil filter. Attach the multimeter that leads to the sensor and then start the vehicle. Check the multimeter and note the voltage and resistance reported by the multimeter.
Turn off the vehicle and disconnect the multimeter. Connect the potentiometer to the oil pressure sensing unit by connecting one lead to the blue and white wire on the sensor and the other potentiometer connection to the ground connection on the frame.
Set the potentiometer to the resistance (in ohms) as specified by your owner's or service manual. Start the vehicle. Check the reading on the potentiometer and note the resistance. Turn off the vehicle, disconnect the potentiometer and reconnect the leads to the oil pressure sensor.
Replace an oil pressure sending unit that returns values outside the acceptable range for your model vehicle. Replace the electronic oil pressure gauge if the sending unit tested within acceptable ranges.
Check the oil level in your vehicle before testing gauges and sensors. Oil pressure is affected by improper oil levels. Sometimes cleaning the dirt and grime build-up off the sensor will resolve the problem of an incorrect gauge reading.
Do not attempt to replace a faulty sensor or gauge if your vehicle is still under warranty. Take it to an authorised dealer. Do not attempt to replace an oil sensor or a gauge if you are not sure how to complete the job.