Engine pressure sensors constantly test oil pressure through the use of an oil pressure sending unit inside the vehicle's block or cast area, according to YouFixCars.com. Most vehicles include a factory-installed fuel pressure sensor that can be removed in order to test the car's oil pressure.
When testing engine oil pressure by removing the factory-installed sensor, follow the instructions provided with the fluid pressure tester. Some testers are designed to test pressure for both transmission and engine oil. For better results, use compound or Teflon tape on each of the connection fittings to ensure a stable contact.
Look up the specifications of the particular engine being tested in the relevant car repair manual to help ensure accurate results. Take a reading of the oil pressure at normal operating temperature, and record the results at idle speed, which is generally around 2,000 rpm.
Low oil pressure results may be caused by excessive bearing clearances, restricted pump pickup screens, a weak or broken pressure relief valve, or a low oil level. In some cases, the contamination of oil by foreign particles can create conditions that lead to low oil pressure. Using a low viscosity oil may also produce low oil pressure readings.