BMW Engine Oil Pressure Switch - Hella 003259121

Product Information

The engine oil pressure switch detects oil pressure and sends a signal to the ECU, most specifically for use in the dashboard warning light (“genie lamp”). This ensures that if there is a sudden loss of oil pressure, then the driver is warned and can safely come to a stop. Without oil pressure, the engine can catastrophically fail, so if you are diagnosing a suspected oil pressure problem, the oil pressure switch should be inspected. Oil pressure switches differ from oil pressure sensors which output a range, rather than just on or off. Modern cars may use a sensor instead of a switch to get additional oil pressure data for the ECU to use.

The switch itself is usually a small threaded metal body that screws into an oil passageway in the block, head, or occasionally the oil filter housing. A very small hole on the end allows ingress of engine oil, and inside the switch, there is a diaphragm and an electrical component. When oil pressure is pressed on the diaphragm, contact is made, and the electrical circuit is completed.

Engine oil pressure switches are very simple, so when they fail the issue generally isn’t with the pressure sensing mechanism itself. Rather, faults with this switch are more common with the electrical connector and its terminals, as well as oil leaks. If your oil light stays on when starting the engine, and nothing else has changed, inspect the wiring to the sensor before assuming the worst. Engine oil pressure switches are usually designed to be installed with the socket going over the electrical connector, so keep in mind the size socket you may need when replacing your oil pressure switch.

• Electrical connector failure: The engine oil pressure switch is subjected to high heat and chemical conditions, which can degrade the plastic and wear the terminals. If the electrical connector is broken or loose, the oil warning light may not extinguish.
• Internal failure: While not as common, if the internal diagram is sticky or may have been out of a car for a long period as a used part, the reading might be sluggish or stuck.
• External oil leaks: It is very common for an oil pressure sensor to leak oil after many years and miles. Sometimes the oil sealing ring is captured on the threads so if an external oil leak occurs the whole switch should be replaced.
• Internal oil leaks: It’s possible for an internal oil leak to make it past the electrical seals and into the electrical connector. It’s important to catch a failure like this early, to avoid oil from wicking up into the vehicle harness.

About Hella

Hella is a German based manufacturer of specialty lighting parts for automobiles and is an OEM (Original Equipment Manufacturer) for Audi, BMW, Mercedes, Mini, Subaru , Toyota, Volkswagen and more. Hella lighting solutions include headlights and fog-lights, complete headlight assemblies, and all the other internal bells and whistles that allow your vehicles lighting system to run impeccably every time you turn the ignition over. One of the most well-known automotive suppliers, Hella ranks highly among the top 50 producers of parts in the entire world and has expanded beyond lighting and into electronics for vehicle interiors. The company was technically founded in 1899, and initially was a producer of candles and lamps for horse drawn carriages. A lot has changed in over 100 years.