2004 BMW 645Ci Engine Oil Level Sensor Replacement Cost

The engine in a car, truck, or SUV contains many metal components that produce friction when they are moving. Oil is used as a lubricant to reduce this friction and to mitigate the heat that is generated in the engine. Over time, the oil will break down, primarily because of the heat. Therefore, oil replacement is an important part of routine vehicle maintenance. When the oil begins to degrade, it loses some of its lubricating and cooling properties. If left for too long, the degraded oil forms a sludge that builds up on engine components and in the bottom of the oil pan. The oil level will also drop. When the oil level decreases, the thermal breakdown (and other forms of oil degradation) is accelerated. This accelerated breakdown of the oil can happen when the engine has an oil leak as well. To alert the driver to a low oil condition in the engine - whether from breakdown or from a leak - an engine oil level sensor located in the oil pan triggers a warning lamp on the dashboard.

An engine oil level sensor uses a float switch inside the oil pan that is normally off when the engine oil level is within an acceptable range. When the level drops, the float drops and the switch turns on, sending a signal to the Powertrain Control Module (PCM) which, in turn, lights up the oil level warning lamp on the dashboard. The PCM monitors the oil level and engine temperature when the engine is in operation.

A bad oil level sensor may cause a false reading of the engine oil level. The oil level warning light may illuminate even when the oil level (checked manually) is within an acceptable range. The warning light may also come on and off intermittently if the sensor is faulty. An error code may be sent to the PCM and a check engine light may come on the dashboard as well if the sensor is bad.