Oil Condition

Oil Condition

An oil condition sensor records the exact engine oil level, oil temperature and the condition of the engine oil. Recording the engine oil level protects the engine from having a level which is too low which will result in engine damage. Recording the condition of the oil means that it is possible to determine exactly when an oil change is required.

Oil Condition Sensor (OZS): The electronic condition sensor is located in the engine sump mounted to the engine oil pan.




The sensor consists of two connected cylinder capacitors. The smaller capacitor (6) records the oil condition. Two metal tubes (2+3) act as capacitor electrodes located inside the sensor. The engine oil (4) dielectric is located between the electrodes.

With increased wear and additive deterioration, the electrical material properties of the engine oil change.




The different electrical material properties of the engine oil (dielectric) change the capacitance of the oil condition sensor. This capacitance value is processed to a digital square wave signal in the evaluation electronics (7) which is integrated in the sensor. This signal is sent to the ECM over the BSD interface as a "statement" about the engine oil condition. The ECM processes this sensor value to calculate the next oil change service.

The engine oil level is determined in the upper section of the sensor (5). This part of the sensor is located on the top of the oil level in the oil sump. As the oil level lowers (dielectric), the capacitance of the sensor also changes. The sensor electronics process this capacitance value into a digital square wave signal which is also sent over the BSD interface to the ECM.

A platinum temperature sensor (9) is integrated at the base of the oil condition sensor to measure the oil temperature. The engine oil level, oil temperature and engine oil condition are constantly recorded when voltage is supplied (KL15). The oil condition sensor is supplied with voltage from the IVM.




The oil condition sensor electronics performs its own diagnostics. A fault in the OEZS results in a corresponding error message that is transmitted over the BSD interface to the ECM for fault storage.