Oil Level Sensor: Description and Operation

Basic System Description:

Signal Assignment Oil Sensor B40:

Task
- warning the driver that the oil level is too low by means of an indication in the instrument cluster
- Detecting oil temperature
- Detecting oil quality for need-based oil change interval display

Design/function
Oil level, oil temperature and oil quality are detected by means of an oil sensor integrated in the oil pan. The sensor which operates on the capacitance principle features an integrated electronic circuit which analyzes the three signals.

The information is constantly transmitted as a PWM signal to the engine control module and over the CAN to the instrument cluster. Each information block consists of three successive square- wave signals, followed by a short pause. This is followed by a short pause. A measured variable is assigned to each square wave signal (A, B, C). The relative quantification is carried Out on the basis of the on/off ratio of approx. 19 - 81 %.

The oil quality is detected for indicating the need-based oil change interval. The oil quality is detected on the basis of the capacitance of the engine oil (dielectric), this being as much as 6 times greater if the oil quality is poor.

The measuring range for the oil level is 80 mm (normal level ± 40 mm), the measuring accuracy being approx. ± 3 mm.

Oil level and oil quality (capacitance of the engine oil) are independent of each other. The information is first of all compensated in the engine control module before being transmitted over the CAN.

Faults at the oil sensor are detected by the engine control module and entered in the fault memory.

The voltage for the oil sensor (approx. 5 V) is supplied by the engine control module.

Instrument cluster
- CAN-compatible

CAN data bus, function
- Networking of engine CAN bus