Oil Condition Sensor

Oil Condition Sensor

Oil condition sensor
The oil condition sensor increases the function range of the thermal oil level sensor. The oil condition sensor measures the following variables:
- Engine oil temperature
- Oil level
- Dielectric conductivity

The engine control system evaluates these measurements. With the oil condition sensor, the electrical properties of the engine oil are also determined. The properties change as a result of engine wear as well as in the engine's oil (such as ageing, entries).

Functional description
The oil condition sensor is attached to the oil sump and is accessible from below. The oil dipstick has been deleted from all of the new engine series (except diesel engines). Electronic oil-level monitoring is now a feature of all engines.
The oil condition sensor consists of 2 cylindrical condensers. The condensers are mounted above one another. 2 metal tubes are inserted one into the other to serve as electrodes. The engine oil is used as a dielectric medium between the electrodes.







NOTICE: Explanation of the terms 'dielectric' and 'permittivity'.

A dielectric is defined as a non-conductive material in an electrical field. An insulator penetrates the electrical field.
Permittivity (lat.: permittere = permit, let through) is also referred to as the dielectric conductance. The permittivity specifies the degree to which materials allow electrical fields to pass. The factor indicates by how much the voltage at a capacitor drops when a dielectric, non-conducting material is arranged between the capacitor plates. The temperature sensor is seated on the housing of the oil condition sensor. The housing of the oil condition sensor contains an electronic evaluation unit. The electronic evaluation unit has self-diagnosis. A fault in the oil condition sensor is entered in the fault memory of the engine control system.
The electrical material properties of the engine oil change as the engine oil wears and ages. The changed electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor to change.
The electronic evaluation unit converts the measured capacity into a digital signal. The digital sensor signal is sent to the engine control system. The engine control system uses the signal for internal calculations (e.g. condensate in the engine oil).
The oil level is measured for the electronic oil level check. The 2nd capacitor in the upper part of the oil condition sensor registers the oil level with the engine running. The capacitor is at the same level as the oil level in the oil sump. As the oil level changes, the capacitance of the capacitor changes. The electronic evaluation unit creates a digital signal from this. The engine-management system employs this as the basis for calculating the engine's oil level. The electronic oil level check is displayed on the Central Information Display (CID) as well as in the instrument panel. On vehicles without a CID Central Information Display the oil level is only shown in the instrument cluster.

Structure and inner electrical connection
The oil condition sensor is connected via a bit-serial data interface to the engine control system. Power is supplied via terminal 87.
The electronic monitoring circuitry is completely contained within the electronic component and employs capacitance measurement to operate.







Measurement procedure and target values







Please note the following specifications for the oil-level sensor:

Size Value
Voltage range 9 to 16 V
Oil level measurement range 0 to 75 mm
Permittivity measurement range 1 to 6
Maximum conductivity in oil 0.02 mS
Temperature range -40 to 160 deg C

Diagnosis instructions

Failure of the component
The following symptoms may be expected in the event of a failure in the oil-condition sensor:
- Fault entry in the engine control unit
- The engine control unit calculates substitute data for the engine oil service

General notes

NOTICE: Condensation in the engine oil.

Condensate that forms in the crankcase due to short distance driving can influence the permittivity. As water enters the engine oil and mixes with it, moisture also collects around the oil level sensor. When excessive moisture or water is present within the crankcase: Individual instances of incorrect oil level displays may occur, while a spurious warning indicating that the oil should be topped up is also possible. The diagnostic system can process this "spurious oil-level warning" with fault pattern selection in an operation that also assesses the permittivity of the oil. However, there is no direct display of the permittivity. Among the factors that affect the oil's permittivity are its viscosity and its age. This means that an accurate assessment of oil quality cannot be guaranteed under all conditions.

We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.