Engine oil monitoring, function

General

The oil sensor constantly monitors the oil level and relays the relevant data to the ASSYST processor.

Oil top-ups are detected automatically and provide a bonus which extends the service interval accordingly.

An incorrect oil level at maximum is displayed:

 On demand from the driver

Warnings are displayed:

 Automatically, no earlier than 60 seconds after engine start and with oil temperature greater than 60°C:

 If the oil level is too high, the oil level warning lamp lights up and the display "HI" flashes; a short warning tone is also sounded

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 If the oil level is too low, the oil level warning lamp (A1e12) lights up and the display "-1.5 L" flashes; a short warning tone is also sounded

 At the minimum oil level the oil level warning lamp (A1e12) lights up; a short warning tone is also sounded

 Automatically 13 seconds after ignition ON:
 If there is no oil in the engine, the oil level warning lamp (A1e12) lights up and the display "-1.5 L" flashes; a short warning tone is also sounded.

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The incorrect oil level displayed is not changed while the display is on. In other words, any change in the oil level is not immediately observable on the display. The new oil level is only displayed according to the conditions described below.

Displaying oil level on demand

Ten seconds after the starter switch is turned to position "2" the oil can and clock symbols appear on the display.

If the reset button for the trip odometer is pressed twice within one second while this display is showing, a message appears on the display, e.g. "-1.0L" if the oil level is low. The display appears only when a certain waiting time has elapsed after engine OFF. The waiting time depends on the engine oil temperature, and lasts

 up to 20°C 30 minutes

 above 60°C 1 minute

 At other temperatures the waiting time adopts corresponding intermediate values.

Possible displays are as follows:

 "o.k."

 -1.0L, -1.5L

 "HI"

 Clock symbol flashing and oil can symbol

 Clock and oil can symbol

In the event of a fault in the oil sensor (oil level/temperature/quality, B40) the oil level warning lamp (A1e12) lights up.

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For diagnosis purposes the ECM or CR control module can be interrogated using Star Diagnosis.

Oil change

ASSYST must be reset after every oil change. The remaining mileage and the remaining time are reset. The system can be reset either via the instrument cluster or by means of Star Diagnosis.

The following data is stored when the system is reset:

 Current mileage rounded to the nearest 100

 Total top-up quantities in the last service interval

 Remaining mileage

 Remaining time

 Product of quality factors

 Data of the last five resets

This data can only be retrieved using Star Diagnosis!

If the specified oil quantity was not added at the last oil change, the (internal) startup mileage is reduced.

Top-up detection

Star Diagnosis can be used to call up the last ten top-up quantities and the corresponding mileage readings from the current service interval.

Normally, the detection of an oil top-up is indicated by an increased remaining mileage reading in the instrument cluster.

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Oil top-ups are only detected when the following conditions are satisfied:

 The top-up quantity amounts to at least 1 liter

 After the top-up a distance of at least five kilometers must be drive under normal driving conditions with an oil temperature of at least 60 °C.

There are cases, however, where the remaining mileage display still appears to be implausible after a top-up; according to the display only a very small bonus or none at all is gained. This is because the remaining mileage is only ever shown in the range from 15 000 km to 30 000 km (or 20 000 km to 40 000 km for engine 668), but is calculated internally using the actual values, which may also lie outside this range. These internal values can only be retrieved using Star Diagnosis.

The graphs below illustrate a few

examples. The horizontal (X-)axis represents the service interval and the vertical (Y-)axis the remaining mileage in kilometers.

The ASSYST display in the instrument cluster always moves in the light unshaded area.

The internally calculated remaining mileage, however, may stray inside the two shaded areas. These internal values can only be retrieved using Star Diagnosis.

All the examples below refer to gasoline engines.

P00.20-0201-06

Example 1:

Enough oil was added at the last oil change so that the startup mileage is 15 000 km.

After 10 000 km the oil is topped up under normal driving conditions (a). The bonus (B1) is awarded and displayed. When the remaining mileage is called up, a higher remaining mileage figure is displayed.

After another 5 000 km (b) the oil is topped up again. Here too a bonus (B2) is awarded and displayed. If the vehicle continues to be driven with the same driving style and no more oil is added, a service interval of approx. 24 000 km can be achieved.

In this example the curve remains within the unshaded area of the graph at all times. For this reason all oil top-ups are indicated with an increased remaining mileage reading.

P00.20-0204-06

Example 2:

The specified oil quantity was added at the last oil change.

Under extremely favorable driving conditions the oil is topped up after
10 000 km (a). Internally the bonus B1 is awarded and the service interval is extended accordingly with a higher remaining mileage. However, since the curve is partially inside the shaded area, initially only that part of B1 which is inside the unshaded area is displayed as an extension of the remaining mileage.

At 18 000 km the oil is topped up again (b). Because the maximum service interval of
30 000 km is exceeded, no extension is indicated at first for the bonus B2. The total service interval in this case amounts to
30 000 km.

If the vehicle is driven under less favorable conditions after point b, the maximum service interval of 30 000 km may be achieved on account of the internal
bonus B2.

P00.20-0202-06

Example 3:

Less than the specified oil quantity was added at the last oil change. The startup mileage is therefore less than 15 000 km.

If the oil is then topped up after 5 000 km (a), the displayed remaining mileage is not extended because the curve is now entirely inside the shaded area. However, the bonus B1 is credited internally and results in an extension of the service interval to slightly more than 15 000 km under the same or better driving conditions.

The service interval of 15 000 km is always achieved, even if the internal value were lower.

P00.20-0203-06

Example 4:

After 5 000 km under unfavorable driving conditions, the oil was topped up (a) and the top-up (bonus B1) was registered internally.

Now two possible cases are considered:

 If the vehicle continues to be driven under the same conditions (unbroken line), the displayed remaining mileage is not extended because the curve is inside the shaded area.
The service interval is still 15 000 km, even though the internal value is less.

The displayed remaining mileage can only ever move inside the unshaded area.

 If the vehicle is driven under more favorable conditions (dotted line), the internal remaining mileage value gradually moves back into the unshaded area. The service interval can therefore become more than
15 000 km.