Denso-Common Rail System – Oil level/temperature sensor

1 Oil level/temperature sensor
2 Openings
3 Oil dipstick

The 135 PS version of the 2.4l Duratorq-TDCi in the Transit 2006.5 (at the time of going to press) is equipped with an oil level/temperature sensor.

The quality of the engine oil is calculated using this sensor and a strategy implemented in the PCM. This measure is also able to increase the oil change intervals in this version.

Furthermore, the driver receives an indication via the driver information system when the engine oil level has dropped below the limit.

1 Electrical connector
2 Wire loop
3 Temperature sensor (NTC)
4 Oil level/temperature sensor

The oil level/temperature sensor comprises a wire loop, which is immersed in the engine oil to a greater or lesser extent corresponding to the oil level. At the time of the oil level measurement, a regulator circuit in the PCM closes the circuit of the wire loop. The regulator circuit regulates a constant current flow of 195 mA through the wire loop. The constant current flow heats the wire loop in a specific way.

The voltage drop (U0) across the wire loop is measured immediately after the circuit closes. Another measurement (U1) takes place approximately 1.75 seconds later.

Between the first measurement (U0) and the second measurement (U1) there is a temperature drop at the wire loop. It is dependent on the extent to which the wire loop is immersed in the engine oil.

The temperature drop results from the dissipation of heat from the wire loop to the engine oil. This temperature drop causes a change in resistance of the wire loop and thus also a change in the voltage drop. The voltage drop is used by the PCM as an indicator for calculating the oil level and the oil quality.

The integral temperature sensor measures the current engine oil temperature and is used as a correction factor for the oil level calculation.

Prerequisites for the measurement

Two conditions must be satisfied in order to ensure the measurement is correct:
• The engine must be stopped for a certain period of time (the planned period is up to two minutes – detailed information was not available at the time of going to press). This provides an adequate return flow of engine oil into the oil pan. In this time, the power supply of the PCM is maintained (Power Latch Phase).
• The vehicle must be standing on a horizontal surface. After completing the second measurement, the PCM calculates the oil level. The calculated value is stored.

Strategy for determining a horizontal surface

Vref Reference voltage S Signal to the GEM
1 Instrument cluster
4 Fuel pump and level indicator module

In order to ensure a correct measurement of the oil level, the strategy of the PCM must be certain that the vehicle is standing on a horizontal surface. It assumes that the pump area of a filling station has this type of surface. For this purpose, the signal from the fuel pump and level indicator module is used. If, following “ignition ON”, the fuel level is significantly higher than at the last “ignition OFF”, the PCM assumes that the vehicle is at a filling station and, therefore, is standing on a level surface. The last oil level measurement, that was stored at the last “ignition OFF”, is classified as a valid measurement.

Only this oil level measurement is used for the calculation.

Registering an oil level that is too low

If the PCM has detected refilling of the vehicle fuel tank, the last oil level measurement is compared with the map data. If the measured values indicate an oil level which is too low, a corresponding indicator/text message is displayed on the message center. The indicator/text message illuminates/appears immediately after “ignition ON” and remains active until the next “ignition OFF”. For the next “ignition ON” the lamp/text message is then no longer active.

Note: Even if the engine oil has not been topped up, the indicator/text message is not active again.

Calculation of the oil quality

A strategy is implemented in the PCM that calculates the optimal time for an oil change. This calculation is based on the continuous detection of the engine operating conditions as well as the last valid oil level measurement. If this data reveals an oil change is necessary, then this is indicated via an indicator/text message in the instrument cluster.

Note: After every oil change, the parameters for the oil quality calculation must be reset

06. June 2019 by Ron
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