I attempt a bit of diagnosis on an oil level sensor before I replace it. I do not expect the average DIYer to have a digital storage oscilloscope so not everyone will have the ability to look at a square wave, so Im doing this more because I am just interested in putting the information out there. I do not have a very good scope but its good enough to see a waveform.\r
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You can view the BMW Wiring Diagram System here:\r
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(hint: to get the Java app to work, you have to add that URL to your Exception Site List in the Security tab of the Java applet inside the Windows Control Panel)\r
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Here is the text of the print out I was reading from that site:\r
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Oil Level Warning\r
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Oil level/oil temperature\r
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For the purpose of monitoring the engine oil level, the engine oil symbol lights red to indicate ”oil pressure too low” or yellow to indicate ”oil level too low”. The ”oil pressure too low” warning always has priority. The engine oil symbol lights yellow if the oil level is detected as being too low yet the oil pressure is still maintained. Once recognised, the ”oil loss” status is stored and also indicated while driving until the ignition is switched off (ignition lock in position 0). If ”oil minimum reached” is recognised, this status is indicated for 30 seconds after turning off the engine. Failure of the oil level sensor is signalled after approx. 25 - 30 seconds when the ignition key is turned to position 2 (terminal 15) and oil pressure is applied (engine running). If the sensor fails while driving, this status is not indicated via the oil level warning. This oil level warning has become necessary due to the extension of the oil change cycle. The oil level sensor also supplies a signal for the oil temperature.\r
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Sensor function\r
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The oil level sensor delivers a square-wave signal of variable pulse width and frequency to the engine control unit. The frequency is between 1 Hz and 10 Hz. The measuring principle of the thermal oil level sensor is based on the change in the heating and cooling time of the sensor element located in the engine oil. The High time (pulse ON period) and the Low time (pulse OFF period) correspond to the heating and cooling periods (sensor is cooled by the oil) of the sensor heating element. The High time is dependent on the engine oil temperature and the Low time on the oil level.\r
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The currents and times in the sensor element are also influenced by the current oil temperature and driving dynamics. The oil level is determined from the Low times based on a chareristic map. The level is high at a Low time of approx. 150 ms and low at approx. 550 ms cooling duration. The heating-up time is dependent on the engine oil temperature and is within the time range from 1 ms to 100 ms. The heating-up and cooling-down times must be evaluated for the purpose of assessing the oil level. After a defined warm-up phase, this evaluation recognises two statuses, i.e. ”oil minimum reached” and ”oil loss detected”.\r
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This video is for entertainment purposes only. 50sKid assumes no liability for any repairs or modifications performed by the viewer as a result of the information contained in this video.
