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Thread: O2 sensor testing

  1. #1
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    O2 sensor testing

    Hello all, hope your wrenching is going well.

    When testing an o2 sensor using a multimeter do I need to leave the sensor plugged in and back probe it to get the readings? The Bentley manual is not completely clear about that step.

    Thanks as always!

  2. #2
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    You do not need to leave it plugged in. They generate their own voltage. Keep in mind they need to be up to temp in order to do so though.
    ______________________________
    1992 750iL

  3. #3
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    Best is with running engine, then you can see the V moving up and down and the speed of the moving, you can test it on the DME pins with running engine. Remove the black plastic cover in engine bay from the e-box. Remove the plug connector from the DME, measure for M60 DME at pin 12 and 39 for cylinder row 1-4 and pins 13 and 40 for cylinder row 5-8. Pin numbers are shown inside the MOTRONIC.Please recheck/verify pin numbers with your Bentley Repair Manual for your model.
    http://www.yvesreiser.lu/photos/lambda/S8000490.JPG
    http://www.yvesreiser.lu/photos/lambda/S8000491.JPG
    M30b30 engine with Bosch Motronic end # -150 or -179: Pin 28 is Lambda, Pin 10 is ground for that. After engine is at operating temperature = the O2 sensor is hot/operating temperature, the sensor starts to regulate. The value should move between 0,1 and 0,9 Volt a min. within 1 second, the more the better, otherwise they are too slow. Till the sensor starts regulatinng = not yet at operating temperature, the value measured is approx 0,5 Volt, in case measured value is more than 1,3V, - oxy sensor is defective.
    M1.3 DME pinout http://www.e38.org/e32/m1_3.pdf
    Pins on other DMEs:
    Motronik Bosch -352 M70 : Lambda Pin 70, and Lambda ground Pin 71
    Motronik Bosch -156 M70: Pin 28 Lambda signal (+) and Pin 10 (-), cable colors as per Bentley Pin 28: black, Pin 10: yellow, DME pinout https://www.europeantransmissions.co...out1988_90.pdf
    Motronik Bosch -404 M60B30 and M60B40 : Zyl. 1-4 Pins 13 (SW) = right side of engine and 40(GE), for 5-8 12(SW) and 39 (GE) for left side bank.

    I have a DIY tester which I can plug in between the original connectors of the o2 sensor under the car, then I start the engine, wait till it get's at operating temperature and then I can see the lights flickering/moving, here a youtube https://www.youtube.com/watch?v=K8miz_1aHYw
    at the beginning the sensor was not yet hot enough, the longer the engine runs, the better it becomes.
    Actually it is a DIY exhaust, gas, oxygen monitor kit, which we modified, soldered on original O2 sensor plugs for both sides (from/to engine), so we can install it inline. That was more than 10 years ago, nowadays with the modern equipment it is easier to monitor.
    Last edited by shogun; 06-10-2019 at 02:11 AM.
    Shogun tricks and tips for the E32 series are HERE!

  4. #4
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    Thanks for the assistance!

    Oddly enough my CEL hasn't come on since yesterday when I used the multimeter to properly calibrate my throttle position sensor per Bentley manual spec. I did it "by feel" last time and that's generally not the best way.

    Hopefully I've finally got this lamda sensor code put to rest.

  5. #5
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    CEL is back! I had some extra time at work to test the O2 sensor at the DME and found the voltage to be -.01v warmed up and at idle. When I would give it some throttle the number would spike to 0.7v before quickly bouncing back to -.01v.

    I'm not exactly sure what this means, but I am confident that I had performed the test correctly.

  6. #6
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    Do some more tests. The value should move between 0,1 and 0,9 Volt a min. within 1 second, the more the better, otherwise they are too slow. Till the sensor starts regulating = not yet at operating temperature, the value measured is approx 0.45-0,5 Volt, in case measured value is more than 1,3V, - oxy sensor is defective. Here some more info: Oxygen Sensor Testing http://www.autodiagnosticsandpublish...r-testing.html
    https://www.youtube.com/watch?v=jN0LlVpDZNo

    If the O2 sensor only produces a low- or high-voltage signal, either you have an engine performance issue or the oxygen sensor stopped working. To verify sensor operation, conduct the next two tests.........
    https://axleaddict.com/auto-repair/H...-Oxygen-Sensor

    In case you buy a new sensor, buy a good brand one like Bosch, NTK, Denso etc., not that cheap no name ones. Last year one of my wrenching buddies ordered 2 new ones for his M70, cheap no name from the well known auction house, one new one of them had an internal shortage, before we installed it we tested it, and we even installed the bad one just to see what happened and the engine ran terrible.
    Shogun tricks and tips for the E32 series are HERE!

  7. #7
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    Ah! Thanks the video was very helpful. I was performing the test incorrectly and had been probing the O2 sensor ground instead of just grounding it on the frame. Just to confirm, I should be probing pin #28 and a ground to measure the voltage fluctuations for the O2 sensor?

    And to your point it could very well be my sensor which I did get from a junkyard. The previous sensor that I had purchased was a cheap-o and I unfortunately destroyed the original sensor during removal (SST's are important!).

  8. #8
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    On DME Motronic M30b30 engine with Bosch Motronic end # -150 or -179: Pin 28 is Lambda, Pin 10 is ground
    Shogun tricks and tips for the E32 series are HERE!

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