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Thread: Speedomter, obc, cruise control - Do they get their info from the same source?

  1. #1
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    Speedomter, obc, cruise control - Do they get their info from the same source?

    ‘97 540i. First, I’m running eBay abs sensors and i attributed my my speedometer to this at first, but after making a 700 mile road trop this weekend i am not convinced.

    Situation:

    Speedometer reads erratically. When holdign a constant speed it’s stable but is lethargic to react to changes in speed. The needle does not move as quickly as the car accelerates or decelerates. Sometimes it does not move at all until a consiserable difference in display and actual speed occurs (20+mph).

    As well as being lethargic, the speedometer is inaccurate and inconsistent. If I accelerate from a stop to 80mph the speedometer might display 85 to 90 mph. If i come to a complete stop and accelerate to 80 mph again, the display might be correct or it might be significantly slower. Results differ each time i repeat the exercise.

    ABS light is on periodically and the code is dor the right rear sensor. The code occurs infrequently.

    OBC shows correct speed at all times, confirmed via gps and does not often match the speedometer.

    Cruise control holds correct speed at all times. Hittin resume returns it tothe correct speed and it does not often match the speedometer.

    When the car is stopped the speedometer always reads 0.



    I would appreciate your ideas on this issue. I am assuming the fault kay with the speedimeter itself.

  2. #2
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    Get BMW sensors. Not sure which, it’s been a while, but the right rear does manage the speedo, my brain is telling me, and the left rear handles the cruise control, aside from working as a speed sensor what with traction control and ABS. The speedo has never been completely accurate through all the E39’s that I own, and have owned, and I have owned quite a few. One thing I have learned, stick with factory speed sensors and brake pad sensors.
    Set the controls for the heart of the sun

  3. #3
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    The LR feeds the speedo, odo, and ABS. Likely a bad sensor.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  4. #4
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    That’s conflicting information...if the bc/cruise pull signal from a different source than the speedo then i can more easily accept it as the fault being the sensor the speedo pulls from. But if they all pull signal from the same source then i have hard time understanding how the source could be at fault when the bc and cruise are consistent and accurate.

  5. #5
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    Well, like I said, my brain tells me one thing, but I could be all discumboobulated in the mind and have it backwards. But I always had eratic results when it came to using aftermarket wheel speed sensors and brake pad sensors, switch to oem and enjoy driving the car, rather than chasing after stupid anomalies and wasting your precious time.
    Set the controls for the heart of the sun

  6. #6
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    I switched from the current sensors to oem sensors (admittedly they were used) and back chasing the speedometer thing...it’s not a new issue. I had always assumed it was the sensor and this forum (and numerous other sources) have always told me the speed signal was all from the one sensor. This last weekend was the first time that i noticed that the bc, cruise, and speedometer all appeared to be divorced. Just didn’t make sense to me that two parts of the car know how fast it’s going and the third is just giving it’s best guess.

  7. #7
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    Quote Originally Posted by makenzie71 View Post
    That’s conflicting information...if the bc/cruise pull signal from a different source than the speedo then i can more easily accept it as the fault being the sensor the speedo pulls from. But if they all pull signal from the same source then i have hard time understanding how the source could be at fault when the bc and cruise are consistent and accurate.
    edjack was correct in that the "distance" data comes from the left wheel sensor...that is sent to the ABS unit, then onto the IKE (instrument cluster). See the info below about digital data...and take note of the first topic about DISTANCE signal:

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  8. #8
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    Okay, but do the cruise control and obc get their information from that same sensor? That says it’s sent to the IKE, but does the OBC get it’s information about speed from the IKE? What about the cruise control?

  9. #9
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    Was the instrument cluster LCD cable changed? How was it done?

    If it was done by pulling the needles, the gauge motor may have been damaged. When you pull the needles without holding the shaft down, the return spring hub is pushed down on the shaft. That would cause exactly the symptoms you are describing.

    A quick way to check this is to run an instrument cluster test, either using the buttons (hidden menu, diagnostic mode) or through INPA.

  10. #10
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    I didn’t pull the needles but i don’t doubt it could have been damaged anyway...it didn’t read correctly when i got it (i always attributed this to the abs sensor, though). My fuel gauge and temp gauge also do not work properly. This is part of my reasoning for believing the cluster is damaged and the sensor is working properly, but i didn’t want to list them above to try avoid biasing ideas.

  11. #11
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    Try the self-test, and watch to see if the needles move smoothly through their whole range.

    If multiple gauges are bad, it's likely due to the gauge motors being damaged during repair. If they are just off calibration, that could be due to someone reprogramming the cluster EEPROM and not understanding how the calibration parameters work. (Most clusters are never touched, and only a few types of failures are common. A repaired or replaced cluster has many more possible screw-ups.)

  12. #12
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    Quote Originally Posted by makenzie71 View Post
    Okay, but do the cruise control and obc get their information from that same sensor? That says it’s sent to the IKE, but does the OBC get it’s information about speed from the IKE? What about the cruise control?
    The "OBC" is part of the IKE (instrument cluster electronics).

    And Cruise Control runs through the MFL steering wheel...so again, data/commands for actuation/deceleration/set/stop/resume/etc run through the IKE. And you can see in the chart below that the IKE and the DSC (which would include ABS braking) communicate with each other over the CAN bus.

    I've heard it said that the IKE (in regards to control modules) is considered a MAIN gate-keeper in that just about everything runs to it...or through it as data and commands are sent around the cars communication bus.

    Last edited by Qsilver7; 06-21-2019 at 07:07 PM.
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  13. #13
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    What would cause the speedometer needle to not move at all?

    All tests through service menu and INPA make the needle move fine. Also able to see speed being read by the wheel sensor in the service menu.

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