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Thread: RPM and speedometer false reading

  1. #1
    Join Date
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    RPM and speedometer false reading

    Hello.

    I have a 99 e39 m52tub25 touring and i have a little problem with the tachometer and speedometer.



    Analog read.png
    Now as you can see in the picture above, i am reading off the analog values
    from the instrument cluster.. i am idling, so the speed is of course 0, but the rpm is also 0.


    CAN read.png

    In this picture above, i am reading off the CAN signal values,
    this is also within the instrument cluster.
    Here you can see that instrument cluster, can read off the engine speed from the can signal.


    MS42read.png
    In this picture i am reading off the values from the ECU itself,
    here you can see that he sends out the correct rpm,
    and since im just idling, the speed is still 0..

    Now the speedometer,
    works but its response time is somewhat slower than normal,
    and takes a little bit of time to drop to a lower speed.

    The RPM however is incorrect, if i rev it to say 2k, the needle will be slightly above 1k, so its incorrect by 700-1000 rpm

    But it is a little bit strange because i can see the actual rpm in the CAN signal,
    which is as i said through the instrument cluster interface,
    so its like why does he not "forward" the can signal when he knows its there ?
    does this mean that the gauge(s) it self is beginning to go bad?
    Last edited by Vega2k; 04-20-2018 at 10:16 PM.

  2. #2
    dworthy's Avatar
    dworthy is offline Wagon meister :) BMW Tech Expert
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    What if any error code or codes do you have in any of those modules?

    As for the speed, I would have a look in the ABS/AST+T module and see what the wheel sensors are sending. Normally I like to raise the car and spin each wheel to see what the threshold is, typically around 2kph is normal before it starts to read. That can be cause of the speed problem. If that all works out well, then yes check for error codes in the IKI to see there are any.
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  3. #3
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    It would appear that you have a very similar issue to one I just had with a customer car:

    https://www.bimmerforums.com/forum/s...ly-weird-issue

    However, of course, your rev counter is reading incorrectly, though the engine computer is outputting the correct figure. Therefore, I'd have to guess that the signal for engine speed and vehicle speed on your car is getting corrupted a bit earlier, in the instrument cluster, than the Z4 I was dealing with.

    Note that, on your car, the instrument cluster does not act as the gateway module for any signals, so it's not redistributing information to other modules:

    https://screenshots.firefox.com/zTOb....prodemand.com

    In short, I'd have to believe that your instrument cluster is defunct.

    Check whether the ABS/DSC is reading the correct engine speed; and the DME reading the correct road speed.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  4. #4
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    Thank you both for your replys
    It has been some months now but i thought id give an update.

    I actually gave up trying to fix this after your reply bmwdirtracer and reading your thread.. but the problem was still was bothering me..

    This week ive been trying various stuff of recoding it to stock, recalculating eeprom and so forth in believing maybe it was a software issue.. it was of course not.
    but yesterday I managed to get this one sorted out.

    I got over this thread http://forum.e46fanatics.com/showthread.php?t=865790
    Where this guy is replacing his gauge bezel and after re installation his needles were off its course, turns out he needs to re calibrate the needles.

    I followed up what mr roofless advised and thought why not give it a try.

    And boom, the rpm and speedometer now is working as they should

    speedometer was a little inaccurate at first, it was reading 71 km/h when the actual was 57 km/h, reading from a gps.
    So i turned the ignition off, and turned the speedometer needle counter clockwise carefully into its resistance.
    After that it was spot on. needle readings became accurate to the actual speed.

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