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Thread: DIY: Eliminate Speedometer Error doityourself

  1. #1
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    DIY: Eliminate Speedometer Error doityourself

    Requirements
    • BMW Scanner 1.4 (or any other means for editing the Cluster EEPROM). DIS, NCS Expert, SSS, etc. are not sufficient for this one.
    • CI06 or newer cluster for non-M, and CI23 or newer for M (I think this corresponds to 2002 or 2003 and newer for both groups)
      • It is possible to do this on early clusters too, but the software is quite different. I can research if a few of you send me a dump of your cluster EEPROM. Also tell me the amount of error you've measured (between the needle and digital test)
    • Some common sense



    As most of you know, E46 clusters tend to be optimistic. What you may not have known is that the DME and Cluster know the exact speed; the error is deliberate on BMW's part. There have been a few ways to correct this in the past; one way is to just trick the cluster into thinking you have smaller tires, but this can screw up things like MPG and average MPH calculations. Another way was to rescale the cluster curve itself, but this required a decent bit of trial and error and it was just fooling the cluster into thinking the scale was larger.

    After studying M and non-M EEPROM files, here's what I found -- there is a function deliberately designed to increase the speed by a certain ratio. In the non-M, the displayed speed is the real speed + 5.7%. In the M3, the error is a massive 8.9% -- completely unacceptable IMO.

    So here's what you do.

    1. Start up the PASoft software and load your IKE. Read off the EEPROM.
    2. Now, in the built in hex editor, look for the following hex string (pick the appropriate one for your model).

      Code:
      E46 M3:     03 00 2D C8 00 31 D6
      Non-M:      03 00 23 C8 00 25 CC
    3. Change it to the following

      Code:
      All models: 03 00 01 C8 00 01 CA
    4. Save the file, and flash the EEPROM back to your cluster.


    Done. If you have stock diameter tires, your speedometer should be almost 100% accurate

    If you're curious as to how the change works, the bytes I change are used as a ratio. 0x25 = 37; 0x23 = 35. 37/35 = 1.057, or a 5.7% error. I am not sure what the 0xC8 (200) value represents; I think it might be an upper limit to the allowed error (5.7% until the error reaches 20 km/h). That last byte is simply a checksum (XOR all the values together, and then XOR with 1)

    If you have an old cluster, please send me your EEPROM. I can't promise I'll figure out how to do the change there, but I'll try. Also, if there are any Japanese members here, please send me a dump of your cluster. In the E39, the Japanese values for the cluster are 100% accurate; I suspect the same holds true for the E46. It would be interesting to see how BMW configured the cluster.

    Give me feedback; so far in my testing it agrees with GPS, but it's always nice to have others confirm too

    Oh and I should thank geargrinder -- he got me interested in looking at this stuff again, and helped fix a few of my earlier mistakes

  2. #2
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    Thanks for being open-minded and sharing your findings Terra. I noticed almost all US cars have a percentage error that is always higher on the cluster than actual speed.

  3. #3
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    Quote Originally Posted by derbo View Post
    Thanks for being open-minded and sharing your findings Terra. I noticed almost all US cars have a percentage error that is always higher on the cluster than actual speed.
    Not a problem! I always figured these forums are about sharing info. Anything I figure out will end up here (or any of the other forums). Giving back to the community is the least I can do

    Wish I still had my ZHP so I can test a few more things and post them

  4. #4
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    Quote Originally Posted by terraphantm View Post
    Not a problem! I always figured these forums are about sharing info. Anything I figure out will end up here (or any of the other forums). Giving back to the community is the least I can do

    Wish I still had my ZHP so I can test a few more things and post them
    Shame you arent close by, I would've lend my car for some testing. I want an M3 cluster + working oil temp gauge and correct offset water temp and fixed speedo. haha. If only the warmup lights could set it to 6800rpm too for redline.

  5. #5
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    Terra, what do you know about setting BC_V_KORREKTUR to "nicht_aktiv" via NCSExpert? I did that & my speedo error went from ~3.5 mph (probably exactly the 5.7% you mention) to only 1 – 2 mph. It didn't completely remove the error, but greatly reduced it. Any idea on what your method would do in my case?

    Travis | '04 ZHP sedan 6MT | WeĭssLĭcht AEs | BMW clears | Plasti-Dipped grilles | BMW Perf. intake | TMS Power Pulleys | DIY aux-in | !CDV
    Sprint Booster w/Sport button | Mich PS A/S 3 (245 sq) | M3 front sway | Z4M LCABs | Beisan VANOS rebuild | GAS DISA rebuild | BMW diag. PC

  6. #6
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    Terra just found your thread with geargrinder on bimmerforums. Very good information you guys have there with the XOR logic and figuring out the byte information.


    I will have to invest in a PA Soft soon.

  7. #7
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    I'll be testing this out when I get out of work today. Thanks for the info!



    Sent from my DROID RAZR MAXX HD
    BP
    2005 330i ZHP / 6MT
    Imolarot / Naturbraun



    It's not the car you drive, it's how you drive it.

  8. #8
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    I have PA soft but build date of 12/2000 so I'm assuming this will not work for me?

    Sent from S4

    '01 330i

  9. #9
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    Good info. You mention stock tire sizes, as the ZHP uses staggered, how do that play into the speed calculation and what if you go square?
    Randeaux/Rando/John/jr - '06 Cic ZHP; Southern California
    "ZHP or not, I still like you"


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  10. #10
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    Quote Originally Posted by johnrando View Post
    Good info. You mention stock tire sizes, as the ZHP uses staggered, how do that play into the speed calculation and what if you go square?
    The overall diameter of the factory staggered tires sizes are the same so it would not be affected.

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