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Old Sun, Aug-25-2013, 12:19:14 PM   #41
matthias2280
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Anyone want to loan out the tools/cables necessary to do this mod? I'm sure we can work something out...
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Old Sun, Aug-25-2013, 02:29:01 PM   #42
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Default Re: DIY: Eliminate Speedometer Error

So, I was interested in figuring out just how far out my speedometer was. I drove a good amount of miles using a GPS to do so. With cruise locked at 80 in the car the GPS would indicate 77 or 78mph, this seems about the same as every other car I've driven and compared to a GPS. Seems odd, I'd hate to think the GPS is off as well, because I've definitely been on the highway going a reasonable speed yet getting passed by a ton of cars.
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Old Sun, Aug-25-2013, 05:58:11 PM   #43
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Default Re: DIY: Eliminate Speedometer Error

Quote:
Originally Posted by matthias2280 View Post
Anyone want to loan out the tools/cables necessary to do this mod? I'm sure we can work something out...
I received my software and cable and (as I figured) the cheap $30 version is a chinese knockoff. However I'm sure the hardware will work fine with the real software I just can't get the drivers to work so my computer will read it. I did try and download new drivers but they don't work either. If you're up for trying I could send you what I have

I'm also tempted to just buy the full version so I know what I'm getting and any software support as well
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Old Mon, Aug-26-2013, 05:37:14 PM   #44
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Default Re: DIY: Eliminate Speedometer Error

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Originally Posted by Mr. Black View Post
I received my software and cable and (as I figured) the cheap $30 version is a chinese knockoff. However I'm sure the hardware will work fine with the real software I just can't get the drivers to work so my computer will read it. I did try and download new drivers but they don't work either. If you're up for trying I could send you what I have

I'm also tempted to just buy the full version so I know what I'm getting and any software support as well
I'll give it a try. Wanna send the stuff to me ?
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Old Mon, Aug-26-2013, 06:18:03 PM   #45
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Default Re: DIY: Eliminate Speedometer Error

Glad I found this thread, I just got my M3 and I was wondering why my speedo was reading so high... Yet another Mod to add to the list! thanks for the info OP =)
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Old Mon, Aug-26-2013, 06:35:56 PM   #46
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Default Re: DIY: Eliminate Speedometer Error

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Originally Posted by matthias2280 View Post
I'll give it a try. Wanna send the stuff to me ?
Sure, just pm me your address
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Old Sat, Sep-14-2013, 01:36:03 PM   #47
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Default Re: DIY: Eliminate Speedometer Error

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Originally Posted by terraphantm View Post
I posted this DIY on e46fanatics, and figured you guys would like it too since the M3 error is huge. Left the non-M info there since some of you may have non-Ms

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
Very, very, very good work! I have an e46 Compact rebuilt with S54B32 and complete e46 m3 drivetrain +++. The car is also equipped with e46 m3 instrument cluster. The almost 9% speedometer error was driving me crazy and not acceptable IMO.

Changed, as you suggest, the
Code:
03 00 2D C8 00 31 D6
to
Code:
03 00 01 C8 00 01 CA
and the speedometer is now almost dead accurate, i.e approx +1% error running 225/40/18 front and 255/35/18 rear.

Your work is very much appreciated.

Thanks for sharing!!!!
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Old Sat, Sep-14-2013, 01:41:49 PM   #48
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Quote:
Originally Posted by e36 323ti View Post
Very, very, very good work! I have an e46 Compact rebuilt with S54B32 and complete e46 m3 drivetrain +++. The car is also equipped with e46 m3 instrument cluster. The almost 9% speedometer error was driving me crazy and not acceptable IMO.

Changed, as you suggest, the
Code:
03 00 2D C8 00 31 D6
to
Code:
03 00 01 C8 00 01 CA
and the speedometer is now almost dead accurate, i.e approx +1% error running 225/40/18 front and 255/35/18 rear.

Your work is very much appreciated.

Thanks for sharing!!!!
Pictures of car in question !
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Old Sat, Sep-14-2013, 02:39:35 PM   #49
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Default Re: DIY: Eliminate Speedometer Error

Quote:
Originally Posted by cyberlando View Post
Pictures of car in question !
Pictures and info here: http://www.bmw-syndikat.de/bmwsyndik...BMW_-_E46.html
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Old Sat, Sep-14-2013, 04:27:27 PM   #50
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Default Re: DIY: Eliminate Speedometer Error

OK, I don't really know anything about changing anything but my question is this: What you are saying is that if I set my cruise at say 80mph, I am actually only going around 74mph right? I have noticed that when I have gone by those meters that the cops put out saying how fast you are going that it usually says I am going about 6mph slower than what my speedo says. I didn't realize there was an actual reason for it, I thought it was because I had 19" wheels or something
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Discussing DIY: Eliminate Speedometer Error in the Coding and Tuning Forum - Discuss all avenues of coding and tuning here! at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)