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Originally Posted by d1saster
I apologize for reviving an old thread but it seems that the above information is the solution for fixing the speedometer accuracy and maybe missed by many interested. Thanks to "tboudre" for finding the magic number for K_ZAHL_TACHO A4,61=24996. It appears that number has to be less than 25000 otherwise the cluster returns errors.
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Quote:
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Originally Posted by beastpilot
The BMW "offset" in the speedometer has always annoyed me. I had the correct speed coded into my cluster digital display, but since I have a HUD I never look down at it. I really wanted the HUD to be right.
I figured out how to correct the speedometer in the car. This corrects both the speedometer needle and the HUD if you have one. The cruise works and follows the displayed speed.
Note that after you do this, if you "true speed" for the digital cluster display, it will be high. So code it for "corrected speed", or turn it off now that it's just a copy.
To do this you need to know about coding. Sorry, but I can't get you all set up there. I can help you once you know how to code though.
Tools needed:
NCS Dummy
NCS Expert
Excel
1) Pull your trace file from KOMBI with NCS Expert
2) Open the trace file in NCS Dummy
3) Look for K_ZAHL_TACHO in NCS Dummy. Look up the DATA for the wert_xx that represents your car. In an E60 M5, this is wert_03, and the DATA is "99,58"
4) Open the attached Excel spreadsheet. Put the DATA in cell B2, next to "BASE".
5) This will calculate a K_ZAHL_TACHO_KOMPL in cell C2. Make sure this matches the wert_xx in NCS Dummy for K_ZAHL_TACHO_KOMPL. In an E60 M5 this is 66,A7.
6) Now you can create your adjustment. In the middle of the spreadsheet are all the adjustments in 0.5% increments. You can pick any of these. Or you can go to the bottom and put in any number you want for "arbitrary"
7) In NCS Dummy choose "clear" under the browse button for the trace file
8) Scroll down to K_ZAHL_TACHO in NCS Dummy and right click on it. Choose ADD PARAMETER. Call it wert_xx with the value one higher than the last one. For data, put in the data for K_ZAHL_TACHO from the adjustment row you want.
9) Repeat #8 for K_ZAHL_TACHO_KOMPL
10) Load the trace file again in NCS Dummy. Switch K_ZAHL_TACHO and K_ZAHL_TACHO_KOMPL to the new wert selections.
11) Change BC_V_KORREKTUR and BC_DIGITAL_V_KORREKTUR to nicht_aktiv
12) Program the MAN file via NCS Expert
DRIVE!
I've done this a few times in my E60 M5, and 4% was the right correction. It reads dead on to the GPS in my phone at 40 MPH and 75 MPH. I haven't tried at higher speeds.
For the M5, this is a K_ZAHL_TACHO of 24,5C and K_ZAHL_TACHO_KOMPL of DB,A3
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https://www.m5board.com/threads/corr.../#post-5559466
I couldn't understand how to calculate the correct value for my car so I found the original post. Also attaching the excel file in case it becomes unavailable from the server in the future. Just delete .txt extension.
