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  1. #1
    Lifetime Member GMPX's Avatar
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    Apr 2003

    Exclamation CVN's Explained.

    Hi All,

    Something we are asked about quite often is to do with CVN's. What are they? What do they do? So I thought I would do a quick explanation. Scattered throughout this forum is various discussions on it, so it was time to summarise in to one thread.

    Q - What is a CVN?
    A - CVN stands for "Calibration Verification Number", this is a fancy name for checksum. What the ECM (or TCM) does is add up all the numbers within each segment of the flash memory, the total of those numbers is what the CVN equals. This allows people with a TechII to quicky check the data in each segment is correct or unaltered (eg, the CVN matches a known program).
    If any data is altered within the segment then the checksum (CVN) will change or not match what it originally was.

    The CVN can also be used by tuners to uniquely identify their own calibrations without needing to read out the ECM / TCM.
    EFILive allows workshops (or stream owners) to modify the CVN to whatever value they desire.
    As an example, a stock E38 CVN list might be as follows -
    Segment Name       Part Number CVN
    Operating System   12612381    50D6
    Engine Operation   92200744    26BA
    Engine Diagnostics 92200743    0B9F
    Fuel System        92196978    D0EB
    System             92200742    16E2
    Speedometer        92196106    C405
    A tuner might wish to change each CVN to a pattern they can quickly recognise -
    Segment Name       Part Number CVN
    Operating System   12612381    AAAA
    Engine Operation   92200744    BBBB
    Engine Diagnostics 92200743    CCCC
    Fuel System        92196978    DDDD
    System             92200742    EEEE
    Speedometer        92196106    FFFF
    Segment Name       Part Number CVN
    Operating System   12612381    50D6
    Engine Operation   92200744    1001
    Engine Diagnostics 92200743    1000
    Fuel System        92196978    2004
    System             92200742    1000
    Speedometer        92196106    3000
    In the last example the CVN of the calibration segments could be used to indicate a version of the tune, so Engine Operation v1.001, Fuel System v2.004.

    CVN editing is only available to customers who have the stream enabled for the controller they are trying to correct the CVN on. Anytime the CVN is altered from the stock value the vehicle would no longer meet EPA / CARB emissions regulations. Please keep that in mind if you are thinking of putting in some custom patterns like those above.
    You must be very careful not to alter the CVN's to a value already used by the manufacturer, please see page 99 of the SAE HS-3000 purple book for more on this.

    How to alter the CVN in EFILive -
    Click on the CVN Tab (with a E38,E40,E67,T42 or T43 file loaded and active stream for that controller).
    Click on the CVN value you wish to alter and enter in the new number (using only letters A - F and numbers 0 - 9). Hit enter.
    Then click the 'Update' button and save / reflash the file.

    Many early controllers did not support CVN reporting, it really came to light after about 2006, CVN customisation for the Bosch Diesel ECM is not possible.

    Last edited by GMPX; November 16th, 2008 at 11:52 AM. Reason: Formatted CVN's
    I no longer monitor the forum, please either post your question or create a support ticket.

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