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Thread: AutoTap ODB-2 cable...

  1. #11
    Newbie
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    Nov 2004
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    11
    nothing just yet other than i am going to use this AutoTap interface to communicate with my OBD-2.

  2. #12
    Variable Bitrate Leddy's Avatar
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    What are you using to sniff the traffic?
    2001 Pontiac Grand Prix GTP Sedan (Sold)
    2007 Scion tC
    WhereIsMyGPS.net Online Tracker
    http://www.cardomain.com/id/leddy

  3. #13
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    Nov 2004
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    I stumbled on it by accident -- my USB KeySpan driver has some diagnostics built in.
    It'll log the traffic
    I just wish it could go to a log file rather than just a window which can't be copied from either

  4. #14
    Variable Bitrate Leddy's Avatar
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    Ok I've been doing some research...

    Request: 11/22/2004 6:38:39 PM.
    00 01 68 6A F1 00 00 00 00 00 00 00 06 80 00 04
    Answer: 11/22/2004 6:38:39 PM.
    01 01 01 04 1B 01 01 00 01 01 00 0C 00 00 04

    If Autotap is not connected it will retry with no answer.

    Once verified it will send a request for VIN there are three parts
    01 6C 10 F1 3C 01 00 00 00 00 00 05 0F 00 04
    01 6C 10 F1 3C 02 00 00 00 00 00 05 0F 00 04
    01 6C 10 F1 3C 03 00 00 00 00 00 05 0F 00 04

    It then looks like it starts gathering parameters supported and DTC's

    I then added RPM(with car off) as
    01 68 6A F1 01 0C 00 00 00 00 00 05 00 00 04


    So I'm drilling down.
    2001 Pontiac Grand Prix GTP Sedan (Sold)
    2007 Scion tC
    WhereIsMyGPS.net Online Tracker
    http://www.cardomain.com/id/leddy

  5. #15
    Variable Bitrate Leddy's Avatar
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    Anyone feel like writing a small vb app to allow us to copy into it the strings posted above and sending as bytes and displaying results?
    2001 Pontiac Grand Prix GTP Sedan (Sold)
    2007 Scion tC
    WhereIsMyGPS.net Online Tracker
    http://www.cardomain.com/id/leddy

  6. #16
    Variable Bitrate Leddy's Avatar
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    Mar 2004
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    I'm about to fall asleep here so it will be interesting to read this in the morning. A friend of mine wrote a VERY primitive app for me to do some testing. That along with a plethora of information on the VPW protocol is amazing. I think I've been reading non stop straight.

    I connected my autotap V1 cable to my car and fired up test program. I bypassed all inits and PID queries.

    GM uses VPW and a 15 byte packet to communicate with the PCM.

    I wanted to test RPM so I sent the following to com1
    01 68 6A F1 01 0C 00 00 00 00 00 05 00 00 04
    my response was
    01 48 6B 10 41 0C 0C EC 00 00 00 07 00 00 04
    ^^^^
    Those are the significant bytes for RPM as it's a 2 byte return
    Now lets figure it all out:
    0C = 12(decimal)
    EC = 236(decimal)
    12 * 236 * .25 = 708

    My car was idling at 708 RPM
    Each PID has it's own way of calculating it's return to it's "real" value.
    This was all done with my autotap cable w/o the autotap software. Just a "homegrown" serial com program. You just have to know what data to send and how to format it and it's return. That information is readily available on the net.
    2001 Pontiac Grand Prix GTP Sedan (Sold)
    2007 Scion tC
    WhereIsMyGPS.net Online Tracker
    http://www.cardomain.com/id/leddy

  7. #17
    Constant Bitrate
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    Mar 2004
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    Metamora, MI
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    Leddy,
    The "format and it's return" is called the transform in the industry. For each data element there is a cooresponding transform that is applied to the return for the "human speak" value. Each OEM provides tables with these transforms to the service aftermarket. Part of the value of the autotap (or other scan tool software) is the very significant amount of work it takes to put the unique transforms into a database for an application to use correctly. Not to mention the validation effort to make sure that the OEM provided the correct transform.

    That's one of the key reasons why one scan tool costs X and another costs 10X.

  8. #18
    Variable Bitrate Leddy's Avatar
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    Mar 2004
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    Yes just getting the data isn't really the hardest part. It's knowing the formulas
    2001 Pontiac Grand Prix GTP Sedan (Sold)
    2007 Scion tC
    WhereIsMyGPS.net Online Tracker
    http://www.cardomain.com/id/leddy

  9. #19
    Newbie
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    Nov 2004
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    i'm still working on my java app to do the same basic thing, but i have big plans ... just need to keep going.

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