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Thread: ELM 327 , ” headers of 4 bytes”,

  1. #1
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    Lightbulb ELM 327 , ” headers of 4 bytes”,

    Hi estimated friends,
    I have a question, I have a car that have the ECU, it work with KWP ISO 14230-4, and have headers of “ three bytes”, when I set the header by ELM 327, I use the AT command
    AT SH 8011F1
    I need also to establish communication with the ABS ECU, this unit use headers of 4 bytes
    The question is
    How I use the AT SH command to do this….
    What is the format to configured” headers of 4 bytes”, I am using THE ELM 327 V1.4b…The latest version….of 327
    Thank you in advance..

  2. #2
    VENDOR - ScanTool Vitaliy's Avatar
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    The fourth header byte is normally the length byte. With ELM327, you have to put it as the first data byte.
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  3. #3
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    Ok Vitaly, but do you have an example of how sent this order using AT commands?

    Let me explain to you
    The Main ECU unit use the follow KWP message structure to start communication
    81 11 F1 81 04
    and use the folow to wake up
    81 11 F1 3E C1
    and this other to activate the high ventilator of the radiator
    84 11 F1 30 13 07 FF CF

    In all this structures we have headers of three (3) bytes.... and that is easy for me to sent the instructions usin the
    AT SH 80 11 F1
    AT WM 81 11 F1 3E C1

    But here is the point ......
    I have the ABS ECU, that have the follow KWP message structure to start communication
    80 28 F1 01 81 1B
    and use the folow to wake up
    80 28 F1 06 80 28 F1 01 3E D8 4F
    and this other to activate the rear left valve OUT
    80 28 F1 03 30 09 00 D5

    As you can see this structures use header of four (4) bytes, I nned to know how can i send this headers using AT commands, I have buy the ELM327 V1.4b, that allow me to sent this header but I dont know how!!!.

    I Hope your help

  4. #4
    VENDOR - ScanTool Vitaliy's Avatar
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    Argh! I just wrote a detailed reply, but MP3Car forum timed out on me. ((

    Basically, the bottom line is that ELM327 inserts both the checkbyte and the length byte automatically. So after you set up the headers, you provide only the data bytes (no checkbyte and no length byte). When you set up the wake-up message, also omit the check byte.

    You should get a second scant tool and a Y-cable, so you can see what you are actually sending.

    Keep us posted on your progress.

    Vitaliy

    PS What car is this, and where did you get the information about the messages?
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
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  5. #5
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    Ok my friend, I understand the ELM327 insert the length and the check sum byte automatically, but the question is how The ELM understand that I want to send a header of 3 or 4 bytes….
    The version that actually I have for the ELM 327 is the V1.0, and this only send headers of 3 bytes, I set up the header with AT SH , for example:
    >ATSH 8011F1
    OK
    >ATWM 8111F13E
    OK
    >81
    SEARCHING...
    C1 EF 8F
    All this instructions are for the MAIN ECU, when I sent the instruction to the ECU, I can see with a second scanner and using the Y cable that I have the follow data on the “k line”
    Example 1
    Instruction sent:
    >301007FF
    70 10 07 00
    “k line capture”
    84 11 F1 30 10 07 FF CC
    Example 2
    Instruction sent:
    >30100790
    70 10 07 00
    “k line capture”
    84 11 F1 30 10 07 90 5D
    Ok, As you can see the ELM automatically insert in the first byte the length of the message and calculate the check sum.
    All this is right for the MAIN ECU of this car, that work of this way right….
    The point is that the ABS ECU, work with headers of 4 bytes, I am waiting for the arrival of my new Tool scan that have the ELM 327 V 1.4b , this version allow me to sent headers of 4 bytes.
    How I make that the ELM understand that I want to send headers of 4 bytes this time..???.
    When I see the “k line of the ABS” I see:
    80 28 F1 03 30 09 00 D5
    80 28 F1 03 30 08 00 D4
    And more like this, but the point is that the first byte keep always on 80, and the length byte appears like the 4 byte, and after that the data bytes, and finally check sum.
    Then I need to know how to make that the elm sent this structure of 4 and not 3 bytes….for the ABS ECU?.
    PS: This car is a LIFAN 320, and I have obtained the information of the data structures by sniff the bus with my Y cable and using other Scan ELM327 like monitor.
    PS2: like advice to avoid that the forum time out me….I wrote on a text editor first and copy all to the window of the forum finally. That allow me to sent extend messages.

  6. #6
    VENDOR - ScanTool Vitaliy's Avatar
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    Quote Originally Posted by OPMOTOR View Post
    Ok my friend, I understand the ELM327 insert the length and the check sum byte automatically, but the question is how The ELM understand that I want to send a header of 3 or 4 bytes….
    The version that actually I have for the ELM 327 is the V1.0, and this only send headers of 3 bytes, I set up the header with AT SH , for example:
    >ATSH 8011F1
    OK
    >ATWM 8111F13E
    OK
    >81
    SEARCHING...
    C1 EF 8F
    All this instructions are for the MAIN ECU, when I sent the instruction to the ECU, I can see with a second scanner and using the Y cable that I have the follow data on the “k line”
    Example 1
    Instruction sent:
    >301007FF
    70 10 07 00
    “k line capture”
    84 11 F1 30 10 07 FF CC
    Example 2
    Instruction sent:
    >30100790
    70 10 07 00
    “k line capture”
    84 11 F1 30 10 07 90 5D
    Ok, As you can see the ELM automatically insert in the first byte the length of the message and calculate the check sum.
    All this is right for the MAIN ECU of this car, that work of this way right….
    The point is that the ABS ECU, work with headers of 4 bytes, I am waiting for the arrival of my new Tool scan that have the ELM 327 V 1.4b , this version allow me to sent headers of 4 bytes.
    How I make that the ELM understand that I want to send headers of 4 bytes this time..???.
    When I see the “k line of the ABS” I see:
    80 28 F1 03 30 09 00 D5
    80 28 F1 03 30 08 00 D4
    And more like this, but the point is that the first byte keep always on 80, and the length byte appears like the 4 byte, and after that the data bytes, and finally check sum.
    Then I need to know how to make that the elm sent this structure of 4 and not 3 bytes….for the ABS ECU?.
    PS: This car is a LIFAN 320, and I have obtained the information of the data structures by sniff the bus with my Y cable and using other Scan ELM327 like monitor.
    PS2: like advice to avoid that the forum time out me….I wrote on a text editor first and copy all to the window of the forum finally. That allow me to sent extend messages.
    I assure you this was all very eloquently explained in my original message, with detailed examples. And normally I copy the contents in case of a forum timeout, but that one time I hit "Submit", got distracted, went to do something else, and -- ARGH!!!!

    The new version of ELM327 will not change the first byte, it will insert the length byte as the first byte of data, when you set the first byte of header to 0x80. Do you understand now?

    So when you set the headers like this..

    ATSH 80 28 F1

    ..and then send your message like this...

    30 10 07 90

    ..you will see the message on the bus like this ...

    80 28 F1 04 30 10 07 90

    ..plus whatever the checkbyte is (sorry, I'm away from my workstation).

    Best regards,

    Vitaliy
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
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  7. #7
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    Lightbulb

    Excellent, excellent Vitaliy thank you very much, i have all so clear now..., *** soon
    as arrive my new chip ELM 327 V.1.4b y will use the instructions that you sent me,

    Just one thing, very strange, looking the "k line" putting the ELM327 like monitor....

    I see:

    the follow wake up

    80 28 F1 06 80 28 F1 01 3E D8 4F

    that is very strange because when i check the check sum for
    80 28 F1 06 80 28 F1 01 3E D8 this is = 4F

    and checking the check sum for
    80 28 F1 01 3E this is = D8

    For me is strange that the professional scanner ( V30 model from Autoboos ), sent
    this REDUNDANT message that contain a completely normal message inside other message.
    But I will experiment with
    80 28 F1 01 3E
    And the
    01 00
    But what do you think about but the 80 28 F1 06 80 28 F1 01 3E D8 4F structure.


    Thank you very much

  8. #8
    VENDOR - ScanTool Vitaliy's Avatar
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    I noticed the "message inside a message" in your original post. Very strange, but I don't have an explanation.

    p2psmurf is the expert on European OBD, perhaps he can comment?
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  9. #9
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    Quote Originally Posted by Vitaliy View Post
    PS What car is this, and where did you get the information about the messages?
    I'm sorry for digging up a 1 year old post but I'm looking for some information and I can't find it.

    I would like to learn more about all sorts of messages that can be send to ECU, EBCU/ABS, etc. I don't suppose you guys know where a hungry developer can find this sort of information for free?

    I'm finding some information regarding ECU communication but I'm looking for something with every little tid-bit of information to sink my teeth into, but anything will do.

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