Results 1 to 5 of 5

Thread: Doubts about 29-bit CAN OBD protocol

  1. #1
    Newbie
    Join Date
    Dec 2009
    Location
    spain
    Posts
    5

    Doubts about 29-bit CAN OBD protocol

    According to OBD-II & ISO15765, for instance, a test equipment to request on Mode 1 engine RPMs must send the next frame in the 11-bit CAN protocol;
    ID: 7DFh Data: 02h 01h 0Ch Aah Aah Aah Aah Aah
    And the response of the Engine control module unit will be similar to:
    ID: 7E8h Data: 04h 41h 12h 70h 0Ch Aah Aah Aah

    I think I have pretty clear the 11-bit CAN protocol for OBD. The identifiers used are clearly defined in Table 3 of ISO15765-4.

    My question is about the 29-bit CAN protocol.
    When the test equipment want to ask about the RPMs in mode 1, what frame is used? Is it correct the next frame?
    ID: 18DB33F1h Data: 02h 01h 0Ch Aah Aah Aah Aah Aah

    On the other hand, what will be the response frame of the diagnosis unit? Is it correct the next frame?
    ID: 18DAF1xxh Data: 04h 41h 12h 70h 0Ch Aah Aah Aah

    That is, it uses 29-bit identifier defined in Table 5 in ISO15765-4 and the data would be the same as in the protocol of 11 bits.
    What usually takes xxh value in the ID of the response?


    I tried to learn more of this 29-bit protocol sniffing the frames exchanged between my test equipment and a Volvo S-60 because I had read in some forums that Volvo was one of the few manufacturers that used this 29 bit- protocol . But my surprise was when I saw that it used the 11-bit protocol . What type of OBD protocol is used by VOLVO ? 11 or 29 bits?

    On the other hand, trucks or farm machinery that is manufactured using ECUs according standard J1939 usually have a diagnostic connector similar to the sport vehicles. Despite using the J1939, Can you connect a test equipment and try to make a test in the track in a similar way to you do in a sport vehicle?. Do they use the 29-bit protocol ?

    There are many questions at once, but I would be very grateful if someone can help me to clarify the use of 29-bit CAN OBD or can tell me any website where I can clear my doubts.

    Thanks in advance

  2. #2
    Constant Bitrate joeyoravec's Avatar
    Join Date
    Oct 2005
    Location
    Livonia, MI
    Posts
    205
    Quote Originally Posted by fflinera View Post
    My question is about the 29-bit CAN protocol.
    When the test equipment want to ask about the RPMs in mode 1, what frame is used? Is it correct the next frame?
    ID: 18DB33F1h Data: 02h 01h 0Ch Aah Aah Aah Aah Aah
    Looks fine.

    Quote Originally Posted by fflinera View Post
    On the other hand, what will be the response frame of the diagnosis unit? Is it correct the next frame?
    ID: 18DAF1xxh Data: 04h 41h 12h 70h 0Ch Aah Aah Aah
    Pretty close:
    ID: 18DAF1xxh Data: 04h 41h 0Ch 70h 0Ch Aah Aah Aah
    Note the PID is echoed as 0C, followed by the value 700Ch. Your example indicates 7,171 RPMs.

    Quote Originally Posted by fflinera View Post
    What usually takes xxh value in the ID of the response?
    You should assume that xxh can be anything and that it will be different from vehicle to vehicle. As you noticed on 11-bit networks there are 8 reserved pairs of addresses. On 29-bit networks there's more freedom. Since you're sending and receiving raw CAN frames it really doesn't matter (just filter on 18DAF1xx and allow anything in that byte).

    Using a J2534 device you'd want to know those addresses so you can setup ISO15765 flow control. The typical approach is to make an 0100 request, look at which ECU addresses respond, then setup ISO15765 flow control for each one.

    Quote Originally Posted by fflinera View Post
    What type of OBD protocol is used by VOLVO ? 11 or 29 bits?
    Not sure. For most software developers it doesn't matter -- the correct answer is to support both.

    Quote Originally Posted by fflinera View Post
    On the other hand, trucks or farm machinery that is manufactured using ECUs according standard J1939 usually have a diagnostic connector similar to the sport vehicles. Despite using the J1939, Can you connect a test equipment and try to make a test in the track in a similar way to you do in a sport vehicle?. Do they use the 29-bit protocol ?
    J1939 has a round connector and works completely differently. If you're plugged into a round J1939 connector then you cannot perform OBD-II diagnostics. If you're plugged into an OBD-II (J1962) connector then you're probably not dealing with J1939.

  3. #3
    Variable Bitrate
    Join Date
    Oct 2008
    Posts
    376
    Early Volvo's (around 2003 - 2004) use 29-bits Can with a baudrate of 250K.
    I think the latest Volvo's will use 500k, because 250k is only allowed under EOBD and not under OBD2.
    The xx in the reply ID usually follows the recommendations for ecu id's from other protocols. So, 10H - 17H for the engine, 18H - 1Fh for the gearbox, etc.

    I have tested (laboraty environment) with a 24 volt Iveco ecu, that used 29-bits Can at 250k.
    Wasn't interested in codes or data, just the protocol.

  4. #4
    Newbie
    Join Date
    Dec 2009
    Location
    spain
    Posts
    5
    Thank you joeyoravec and p2psmurf for your answers.
    Joeyoravec, I agree with you, the response must be
    ID:18DAF1xxh Data: 04h 41h 0Ch 70h 0Ch Aah Aah Aah
    with 0Ch instead of 12h (perhaps I was thinking in decimal)
    Nevertheless, the value for the RPMs is 0C70h = 3184d that according to OBD-II PIDs is 3184/4 = 796 RPMs (my car engine idling)
    The fourth data byte is less significative than the fifth.

    About J2534, I do not know very much. I have read something similar to the "0100 request" that you say in the
    canbushack web page (Scanning for diagnostic data - http://www.canbushack.com/blog/index.php?blog=5&paged=2.
    But, I must read it again to try to learn something more. Thank you for your answer, It had clarified a lot my doubts about 29-bit CAN-OBD.

    The question about VOLVOs was due to my attempt to use my ELM327-based OBD tester in a friend's VOLVO car.
    In my setup, I used a USB-CAN tool in parallel with my ELM327 to sniff frames. I read a lot of frames with 11-bit protocol.
    11-bit protocol was detected by Digimoto and ScanMAster software. I will try to make a new attempt using only 29-bit protocol. Perhaps in new VOLVOs
    you can use both profiles (29-bit & 11-bit).

    My question about 29-bit on trucks is due to the following:

    I am trying to learn something more about J1939. For that, I can connect my USB-CAN sniffer in a J1939 based coach from the manufacturer MAN.
    This coach has a J1932 OBD-II connector near the driver. I had also available the MAN test equipment.Sniffing, I had seen how the test equipment
    tried to ask to the vehicle using the following frames:

    ID:18DA3DF0h Data: 02h 10h 01h AAh AAh AAh AAh AAh
    ID:18DA3DF0h Data: 03h 22h F1h 81h AAh AAh AAh AAh
    ID:18DA27F0h Data: 02h 10h 01h AAh AAh AAh AAh AAh
    ID:18DA27F0h Data: 03h 22h F1h 81h AAh AAh AAh AAh
    ID:18DA00F0h Data: 02h 10h 01h AAh AAh AAh AAh AAh
    ID:18DA00F0h Data: 03h 22h F1h 81h AAh AAh AAh AAh
    ID:18DA10F0h Data: 02h 10h 01h AAh AAh AAh AAh AAh
    ID:18DA10F0h Data: 03h 22h F1h 81h AAh AAh AAh AAh
    ID:18DA27F0h Data: 02h 10h 01h AAh AAh AAh AAh AAh
    ID:18DA27F0h Data: 03h 22h F1h 81h AAh AAh AAh AAh

    In this case, the vehicle did not respond to any request. Someone of MAN told me later that CAN is not available in this connector, they only have available ISO-9141 in this connector.
    But, viewing these frames, I can obtain the following conclusions:
    1- The coach uses J1939, but they also use ISO15765 or is compatible, at least, the physical CAN id 18DAh
    2- F0h is the address of the MAN tester different to the usual external test equipment address (F1h usually)
    3- 3Dh, 27h, 00h and 10h are adresses of different nodes that the tester is looking for.

    My question is if this compatibility between J1939 and ISO15765 is usual in trucks and other agricolal equipment.

    On the other hand, the MAN tester has an adaptor between a round connector and a J1962 OBD-II connector.

    Apologize if I have used some wrong term or word during my explanation, but I am a newbie and I am trying to fix all that I know about CAN protocols in vehicles.

    Thank you again

  5. #5
    Variable Bitrate
    Join Date
    Oct 2008
    Posts
    376

Similar Threads

  1. Having doubts on my install, need HELP!
    By HiJackZX1 in forum Fabrication
    Replies: 23
    Last Post: 07-24-2008, 02:00 PM
  2. Cant instal - Centrafuse + Doubts
    By PORTUGAL in forum Centrafuse
    Replies: 3
    Last Post: 10-25-2007, 11:40 AM
  3. Which protocol is this?
    By aghazi in forum Engine Management, OBD-II, Engine Diagnostics, etc.
    Replies: 5
    Last Post: 12-16-2006, 10:34 AM
  4. OBD-II IOS protocol (BMW)
    By sstainba in forum Coders Corner
    Replies: 0
    Last Post: 03-16-2006, 07:00 PM
  5. motherboard grounding & psu doubts
    By RoyN in forum General Hardware Discussion
    Replies: 15
    Last Post: 02-25-2005, 02:26 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •