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J1979 CAN header question

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  • J1979 CAN header question

    I have interfaced to my older Ford vehicle using J1850 PWM. Now I am working on CAN in a newer vehicle. I own a copy of J1979 but am a little confused about the header for CAN PID value requests.

    Here is a sample request for RPM in J1850 PWM (in hex of course):

    request:
    61 6A F1 01 0C crc
    response:
    41 6b nn 0C aa bb crc
    where nn=ECU address, aa bb = DATA A and DATA B

    Can anyone give me this same example in CAN?

    Thanks,
    Steve

  • #2
    In PWM 61 6A F1 is the header.
    For Can the header will be setup by the can-chip. All you do is supply a address where to send it, either 11-bit or 29-bit.
    The data is the same as for any other protocol: 01 0C.
    See page 22 of you manual.

    Comment


    • #3
      for 11bit its 0x7DF for the functional addressing or (typically)0x7E0 for the physical address of the Engine computer. The response from the Engine computer is typically 0x7E8.

      What tool are you using to do the requesting?

      Comment


      • #4
        I am using a Multiplex Engineering T21 card attached to my embedded microcontroller. In the future I will use the CAN module on my embedded micro.

        Steve

        Comment


        • #5
          With 11-bits can there's no guarantee that 0x7e0 is the engine.
          Could be anyone from 0x7e0 through 0x7e7.

          Comment


          • #6
            Originally posted by p2psmurf View Post
            With 11-bits can there's no guarantee that 0x7e0 is the engine.
            Could be anyone from 0x7e0 through 0x7e7.

            That's why I said typically. It has been for every car in my experience, but I know there is no guarantee.

            Comment


            • #7
              I have done more research and study on this issue. See if this looks correct:

              The CAN message for RPM:

              7DF 02 01 0C

              7DF = The 11 bit CAN ID
              02 = 2 data bytes used out of the possible 7 CAN data bytes
              01 = Service 01
              0C = RPM PID

              What do y'all think?

              Steve

              Comment


              • #8
                Looks good to me. Depending on how your hardware you may not need to put the 02.

                Comment


                • #9
                  Originally posted by EngineerSteve View Post
                  I have done more research and study on this issue. See if this looks correct:

                  The CAN message for RPM:

                  7DF 02 01 0C

                  7DF = The 11 bit CAN ID
                  02 = 2 data bytes used out of the possible 7 CAN data bytes
                  01 = Service 01
                  0C = RPM PID

                  What do y'all think?

                  Steve
                  Here's a sample of actual communication b/w an ElmScan 5 scan tool, and ECU Sim (as reported by ECU Sim):

                  Code:
                  7DF 02 01 00
                  7E8 06 41 00 88 19 10 10
                  7DF 02 01 1C
                  7E8 03 41 1C 06
                  7DF 02 01 01
                  7E8 06 41 01 83 0F EF 80
                  7DF 02 01 0C
                  7E8 04 41 0C B6 DA
                  Is this a commercial project?

                  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.
                  Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

                  You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

                  Comment


                  • #10
                    By the way, CAN lets you increase the throughput by combining several PID requests into one, like this:

                    01 00 01 05 0C 0D

                    Vitaliy
                    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
                    Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

                    You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

                    Comment


                    • #11
                      Vitaliy:

                      Thanks for the good reply. I begin to see what is going on.

                      The project is potentially commercial. I have an interest in this stuff and my company could possibly develop a vehicle based product that could use the data from OBDII.

                      Personnaly I would like to learn communications with vehicle ECU's, I think it is a career enhancer.

                      Steve

                      Comment


                      • #12
                        Originally posted by EngineerSteve View Post
                        Vitaliy:

                        Thanks for the good reply. I begin to see what is going on.

                        The project is potentially commercial. I have an interest in this stuff and my company could possibly develop a vehicle based product that could use the data from OBDII.

                        Personnaly I would like to learn communications with vehicle ECU's, I think it is a career enhancer.

                        Steve
                        My company (ScanTool.net) helped a number of companies integrate OBDII into their products. We also sell OBD cables (through obd2cables.com), connectors, ECU simulators (ecusims.com), OBD chips, etc., as well as providing consulting services.

                        If you would like to discuss this off-line, best way to reach me is via email, vitaliy(A)scantool.net

                        </end shameless plug>

                        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.
                        Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

                        You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

                        Comment


                        • #13
                          I'll shamelessly plug them too. They really know their stuff and can help a lot.

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