Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: J1979 CAN header question

  1. #1
    Newbie
    Join Date
    May 2009
    Location
    Irving, TX
    Posts
    6

    Exclamation 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. #2
    Variable Bitrate
    Join Date
    Oct 2008
    Posts
    376
    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.

  3. #3
    Low Bitrate
    Join Date
    Sep 2008
    Posts
    99
    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?

  4. #4
    Newbie
    Join Date
    May 2009
    Location
    Irving, TX
    Posts
    6
    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

  5. #5
    Variable Bitrate
    Join Date
    Oct 2008
    Posts
    376
    With 11-bits can there's no guarantee that 0x7e0 is the engine.
    Could be anyone from 0x7e0 through 0x7e7.

  6. #6
    Low Bitrate
    Join Date
    Sep 2008
    Posts
    99
    Quote 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.

  7. #7
    Newbie
    Join Date
    May 2009
    Location
    Irving, TX
    Posts
    6
    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

  8. #8
    Low Bitrate
    Join Date
    Sep 2008
    Posts
    99
    Looks good to me. Depending on how your hardware you may not need to put the 02.

  9. #9
    VENDOR - ScanTool Vitaliy's Avatar
    Join Date
    Dec 2006
    Location
    Phoenix, AZ
    Posts
    624
    Quote 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.

  10. #10
    VENDOR - ScanTool Vitaliy's Avatar
    Join Date
    Dec 2006
    Location
    Phoenix, AZ
    Posts
    624
    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.

Page 1 of 2 12 LastLast

Similar Threads

  1. Question about CF 1.7 and the global 'header'
    By justintime in forum Centrafuse
    Replies: 3
    Last Post: 06-27-2006, 08:15 PM
  2. Replies: 2
    Last Post: 05-02-2006, 05:15 PM
  3. Forum Etiquette
    By Enforcer in forum Newbie
    Replies: 5
    Last Post: 01-09-2006, 05:58 PM
  4. Paint And Polish Question
    By gboy in forum Fabrication
    Replies: 8
    Last Post: 08-13-2005, 07:22 PM
  5. FM Card Question....
    By Superbike1k in forum Car Audio
    Replies: 1
    Last Post: 05-16-2005, 09:03 AM

Tags for this Thread

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
  •