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J1850 PWM specs

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  • J1850 PWM specs

    I am trying to build my own code reader using a PIC interfaced to a laptop for J1850 PWM to use with a Ford but having a hard time finding information about the protocol. Are there any resources on the web that explain it? I have various links bookmarked that explain the general workings of it but nothing really detailed.

    Yes, I realize that I have to pay for the SAE documents but I am a poor college student doing this for a school project so I can't afford it. Any help is appreciated.

  • #2
    I think I figured out most of the protocol but have a couple of questions still. Is the CRC byte always 0x0a?

    I am going by examples here,


    • #3
      This may help:


      • #4
        Some timing information here:


        • #5
          Thanks for the links. I was able to get a hold of the actual SAE documentation which I found rather confusing.

          Never the less I am now able to receive data from the ECM. My question now is about IFR. I think I am missing something.

          Here is what's happening right now. I am sending

          SOF 0x61 0x6A 0xF1 0x01 0x00 0x0A EOF

          The reply I get back is

          SOF 0x41 0x6B 0x10 and either nothing else or a few 0x00 bytes

          What am I missing? Am I suppose to send something back after I get 0x10 byte?


          • #6
            Looks like I am doing something incorrectly. The response that I receive back is on the line constantly, regardless if I send anything to the ECU or not.

            I guess my question would be, at what point should I be requesting data?