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  • OBD n00b, any info?

    hi all,

    i am going to start working with the OBD1 protocol that my car computer spits out, but i cant seem to find anything on the actual data that is sent and received.

    its a nissan, and i will be reading it via serial directly, and want to create some custom digital gauges for my car that will come up on the computer screen, MPH, RPM etc,

    i know how to write programs, i know about electronics, and i know about serial, but surely if OBD is a standard then there should be a list of commands and expected data somewhere?

    can anyone help?

    thanks loads

  • #2
    OBD1 only requires manufacturers to produce a list with the fault codes in a car, not the communication protocol.
    OBD2 is another story, that uses defined protocols and data. See: http://en.wikipedia.org/wiki/OBD-II_PIDs

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    • #3
      Originally posted by p2psmurf View Post
      OBD1 only requires manufacturers to produce a list with the fault codes in a car, not the communication protocol.
      OBD2 is another story, that uses defined protocols and data. See: http://en.wikipedia.org/wiki/OBD-II_PIDs
      thanks very much for that, that is interesting, so is there anywhere where i can get manufacture specific details? also i am not really interested in the fault codes as i just want the gauges like MPH and RPM, is that a standard?

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      • #4
        Pretty sure those gauges are read off the transmission in a mechanical manner. OBD is very limiting in that regard. If you really wanted that stuff, you may be forced into purchasing a standalone that can output to OBD-II. Don't quote me on that though, but I have a feeling it won't work.

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        • #5
          i seem to remember a friend of mine showing me his consult cable working in his nissan, i think it was ODB1 and it seemed to have all the gauges working, so i suppose even though the readings might be mechanical for the speedo etc, they might still have some electronic signal sent to the ECU.

          i know my speedo is mechanical but it also has a reed switch on the back of the dial to count the number of rotations which i assume is for the ECU

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          • #6
            Eh, my guess is that really depends on the car. OBD-1's last year was 95 I believe, but some manufacturers may have started earlier.

            Also, that connection you saw may have been electrical for lighting in the cluster.

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            • #7
              Originally posted by neverrain View Post
              Eh, my guess is that really depends on the car. OBD-1's last year was 95 I believe, but some manufacturers may have started earlier.

              Also, that connection you saw may have been electrical for lighting in the cluster.
              thats strange, my car is a 97, and it seems to have the OBD1 socket, i will have to double check that it is actually ODB1 but as far as i know it is OBD1

              the reed switch on the back of the cluster is definitely for reading MPH, as i can get a pulse from it which increases with the speed of the car. i was originally going to have a relay board that read the gauge cluster directly, but now i want to get rid of the gauges so i need a signal from the ECU

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              • #8
                If you live outside the USA and Canada, there's nothing strange about it.
                OBD2 is ONLY used in the USA and Canada. Other regions in the world (Europe, Japan) may have similar rules, but they start a lot later (2001).

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                • #9
                  Originally posted by p2psmurf View Post
                  If you live outside the USA and Canada, there's nothing strange about it.
                  OBD2 is ONLY used in the USA and Canada. Other regions in the world (Europe, Japan) may have similar rules, but they start a lot later (2001).
                  that makes a lot more sense, my car is a Japanese import, and from what i can find out, Nissan Japan didn't use OBD2 until 2000

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