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Vehicle diagnostic port

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  • Vehicle diagnostic port

    This is a bit off topic, but I figured someone here might know. I was reading some of the FAQs on the AutoPC web site about how these stereo connects to the vehicles diagnostic port.

    Are the specs to this port freely available, or do you have to be an industry insider to be able interface to this port?

    Like the other poster mentioned, I want to be able to do a lot more than just hook my PC up to the stereo...

  • #2
    Sometimes I see articles in electronics hobyist magazines about auto electronics. As far as I can gather each manufacturer has different system and that they are proprietry. Unless someone has reverse engineered a system and made it public, I don't think you have much chance.



    • #3
      Many vehicles manufactured by the big 3 since the mid 90's have a serial bus which the engine, transmission, body controller and other items comunicate on. Ususally, there is access to this bus via an under-dash OBD-II connector.
      I am only familiar with the GM version of this (the systems used by each manufacturer are different), and to the best of my knowledge, the only sound-related item on this bus is vehicle speed, which is used for the "speed compensated volume" on the higher end radios.
      If anyone else is interested in working on the GM version of this vehicle serial bus, let me know. It would be a cool item to play with.
      K6-2 450 SBC, miniature case, dc power supply, 5gb laptop hdd


      • #4

        This company sells a sensor that hooks up to the computer via a serial connection. Their software is DOS but im sure someone could write something to get vehicle speed or any of the many other readings it gives out.
        MP3 Cavalier -
        MP3 Grand Prix -


        • #5
          Yes, it appears that this port really doesn't have anything to do with the stereo but rather allows the AutPC stereo to interface with the car itself an monitor things like speed, gas casumption, ignition status, door lock status, etc...

          Here's a sample of the AutoPC's header file for 3rd party developers:

          CLSID_VIOVEHICLE Returns information about the vehicle as a whole.
          CLSID_VIO_IOCTL Returns information about the API.
          CLSID_VIO_IGNITION_SWITCH Returns the status of the ignition switch.
          CLSID_VIO_HEADLIGHTS Returns the status of the headlight switch.
          CLSID_VIO_PARKING_BRAKE Returns the status of the parking brake.
          CLSID_VIO_VEHICLE_SPEED Returns the current vehicle speed.
          CLSID_VIO_ENGINE_RPM Returns the current crankshaft rotation rate.


          • #6
            I myself have wondered about the little connector port in my car. I researched it and it is called the OBDII interface. All cars '96 and up are required by law to have this within 3 feet of the driver. Although I haven't seen actual specs of the port, I found someone who sells software and a Connector --> Serial cable for any ole computer. I would have bought it but the hefty price ($600 US) completely changed my mind.


            • #7
              Here is a little more information. I found another company that sells adapters to go from OBDII to RS232.. however, they dont sell the software and you would have to develop your own (they help you with technical data and pinouts). is the URL to the companies website. Ive been in contact with one of their people and they very quickly answer your questions via Email. The price for the Gm adapter is $72.00 USD which isnt too bad. Something to look into to get speed displays etc.
              MP3 Cavalier -
              MP3 Grand Prix -


              • #8
                Check out this page:

                It hooks up to your cars port and collects a lot of information, and displays it for you. You can also control some of the engine's settings with it. It would be awesome if it was possible to hook into into the transmission's computer and tell it when to shift, and have one of those electronic type transmissions. Just an idea though, if i had an automatic id research it more. Probably impossible though.