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  • CAN Bus Interfacing

    I would like to interface with my car's can bus so that I can decode its packets to can access to the car's systems and radio via my computer. Can i just plug my CAN module into the OBD-II port since I have noticed that the OBD-II had the can high and low connections or is there specific port on the car for interfacing directly with the CAN Bus.

  • #2
    Yes you can plug directly into the obdii port but keep in mind on many vehicles there are two seperate buses:
    A low speed bus for radio, entertainment, climate control, etc.
    And a high speed bus for everything else

    If thats the case with your car you will only be able to access the high speed bus through the obdii port.
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    • #3
      Opel and GM uses 3 different can-buses. High-speed (powertrain) and mid-speed bus, which are 2-wire can and the low-speed bus which is a single wire can. Rumor has it that the new Insignia has 4 can-buses.

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      • #4
        Ya its gonna depend on what car you have. I have a Chrysler 300.

        In Chrysler Jeep and Dodges there are 3 can busses and you can not access the Interior Comfort CAN Bus ( Radio, Climate Control, Car Audio system, Dash cluster, EVIC, etc.. ) from the OBDii port. You can tap into this can bus at the radio wire harness though.

        So it'll depend on the car you have
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        • #5
          Yea I have a 2008 Hyundai Elantra just trying to actually integrate my EE senior design project with my car now as a hobby. Currently I have the software written to work with OBD-II commands. So basically from what all of you have said is that to obtain vehicle metrics I can just tap into the OBD port with any can device. To control anything happening inside the car's cabin I would have to splice into the radio's wiring harness.

          For the vehicle's that have three bus lines, I see from above that one is high speed for vehicle information there is a mid speed and a low speed. Is the low speed bus for the entertainment system and what is the medium speed bus used for.

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          • #6
            Use of the different buses depends on the vehicle manufacturer.
            High-speed bus is for Engine, Gearbox, ABS en EOBD/OBD2 diagnostic messages.
            Mid-speed bus is usually Airbag, Airco.
            Low-speed bus is usually entertainment.

            Your software that works with OBD2 commands is useless when you want to control the car. You need to reverse engineer each bus and find out what you have to send and what you receive.
            Is your hardware capable of both standards? Because single-wire can uses a different signal?

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            • #7
              Originally posted by Talguy View Post
              Yea I have a 2008 Hyundai Elantra just trying to actually integrate my EE senior design project with my car now as a hobby. Currently I have the software written to work with OBD-II commands. So basically from what all of you have said is that to obtain vehicle metrics I can just tap into the OBD port with any can device. To control anything happening inside the car's cabin I would have to splice into the radio's wiring harness.

              For the vehicle's that have three bus lines, I see from above that one is high speed for vehicle information there is a mid speed and a low speed. Is the low speed bus for the entertainment system and what is the medium speed bus used for.
              An Elantra may be entirely different. For example, on VW/Audi cars you can get access to everything via the OBD port.
              -James
              Car: 2004 GTI VR6 24v Turbo 2.8L, GT35R, 630cc, Unitronic, Bosch 044, etc, etc..
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              • #8
                I really haven't looked into the elantra's can bus yet. just trying to figure out the overall concept of the bus and what I should look for and if there are any standard packets that flow over the bus that is standard for all cars. As for my OBD software I just a custom C++ class that worked with an elm327. Right now I picked up a pic32 7xx family that has a dual can bus controller built onto the chip. I plan to build my own can bus interface using this chip and connect it to my computer via USB.

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                • #9
                  Yeah I would go ahead and do that and plug it in and see what you can sniff off the bus.
                  -James
                  Car: 2004 GTI VR6 24v Turbo 2.8L, GT35R, 630cc, Unitronic, Bosch 044, etc, etc..
                  Main PC:i7 [email protected], 6GB DDR3, MSI X-58 Pro-E, Win 7 x64 RTM, Scythe Mugen2, 128GB G.Skill Falcon, 2x ATI4850 512MB Crossfire, Auzentech X-Fi Forte, Grado Labs SR-80

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