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Thread: How to begin OBD development?

  1. #11
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    So I am new to this as well... and I would like to know how it is possible to damage your car through OBD-II
    Is this a sarcastic question? In my unterstanding it is possible to send bytes to the controller which cause him to do a little bit more (perhaps reseting the service counter is one of the harmless actions), then sending back some simple status information. Isnt it this way?

  2. #12
    Variable Bitrate NeonDev's Avatar
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    I don't know thats why i'm asking... I just wouldn't think you could jack up your car with a diagnostic tool, but maybe you have a looser definition of harming your car...

    What is the worst thing that you can do to your car over OBD-II? I'm not really worried about resetting flags or anything...
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  3. #13
    Vendor - Qube colin's Avatar
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    Last time I checked, through standard OBD-II, the worst you can do is reset your MIL indicator -- which has it's side effects.

  4. #14
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    Quote Originally Posted by Mork0075 View Post
    Thanks a lot for your reply My concern is, that i'am doing something wrong, sending wrong bytes through the channel, which causes a damage. I've done some socket programming in Java, which is really close to what you've described (sending some bytes, waiting for the answer, adjusting the program). But writing your own test environement makes a lot of assumptions, which are perhaps wrong. So a pre build car emulator would give me the confidence, to not damage my car.
    I wouldn't worry about damaging the car. If you send the wrong series of bytes, the car is most likely to just ignore the data. Especially if you stick to just the read side of the protocol - where you send packets that mean "what is the value in register X?" with a response from car like "register X contains value Y." If you just implement that stuff you're very unlikely to cause any trouble. When you're confident that you have that stuff working, and working well, then ask yourself if you're ready to tackle writes. If you are, you are. If you aren't, then find some more cool stuff to do with reads. There's plenty of opportunity there.

    Frankly I wouldn't bother even trying to do writes. Mostly the software I use just reads data to display it or log it, and that's enough for me. I do use one piece of software to write (for tuning), and it makes me nervous every time I run it.

  5. #15
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    Can please someone provide us with sample code?

    then ask yourself if you're ready to tackle writes.
    How does a write look like? Reading from a register means also writing some bytes to the bus.

  6. #16
    Vendor - Qube colin's Avatar
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    He means writing to the ECU, changing things...

    most OBD stuff you use is just reading information like sensors, you can also tell the computer to change things about how your car runs (tuning...)

  7. #17
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    Yes, I meant writing to the ECU to change the tune, the state of the trouble codes, etc.

  8. #18
    Maximum Bitrate galvitron's Avatar
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    So we now know what commands to send (thanks all!)

    Now we need to know what baudrate, stopbits, parity, etc.?? to open the ComPort with...
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  9. #19
    Vendor - Qube colin's Avatar
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    Depends on what tool you use, each is different.

  10. #20
    North of the land of Hey Huns
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    Most of the ELM based tools use 96008N1 by default, you can switch to a higher baud rate but unless you are using CAN there isnt much purpose to it that I can find.

    I could provide some c++ code if it would help anyone, but I don't know if there are many here who develop in c++. I also wrote a c# emulator using a virtual-com port loopback, so you could connect your program to this program and test request/replies, but that requires a bit more setup.

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