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Thread: OBD2 works with the car off not on?

  1. #1
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    OBD2 works with the car off not on?

    Righto, I purchased a cheapy OBD2 to USB (via serial to USB converter included) to display vehicle sensor data, but have run into a problem. Vehicle is a Hyundai Sonata 1999.

    I can read the vehicle data (RPM, throttle position, temps blah blah) when the ignition is ON but car NOT started. Data flows like Niagara Falls. However as soon as I start the car, data flow disappears :-( Even if I unplug and re-plug, nothing. Turn the car off and back into ignition on without starting it and the data comes through again.

    Anyone played with one of these devices before and could have any ideas? I've tried a few settings in the Serial to USB driver but there aren't many to change.

    Software I've used I can't recall the name but I've also used Curiosity's own little reader with the same result.

  2. #2
    What can I say? I like serial. Curiosity's Avatar
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    I've never seen that happen. Does it have any LEDs on it? Do they stay on when the car is running? Maybe we should use the scantool software (or what it came with) and get info first, like the protocol it detects and what happen when starting. It should report an error, but it might just be timeout or something vague.

  3. #3
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    Yes it has Power / OBD tx rx / USB tx rx. The Power light always stays on, it never looses powers.

    As soon as you crank the car any software reading the data just comes up interface not found If I unplug and re-plug any software acts like the interface/car isn't connected.

  4. #4
    What can I say? I like serial. Curiosity's Avatar
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    Oh that sounds bad. The power connection doesn't change when you run the car, but the voltage increases. First thought would be the voltage regulator on the alternator causing the volts to get too high or making it noisy or the OBD-II device isn't very good at regulating. That's all I can think of that would be different. Anyone else have ideas?

  5. #5
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    Well seli-good news, I tried the same device on a new'ish Hyundai i30, and it read the vehicle data with the car running flawlessly.

    So it still seems to be a problem with my car when its running?

  6. #6
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    Australian cars do not have to comply with OBD2 (or Australian version of it) in 1999.
    I think it was first introduced in 2005?
    So, it's probably a problem in the cars software.

  7. #7
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    Yes that is true, its just really strange how I can get all the data perfectly fine with the ignition on but not running

    EDIT: Oh and something I noticed, if the car is running and I unplug and re-plug the USB interface it sometimes comes up USB device not detected. Which is why I thought the device was just crap but yeah like I said no issue/error with the i30.

  8. #8
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    I've seen this on many ecu's on older cars. Usually it's the ABS that stops communicating when the engine is started. Very, very annoying and almost impossible to find problems as the codes are cleared when the ignition is cycled off/on.

  9. #9
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    Hrmm well my car doesn't have ABS

  10. #10
    Raw Wave
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    It could be a good issue for SiliconChip - see their Feb10 issue (obd2 interface etc).

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