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Thread: OBD-II Permanently Connected

  1. #1
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    OBD-II Permanently Connected

    I am not sure if this has been addressed in the past or not, I did not see anything directly discussing this from searches I did. How safe is it to leave an OBD-II reader permanently connected and constantly reading/polling data from the ECU? I have heard that initializing the OBD-II connection puts the engine/ECU in a somewhat "special" mode which makes me wonder if leaving it consantly running is not good for the car. Let me know if any of you have any information on this.

  2. #2
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    Obd-ii

    I am also interested in this... it's my understanding the ECU must be taxed somehow by the OBD-II link constantly polling it for data...

    Is there anyone out there that can provide any info on this?

  3. #3
    FLAC cproaudio's Avatar
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    Mines been connected since Nov 2002. havent notice any changes in performance, gas mileage. Check engine never came on due to OB-II plug. It only collects data when you're running the software.
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  4. #4
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    cproaudio, how much have you had the software running and collecting data? also, what kind of car and year do you have? most practical applications of OBD-II in a car computer setup would involve polling pretty often. and just for confirmation, simply having the obd-ii reader connected to the car has *no* effect on the ECU until it is initialized and polling, correct? Thanks for the help,


    -Blake

  5. #5
    FLAC cproaudio's Avatar
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    I have a 97 Toyota Tacoma. For my setup, the obd-ii has been connected since Nov of 2002. I use the obd-ii software for digital dash at least once a week. Everytime I used it is for at least an hour. Most of the time I use it on long trips 100+ miles per trip. So far I have not experience any effects on the ECU. It's been almost a year now. It only initialize the scanner when the software is running.
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  6. #6
    Maximum Bitrate brrman's Avatar
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    I have driven my Audi running OBDII diagnostic software for extended periods of time with no side effects.

  7. #7
    Maximum Bitrate wi77iam's Avatar
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    Quote Originally Posted by jasonsp6
    I am also interested in this... it's my understanding the ECU must be taxed somehow by the OBD-II link constantly polling it for data...

    Is there anyone out there that can provide any info on this?
    A data logger or computer using an OBDII connector is not a polling device, i.e. it does not suck data out of your ECU. Data is just available at the connector for reading at the rate that the ECU outputs.

    There should be no problem having a permanent connection.

  8. #8
    Maximum Bitrate gork's Avatar
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    It's worth noting that some ODB II hardware are actually read-only .. ie they dont even have the ability to write to the port. From the standpoint of an auto technician, it would not make much sense for the car to change the way it performs when the connector is plugged in since it would hinder the ability of the tech to diagnose a problem.

    Notwithstanding, many cars do have special modes that hamper performance. I Know my car has an "Emissions Dyno Mode" where it will not rev above 6K RPM, and that mode is probably accessible via the diagnostic connector, but I imagine that you have to send some special commands down the wire to get a car to switch to some other diagnostic mode.

  9. #9
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    data from the OBD-II connector does have to be "requested" from the ECU (i know this as a programmer....a few bits are sent, and then a few response bits are returned)....but overall it does sound like from these replies that it should be fine to leave it permanantly connected and running. i agree that it would not make sense to have the engine go in to a different mode when you are trying to diagnose information about what it is doing. anyways, thanks for the help, i believe my question has been answered now.

    -blake

  10. #10
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    if it was readonly how would they use it to clear check engine lights and such?

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