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OBD2 works with the car off not on?

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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
    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.

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    • #3
      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.

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      • #4
        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?

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        • #5
          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?

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          • #6
            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.

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            • #7
              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.

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              • #8
                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.

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

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

                    Comment


                    • #11
                      The ELM device's USB interface is disconnecting from the PC. That has nothing to do with OBD-II compliance or anything. Have you tried plugging the OBD-II port in after the car is running? I'm still thinking it's power related. If that works, then the voltage drop durring crank locks it up.

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                      • #12
                        There's a simple solution I have for you... sell the Sonata and get the i30

                        Other than that I've got nothing to add.
                        03 Hyundai Elantra GT {Worklog}
                        HP TC4400; 250GB SATA, WiFi, BT, 12.1" touch
                        RideRunner; w/ mobilephone.net, OBDMPG, mediaart, RRMedia, DFXVoice and more...
                        cmdRR tall skin creator

                        86 Pontiac Fiero SE 2m6
                        possible carpc install

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                        • #13
                          OBDII Disconnect

                          Just a few things:
                          Is the laptop powered from the car's electrical system? If so, you may have a ground loop that can have issues for USB adapters. Run the laptop on battery or powered from a separate source.
                          I use AutoEnginuity and they posted this as an issue with their USB scan tool.
                          Good luck,
                          DNR

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                          • #14
                            Yah, wait until the car is started before plugging in the OBDII cable and run laptop off of battery power, then report back.
                            Originally posted by ghettocruzer
                            I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                            Want to:
                            -Find out about the new iBug iPad install?
                            -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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                            • #15
                              Originally posted by Curiosity View Post
                              The ELM device's USB interface is disconnecting from the PC. That has nothing to do with OBD-II compliance or anything. Have you tried plugging the OBD-II port in after the car is running? I'm still thinking it's power related. If that works, then the voltage drop durring crank locks it up.
                              Yeah I gave that a go already as per my previous post, started the car and then plugged it in and it often comes up USB device not detected:

                              Originally posted by yorky View Post
                              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.
                              Originally posted by dnr250 View Post
                              Just a few things:
                              Is the laptop powered from the car's electrical system? If so, you may have a ground loop that can have issues for USB adapters. Run the laptop on battery or powered from a separate source.
                              I use AutoEnginuity and they posted this as an issue with their USB scan tool.
                              Good luck,
                              DNR
                              Yep I tried two different laptops, firstly one running off laptop battery, then one running off the car, same result on both

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