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Thread: Is the OBDII port powered up with the ignition off?

  1. 24th November 2015, 05:50 PM #1
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    Is the OBDII port powered up with the ignition off?

    Hi,

    I was just wondering if the OBDII port is powered up with the ignition off?

    The disco battery was completely flat after being left standing for about a month and I was wondering if the wifi OBDII reader that I have plugged into the port was the culprit.

    Thanks
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  2. 24th November 2015, 05:53 PM #2
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    It shouldn't...
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  3. 24th November 2015, 07:40 PM #3
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    I've read posts saying the opposite...

    ten seconds with a multimeter would end this
    "How long since you've visited The Good Oil?"

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  4. 24th November 2015, 07:51 PM #4
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    Quote Originally Posted by Pedro_The_Swift View Post
    I've read posts saying the opposite...

    ten seconds with a multimeter would end this
    Unfortunately I'm at work in Nigeria and I'm not game to try explaining how to use a multi meter to the Mrs.

    I've just got off the phone trying to explain what the OBDII box looks like and asking her to unplug it just in case. That was hard enough.................

    She did change the battery for me though
    Last edited by WAWoody; 24th November 2015 at 07:56 PM. Reason: Spelling
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  5. 24th November 2015, 08:03 PM #5
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    Quote Originally Posted by Pedro_The_Swift View Post
    I've read posts saying the opposite...
    A lot of googling and it would seem that you are right. Power to the port even with the ignition off.

    Cheers
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  6. 24th November 2015, 08:20 PM #6
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    The power usage theory is the reader keeps waking up the cars systems,,

    I must admit to disconnecting mine after my recent flat battery episode,,,
    "How long since you've visited The Good Oil?"

    '93 V8 Rossi
    '97 to '07. sold.
    '01 V8 D2
    '06 to 10. written off.
    '03 4.6 V8 HSE D2a with Tornado ECM
    '10 to '21
    '16.5 RRS SDV8
    '21 to Infinity and Beyond!

    1988 Isuzu Bus. V10 15L NA Diesel
    Home is where you park it..

    [IMG][/IMG]
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  7. 24th November 2015, 08:28 PM #7
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    Yes there is power with ignition turned off. Standard process with the Hawkeye reader is to plug it in with the ignition turned off and only turning it (the ignition) on when requested by the menu displays.
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  8. 24th November 2015, 08:30 PM #8
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    Thinking about it now, the iPhone was picking up the wifi from the OBDII box when the ignition was off, so it must have still had power and been transmitting a wifi signal of some description.

    Should have twigged then really.
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  9. 24th November 2015, 08:52 PM #9
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    Hmmm why is it that engine management systems hand controllers don't have power to them until the key is on? (Wolf, Haltech, etc).
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  10. 24th November 2015, 09:11 PM #10
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    there is and there isnt power to the obdII port...

    while the system is active (ignition on) a device can request a shut down delay across the port for various vehicle subsystems (security, radio, door locks, some engine monitoring, prox sensors to name a few) so when you turn the ignition off this stuff will stay turned on until whatever is keeping the "network" active turns off or tells everything to shut down.

    IF you plug something in while the system is inactive (ignition off) then it wont activate until something else wakes up the system for it or you turn the ignition on.

    IF you have something that is interrogating say the engine ECU then at a minimum the ECU+the device that controls the onboard network should all remain active. while the network is up and running at regular intervals everything else thats on the network will be at certain time intervals broadcasting a "there is still power on the network, do you want me to wake up and do something yet?"
    Dave

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