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Obd2 only works with engine running?

So i noticed the obd2 on my 2004 gmc sierra has power, but the scanner won't connect to it with the ignition on. But with the engine running, it connects just fine with no trouble codes. Why is this?

4 Answers

Relevance
  • 8 months ago

    Because it is designed to read the active codes which are generated when the engine is running.

  • Andy C
    Lv 7
    8 months ago

    No.  On, not running. 

  • Anonymous
    8 months ago

    It is probably a cheapo scanner.  Get a decent one.  As they always say, you get what you pay for.  If it is not a cheapo scanner, it is broken.  Do not overthink it.

  • 8 months ago

    It's usually a POS after market code reader. Go to Advance Auto or Auto Zone and try their code reader to see what happens.

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