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Could you instruct a car thru the OBD port to open the trunk even if the car was turned off? Can you turn the accessories on from the port then open the trunk?

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    I suspect this is highly dependent on the make, model and year of the car @Bernie. Can you edit your question with these details?
    – GdD
    May 30, 2018 at 13:53
  • So here is what I am thinking: If OnStar can pop the trunk on GM cars for Amazon, what if an ODB device could do the same universally?
    – Bernie
    May 30, 2018 at 15:30
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    On Star has direct access to the body control module. which does not turn off with the key.
    – Moab
    May 30, 2018 at 16:02

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According to this response, when the ignition key is removed from the car it's usually not possible to communicate with the car via the OBD port so assuming by "turned off" you mean the ignition key removed, I'd say in most cases it is not possible.

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I've seen someone with a diagnostic tool (sort of like the one your mechanic uses, that has its own power supply) tell a car to open its trunk via the ODBII port. The customer had locked their keys in the trunk and a roadside tech could open the door, but the security disabled the trunk release.

Being that roadside tech, I would dearly love to find such a tool. Currently I have to open the car manually, then disassemble the door (on some cars) to access the lock and 'unlock' the car by manipulating the lock manually. A PITA, to say the least.

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  • If it was made easy, then the car could be stolen easily... Do you want your car stolen?
    – Solar Mike
    May 6, 2021 at 5:22
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The whole idea of the On Board Diagnostics port is to provide vehicle diagnostic information. It is read-only, except for specific log entries and specific fault codes that can be reset. It is not meant as a control interface for your car.

Also see Can i control the brakes of a car by the OBD II Interface?

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    Not entirely true for all cases. The Carly tool mycarly.com/product/bmw-app for BMW can reprogram many operations of the vehicle. Of course what's available in the BMW may not be pure "OBD."
    – mike65535
    May 30, 2018 at 15:59
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    Actually you can flash the ecm via the obd2 port, and likely a lot of other things by accessing pid's. Dealerships do it all the time solving problems.
    – Moab
    May 30, 2018 at 16:00
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    And, every time you clear codes, the reader has to communicate with the ECU to do it ... that's not one way comms either.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 30, 2018 at 16:27
  • @Moab that often is done via another connector directly on the CAN bus instead of through the OBD port. But again, depends on manufacturer.
    – MadMarky
    May 30, 2018 at 18:51
  • @Pᴀᴜʟsᴛᴇʀ2 just like i mentioned in my post, only some (not all) log entries and fault codes can be reset. Thats it.
    – MadMarky
    May 30, 2018 at 18:51

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