I am buying an OBD2 Head Up Display. It has a screen where it shows readings etc. Manufacturer claims the item turns off when the engine is off too, and this is true from the videos I have watched. It turns off along with the ignition.

However, does that mean it uses absolutely ZERO battery when the engine is off? Or does it still use a tiny bit?

I am afraid of waking up to a dead battery one day, and if it uses 'minimal power', I am not sure how minimal it actual is if that makes sense.

  • 1
    The answer depends upon the design of HU Display. Ask the manufacturer, 'tho it's possible or even likely that the manufacturer will not reveal this information. The only foolproof method of knowing is to have the device in-hand, connect it to a car, and monitor the device's power use when the ignition is off. It may be that while the device does use power when the device is turned off, the power consumption is so small (like a small digital clock for instance) that a car with a good and fully-charged battery can sit happily for months and restart briskly after a lengthy no-run period. Oct 8, 2022 at 16:43
  • Sorry if that is stupid, I am not much of a car guy but..how do I do that? How do I check power consumption when ignition is off to figure out whether it draws power or not? Do I go to a car shop?
    – Antonis
    Oct 8, 2022 at 16:46
  • This isn't a discussion board, it is instead a question-and-answer site. You can read the Help pages to learn more about how the site works. You've now asked a different question about "how to measure." Please use the "Ask Question" button at the top, and ask this as a new and separate question. Oct 8, 2022 at 16:52

1 Answer 1


If the power lead is attached to a switched on power source, there will be zero power consumption when the vehicle is turned off. A "switched on" power source is only active when the ignition is in the on or accessory position. Your HUD may or may not specify which power source to tie into. If the HUD draws its power directly from the Data Link Connector (DLC) where you get your OBDII connection at, then it has the possibility of pulling energy at all times, as the power source there is an always on source. If it does attach to the DLC, your best option is to pull this plug when the vehicle is not in use.

  • If this HUD connects to the OBD II port, pin 16 is hot at all times. 12v isn't switched off with the ign key. Some vehicles switch off the auxiliary power port(s) (aka cigarette lighter) with the ign key while older vehicles have their aux power port hot/live 12v at all times.
    – F Dryer
    Oct 8, 2022 at 19:37
  • It's a Toyota Aygo 2007. Well manufacturer claims it goes in sleep mode when ignition is off (and it does turn off when doing so), but I am not sure if it still draws power.
    – Antonis
    Oct 8, 2022 at 20:47

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