Obd Port And Readers - Power On/off

February 3, 2012

Having read on here and other places about Scangauges I am tempted to get one, but it is a bit of outlay. So, having seen some other stuff, I decided to take a cheaper option as a first step and bought a bluetooth reader (ELM327) to work with my Android phone using Torque.

I've only had a quick play with it, without starting the engine as my Aygo is hiding in the garage from the cold, and I have had it connected and reading intake temp, etc, with the ignition on, so that is fine.

What surprised me is that the ELM is still powered (red LED is lit) when the ignition is off. As the OBD is officially a diagnostic port this isn't unreasonable, but I've never seen it mentioned in the info I've read. Is it a Toyota (or even Aygo) thing?

However, it raises a number of issues:

Power drain if its left in place all the time?

Will the ELM itself survive being on 24/7?

Is there any 'security' risk leaving an active bluetooth device in an unattended vehicle? (I'd hope the ECU itself is powered off, so there wouldn't be, but ..... ?)

If I plug/unplug it every day will this eventually damage the (physical) connector? Quite likely!

It also makes me curious as to whether the Scangauge remains on all the time, or does it have a way to turn itself on and off automatically?

I guess I might be able to mod the ELM with a little power switch, but I'd like to hear comments from any of you with experience of either the ELM or Scangauge.

/ Mike

February 4, 2012

I wondered about this myself, and found that the ELM device was still discoverable on bluetooth with the ignition off. This will also cause a drain on the Battery. I recommend removing it when not in use. The BT radio in my ELM died after a couple of months--another reason not to leave it powered up.

February 4, 2012

I wondered about this myself, and found that the ELM device was still discoverable on BlueTooth with the ignition off.

Yes, I was having a play today and my Android/Torque found it, but then just polled round each protocol in turn, so it would seem the ECU was not talking.

The BT radio in my ELM died after a couple of months--

Ouch, but at about £15 incl postage one can't expect too much I suppose.

I've done a bit more research now and it appears that the OBD-II specification is indeed for the power (on pin 16) to be Battery voltage and not ignition, so this must be the way it is. I've now opened my ELM up and fitted a small switch in the line from pin 16, so I can just leave it plugged in. Very simple job ... once I worked out how to open the case :unsure:

(I'm sure I have a small 12V relay somewhere, so maybe I'll fully automate it off the ignition sometime - depends how much I actually end up using it.)

Any Scangauge users out there? What does that do when the ignition is off?