OBDII devices draw power when the vehicle is turned off [except OBDPro if you get one with a special module].
I wanted to start a thread to see if anyone with a Bluetooth OBDII unit is having battery draining issues. Since it only draws a small amount of current it would take like 2 days of not turning on ur car to drain ur battery. Has anyone experienced this? I'm thinking this is the cause of my battery issues since i can connect to my OBDII connector when the car is off.
So this is probably my problem. I need to hook a DMM up to my car when it is off and see what the power draw is. I would think that USB OBDII scanner would be powered by the USB port so when the carputer turns off then it would turn off as well. Is this inaccurate?
The only OBDII scanner that can draw power from the USB port right now, AFAIK, is the OBDLink; and that's mainly useful for upgrading the firmware without dragging an appropriate computer to within USB-cable-range of your car. Doesn't actually serve much purpose outside of that [eg, the firmware update tool is windows-only, but you have a Linux or OSX carputer - specifically, I personally found it very useful :-)].
The OBDII port actually provides an always-on pin connected directly to your battery. Only the OBDPro currently has an option to stop drawing power while the car isn't on.
I posted this in another thread but i'll post it here to-this really isn't as big of a problem as most people think. The elm and other chipsets are designed to run on 5v. Usb Bus power is 5v. For a few reasons though, most scanners use the constant battery line regulated to 5v instead of the 5v usb. I image the OBDPro does it the correct way.
There are a few easy fix options here:
1. Solder a jumper to the obdII chip and clip the vbatt line.
2. (EASY) Cut the VBatt line in your obdII connector (Vehicle Side) which is pin 16. Connect Acc power. Now your OBDII reader will only run when the car is running and prevents any battery drain conditions.
3. Get an OBDII extension cable and soldier in a switch to the vbatt wire.
You're right that those are easy fixes, but I'd argue that telling someone to bust open their 150 dollar investment and take a soldering iron to it isn't really that friendly to a lot of users. I know that I'm unwilling to do it, for example [personally, I find it a lot easier to take the "unplug it when I'm not using it" route.
Yea I haven't really used it much so i'm thinking i may just rip it out and sell it.
But second to that I would think anyone who ran the switched power for their carpc would be comfortable switching the power wires on the OBD connector.
Most OBD-II devices will be powered from the OBD vehicle connector port - thus your problem.So this is probably my problem. I need to hook a DMM up to my car when it is off and see what the power draw is. I would think that USB OBDII scanner would be powered by the USB port so when the carputer turns off then it would turn off as well. Is this inaccurate?
Depending your application, you may find one or two low-cost units that will be USB powered. If you want something higher-end though, consider the Drewtech Mongoose series - I have a Mongoose FEPS, and it is USB powered, thus do not drain the car battery.
Be aware it makes use of the open API J2534, so will not work with your regular frontend at this point in time - I can only hope someone will make a plug-in for the new CF Auto about to be released
Hi mate, some good options.
Option 1: As chunkyks said some people would be reluctant to open their $150 device and start messing around with it potentialy causing damage if done incorrectly.
Option 2: Modifying the car wiring can have implications with the warranty on the car.
Option 3: I think i would take the basis of idea 3 and modify it slightly. I would use a relay instead of a switch to make it automaticly turn on once the car is turned on.
Get an OBDII extension cable and hook up the power wire to the N/O (Normaly open) relay contact.
Take a switched 12v acc power and an earth/ground wire to the coil of the relay.
Every time the car is turned on the switched 12v would power the relay coil, causing the N/O contact to "Close" allowing power to pass to the OBDII device. When the ignition is turned off the power is lost from the relay coil dropping out the contact.
If anyone has any questions i'll be happy to help