After installing a National Luna Intelligent Solenoid and Battery monitor, I quickly noticed that my primary battery was draining noticeably overnight.

I connected an EVM and found I had a parasitic drain of ~130mA. The solenoid+monitor are responsible for about 40mA of that, which left me with 90 mA to account for.

Once I started pulling fuses I noticed the OBD fuse was drawing ~30mA. I had Automatic plugged in under my steering column. Removing it removed this drain.

Automatic claims to only draw 5.5mA but that some vehicles enter "diagnostic mode" by default the second anything is plugged into OBD-II. Is that the case with our 3rd gen 4Runners? If it is the case, does being in "diagnostic" mode have any other deleterious effects on gas mileage, etc?

EDIT: writing this, I'm realizing also that the Automatic dongle might be woken up for a certain time period after connecting the battery, and that I probably need to give it some time to "go to sleep" after putting the EVM in series.

I don't think the OBD2 dongles ever go to sleep, I'm pretty sure they are constantly on. I bought an amazon one with an on/off button (iSaddle) and you could turn it off, but that one was junk so I returned it.

I don't have any experience with these dongles, but the Scan Gauge II I have stays active for a little while after you turn the ignition off. It's only a few seconds, but it wouldn't surprise me if a dongle would go to sleep after a certain amount of inactivity.

I bought one of those Bluetooth OBD reader things that you hook up to your phone and mine did that too. I thought I could just leave it plugged in when I got out of the car and left it, but it stayed on and almost killed my battery on me. After that I only used it occasionally because I couldn't leave it plugged in. Now I have a scangauge II and it turns off like 10 seconds after you turn off the ignition.

I had the same problem with mine, too. It never turns off. I learned the hard way and had to have AAA come out and give me a jump. I've been considering adding a small switch coming from pin 16 where the 12v comes from on the plug....just another project on the list of things to do.

I would recommend putting the switch off of pin 5 which is the ground. It's pretty common practice to switch the ground and not the positive wire on most simple automotive electronics.

-Steve

That's a good point. Pin 5 it is

Ack. If the Automatic dongle is staying at 30mA draw vs. it's 5.5mA sleep mode draw, that means the 4Runner isn't letting it go to sleep. If it can't go to sleep it means the presence of the dongle is triggering "diagnostic mode" on the truck. I'm not sure how I feel about driving constantly in diagnostic mode.

Have you ever thought of just unplugging it and putting it in your glove box? Simple solution. Mine's plugged in all the time but I use my 4Runner as my DD so it never sits for more than a day or two. But if I did unplug it I wouldn't miss it either, I just bought it to pull codes.

It isn't the ECU keeping the dongle on, there is a constant +12v wire at the obd2 plug in the car. If anything I would doubt the 5.5mA claim, I would believe your reading of 30mA assuming it was tested with a decent DVM (even the free harbor freight ones are ok). The car doesn't have a way to turn on/off anything at the obd2 plug.

-Steve