Parasitic 12v Battery Drain - ECU B fuse?

welcome! are you sure it's not under warranty?

can you give us the stone cold battery voltages on the new battery, starting with pre install and as you tested it?

 

looks like you need a schematic to see what the ecu feeds. hopefully, someone here can help. all the best!

 

Well, as you mention it, I did notice you seemed unsure whether what you had measured were amps or volts.

That would be worth going back over to make sure you're sure. I assume that when you talk about your 'voltmeter', you really have a multimeter that lets you measure more than just volts. (A typical multimeter lets you choose at least volts, amps, or ohms, and often several other things.) There should be some kind of selector on the front. You might want to repeat your measurement, but double-checking to make sure your selector was on amps.

If you did happen to measure in-circuit like that, but set on volts, you would get some sort of voltage reading, but it wouldn't be anything easy to interpret (it would be a mathematical combination of the car's leakage and your meter's impedance, and that's more complicated than we want to get).

If you were really set for amps and reading 6 or 7, that is a really high leakage current. How high? Well, I think a Gen 3 aux battery is rated about 46 amp-hours, so a drain of 6 or 7 amps would be enough to fully discharge it in under eight hours. That sounds more severe than what you were reporting.

If you did have the meter set on volts by mistake, and you were reading 6 or 7 (that is, about half normal voltage), that would tend to suggest the car's sleeping loads are roughly equal to your meter's impedance, and therefore a lot smaller than you were thinking. So it's worth measuring again to be sure what you measured.

If you do end up having to chase circuits to track down a problem, your wiring diagram online at techinfo.toyota.com makes that really convenient, because it is pretty interactive, you can click on wires and terminals and components and follow them around the car, switching between the schematic views and the ones that show where things physically are, etc. Way faster than trying to keep eight of your fingers stuck between different pages of the paper wiring book.

There is something interesting about the way Toyota builds their wiring, there are these things called 'junction connectors' scattered around here and there. Instead of building lots of wire splices into the wire harness, they'll bring a bunch of wires out to the same sort of multipin connector that's used for connecting to regular stuff, only what plugs into it is just a mating connector manufactured with a bunch of the pins shorted together. The wiring diagram shows where all of these are, and which pins are connected to which.

I'm not sure exactly why Toyota builds the stuff this way, but a nice consequence (even if it's not the reason they do it) is that each one of these junction connectors can give you another place you can disconnect something and have access to measure different sections of a circuit in isolation from each other.

-Chap

 

Be sure the hatch is fully latched, too. If it's only half-latched (one click instead of two), you'll have a parasitic drain of about 0.7 amperes, even if the associated lights are off. (That will kill the battery within 3 days.) Another possibility is a defective or misadjusted switch there.

Check to be sure the interior lights are off when the doors are closed and the 3-position switch on the "personal" light fixture is in its center "door" position. If not, a door switch is probably misadjusted and you'll get the same 0.7-ampere drain

For whatever it's worth, normal parasitic drain with everything off and closed is about 0.02 amperes (20 mA). At that rate, draining a healthy battery would take several weeks.