Jerry From LA SuperDork
Jan. 11, 2017 5:27 p.m.

Hello Everybody,

My wife's 2010 Sienna has a short circuit that killed a battery. I'm looking at over 40 different circuits spread between three fuse boxes. I'm gonna start by disconnecting the negative terminal on the battery and pulling fuses. My first question:

  1. Is there a known failure place where I can look and maybe cut my workload down? The only thing I found was a recall for faulty seat heaters but I don't think her Sienna is equipped with them.

  2. The little fuse puller thingy was missing out of the fuse box. Is there a substitute I may have in my toolbox that won't nick/ crack/ destroy the fuse? They're the micro-blade type. I can't even get in there with my smallest needle-nose pliers.

Thanks in advance,

Jerry

Dr. Hess MegaDork
Jan. 11, 2017 5:43 p.m.

My friend is going through this same thing with his 98 Camry. I suspect the alarm/remote entry module, but it is just a hunch at this point.

Put an amp meter in the negative battery lead to ground, then start pulling fuses and watch the current draw for a change. Keep in mind that when you first hook it up, the draw will be greater, then reduce as the ECU boots up. So wait for it to stabilize before you start pulling fuses. Then pull the relays one at a time too. Some of them have power all the time.

Streetwiseguy PowerDork
Jan. 11, 2017 5:52 p.m.

First, make sure the glovebox is closed properly. Take a peek with through the windows in the dark, look for a glow from something that shouldn't glow. Then unplug anything not OE Toyota.

As in the advice above, turn everything off, ammeter in series from the negative cable to the post. If you need to have a door open, latch the striker with the door open so it doesn't keep the body module alive.

Wait 30 minutes or so, and the draw should be down below 40mA. If its not, pull fuses until it drops, then science out what that circuit feeds. If the draw after its asleep is more than 200mA, something major (like an alternator) is on or shorted.

I hate parasitic draw diagnosis.

Jerry From LA SuperDork
Jan. 11, 2017 6:06 p.m.

My VOM will do 10 amps. Hope that's enough...I usually put the probes between the negative batt terminal and the disconnected negative cable. Since I didn't have a fuse puller, I started with some of the low-hanging fruit like the ECU relay, etc. I'd rather have my wisdom teeth pulled than do a power draw diagnosis, especially when even the interior lights are connected to some type of microprocessor. This thing has more circuits than my house.

Dr. Hess MegaDork
Jan. 11, 2017 7:21 p.m.

10 amps is more than enough. The draw is probably less than 1 amp.

Jerry From LA SuperDork
Jan. 11, 2017 8:16 p.m.

Probably. it could be quite a bit if an alternator diode has shorted. First thing, I'll be pulling that wire and comparing.

Jerry From LA SuperDork
Jan. 11, 2017 9:27 p.m.

Right now, immediately after disconnecting the battery, the draw is 76 milliamps.

Jerry From LA SuperDork
Jan. 11, 2017 11:05 p.m.

An hour later, same amperage.

dculberson PowerDork
Jan. 11, 2017 11:50 p.m.

That's not out of the realm of reason. Are you sure the battery didn't just fail from age?

Jerry From LA SuperDork
Jan. 12, 2017 12:13 a.m.

In reply to dculberson: The batt was exactly two years old which is why I'm looking for causes. Yeah, I was a little shocked too but I had the VOM set to 10 amps and it read .076 amp. I still have the negative cable removed so tomorrow I'm going to pull the alternator wire and re-test. It's entirely possible the batt itself shorted out. They don't last long here in CA with the underhood heat in the summer. Much more than four years is some kind of miracle. However, the thing should last more than two years.

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