I attempted to help my brother with a confounding problem with his car this afternoon, and after a few hours of work, we were no closer to an answer than when we started.
Recently, his battery has been draining down overnight. He thought maybe he had a bad battery, so he got a new one. Same problem.
I went over there today and found that the car is drawing 1.6 amps from the battery even when turned off.
We started troubleshooting by pulling fuses. The car kept drawing 1.6 amps through all of them.
I pulled the main fuse, and the car still drew 1.6 amps.
For a while, we thought it was maybe the alternator rectifier, but that wasn't it.
We unwrapped the sheath from the main bundle of wires coming off the battery and found no shorts.
We disconnected the wiring to the starter and that wasn't it.
The car still draws 1.6 amps! We can't figure out what's doing it!
@MLE_online I’m a little fuzzy on the details, but it sounds like if there’s a loose connection, it will basically ground electricity into the ground, so it’s not really going into any particular device, it’s going into the ground, like a leak.
@MLE_online from both fuse boxes (the one inside too)? Generally the only thing not on a fuse is the starter motor. Haven't had a subi in a minute. busaru dot com might have the wiring diagram for it which could maybe help.
@cda Both fuse boxes! And yea, looking at the wiring diagram, the only things not on one of the two fuses boxes are the start motor, the headlight relays, and the horn relay.
@MLE_online whoa. Maybe check the main ground leads from the batt to the chassis? I don't know if newer cars stopped doing it, but a grip of stuff uses the chassis for return and if that lead isn't secure components can end up finding weird snake circuits back (a stretch as it probably wouldn't start if this were it). Last thought would be to pull the ignition relay (or other interesting relays heh). Could be a wedged relay keeping something on like the ignition coil circuit?
@MLE_online 1.6A is a suspicious amount for a continuous short. Seems more like a "stuck on" amount of current. Have a thermal camera? ~19 watts might show up (at night).
@MLE_online batteries are replaced and people still leave the lights on often enough that all cars neen to handle battery disconnect. In some industries europe mandates battery disconnect.
@bluGill right, but if he has to disconnect his battery every night, that's not going to be good for the car's operation. The ECU often takes a while to get itself settled down again after being disconnected from power.
Once in a while is fine, but every night is not good.
In any case, it still leaves a short somewhere in the car that needs to be fixed.
@MLE_online A friend's mother had the same issue, and I belive it is the same make and model you mentioned. He pulled the fuse to the On Star system and the issue stopped.
@MLE_online May be a job for an inductance tester? https://www.ebay.com/itm/395351715370 should be able to tell you which wires are hot without having to find or make contacts on each of them.
@MLE_online I had a draw down problem on the Jag, had to pull fuses one by one through 5 fuse boxes of fuses to isolate it. Found it finally. Good luck!
@misternineham I thought for sure it would be the alternator after we eliminated everything else and we even took the alternator to the auto parts store to be tested but that ended up not being it, which was such a let down
@MLE_online 😬😬😬 then my guess would be a failing wiring harness which will be a nightmare to troubleshoot.
It's possible there is a hidden lo-jack style system a dealer installed at some point where they cut it directly into the harness before the factory fuses. Usually they don't work too hard to hide them but sometimes they do.
I've seen them in the engine bay and under the dash.
@douglasvb that's all I can think of this point. We checked everything that should have been the problem and didn't find anything, so it's got to be in the wiring harness itself
@MLE_online What make/model car is it? I have a friend chasing an unexplained battery drain issue (although not quite THAT much standby current) in a... Mazda 3 I think?
Still actively investigating and no solution there either.
The wiring diagram on page 466 shows the battery being connected to MAIN SBF, which I assume is the one you pulled. Page 458 also shows the battery being directly connected to M/B No 14, related to to security indicator light.
Buddy of mine in college had a problem with the battery draining. After weeks of bullshit, it turned out he had his interior lights on at the lowest brightness but the dome light was out, and he parked under a street lamp at night. So nobody noticed the rest of the interior lights being on (in the door and by the floor boards)
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