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battery drain diagnosis procedure?

The 90 S2 has developed the habit of draining its battery every couple of days. Replacing the battery didn't fix it. Aside from checking the grounds, what is the most efficient way to track down the culprit circuit(s)? I am thinking check the circuits by pulling fuses one by one and using the ole multimeter across the fuse connections. Any ideas? TIA SG

Old 10-07-2004, 01:49 PM
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Your battery drain should be less than 20 milliamps. You can isolate the circuit that is draining it by doing what you said.

Or you can put the multimeter in series with the battery at one of the cables then put the fuzes back one at a time making note of the ampere increases.
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Old 10-07-2004, 04:07 PM
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Often times it's the thermo-fan switch which fails and leaves the fan on. I haven't heard of them failing intermittantly, but I don't know. Maybe every once in a while it sticks on all night.

I only mention this in case your plan (which is good) turns up nothing. Lawrence's plan is probably more conveneient. I'd pull the fuses out one at a time until the current drops to keeps things straight. But whatever.
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Old 10-07-2004, 07:26 PM
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Re: battery drain diagnosis procedure?

Quote:
Originally posted by skipgresham944
The 90 S2 has developed the habit of draining its battery every couple of days. Replacing the battery didn't fix it. Aside from checking the grounds, what is the most efficient way to track down the culprit circuit(s)? I am thinking check the circuits by pulling fuses one by one and using the ole multimeter across the fuse connections. Any ideas? TIA SG
hey !

basically yes, put a DVM set to millis, remove the neg battery lead and put the meter in series.

DO NOT ATTEMPT TO START THE CAR

as said, reading should be about 20 millis,
pull out a fuse at a time.

usuall suspects

1> glovebox light not going off (switch)
2> alarm, backup battery for alarm, should be switched so that it only charges when ignition is on
3> fan motor not going off after a couple of minutes of ignition off
4> the radio amplifier for the aerial is not wired through the ignition switch and is on all the time
5> alarm circuit for stereo removal is mis wired and is therefore on

HTH

any further

holla back
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Old 10-08-2004, 03:07 AM
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The fan isn't running abnormally so it must be somewhere else. I will post what turns up...
Old 10-08-2004, 06:08 AM
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(happened to see this, i'm normally in 356 or OT)

Some things you can ony truly appreciate until you own a 6v 356

Put a 'meter between the battery and one of the cables. One by one, pull each fuse, and see when the draw stops. If there's more than 1 fuse with a leak on it, pull all the fuses, replacing one at a time, and when it starts to draw, something on that fuse is whats sucking the power.
Old 10-08-2004, 04:21 PM
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It was circuit #11 (interior accessories) - current draw is 30-40 mA when its fuse is in place, less than 20 when its pulled. All other circuits keep more or less steady current. Unfortunately, I can't find anything listed for that circuit continuing to operate when the key is turned off, other than the clock. The glovebox lamp and interior lamps aren't staying on when they shouldn't. For now, I guess I will just run without that fuse and figure this out sometime.
Old 10-09-2004, 08:42 AM
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You haven't found the problem if you only located 30 to 40 mA draw at maximum. You probably have around a 63 amp hour battery. Do the math - sucking down just 30 amps of the battery charge at 40 mA would take over a month. To knock your battery flat in a couple days you are looking for a drain around 1000 mA.

And don't bother looking at the grounds as that is not the problem here. Put your multimeter in series with the positive cable with the keys out and it should show up. With a new battery not changing the problem, the only other thing would be that you are somehow soft shorting the battery posts, not enough to make sparks but enough to cause a drain. Maybe to the hood?
Old 10-09-2004, 09:25 AM
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skip, by any chance when you open your drivers door does the ringer go off? I know the ringer is only supposed to go off if you leave your keys in the ignition and if you leave your lights on...but mine seems to go off all the time. I just bought a 944 and im trying to work out the few quirks it has.

I only ask because i noticed this and found it to be weird. The battey that came with the car was completeley dead when i started it up after about a weak of sitting at my house. Im not sure if its just a bad battery or there is something draining it like with the problem you are having. I jumped the battery and went for about a 45 minute drive. I made the mistake of stalling going uphill (new to driving stick) and could not get the car restarted (car wouldnt even turn over). Luckily i was only about a block away from my house . I replaced the battery with the one from my 924S and everything is fine at the moment. It may just be a bad battery, but im a little weary of going out on another drive to learn there is an issue with the battery being drained.

Edit - from reading another post over on Rennlist, check to make sure if you have powerseats, the switchs are returning to the neutral position. Apparently one user had a problem with this on a different car. I noticed that one of the switches on my drivers side seat does not work...might be worth taking a look at.

Im also thinking it could be related to the aftermarket alarm installed on my car. There was a hack job on the wire harness on the battery cables...perhaps even though the alarm was diconnected sometime in the lifetime of the car, its still causing issues.
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Last edited by Techno Duck; 10-09-2004 at 09:40 AM..
Old 10-09-2004, 09:31 AM
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Jon, there is another condition when the ringer/buzzer will go off. If you shut the car down, pull the keys and flip the turnsignal stalk to one side or the other to engage the "parking light" feature, the buzzer will go off when the door is open. But stop when you shut the door.

So keep this in mind. I would first check to see if this parking light function works - the side you flip the turn signal stalk to will light up those side markers constant. Then look at a wiring diagram to see how that parking light function is supposed to work. Maybe you have a bad switch or relay(s).
Old 10-09-2004, 09:53 AM
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iceshark-

Thanks for the info. The battery positive terminal has a plastic cap on it to prevent the shorting problem against the hood.

The way I found the interior accessory circuit issue was indeed to disconnect the battery and put the multimeter in series with it as you describe, and then pull fuses one by one. With the #11 fuse pulled, the draw returns to about 20 mA, and about doubles with it back in.

techno-

No, the chime does not go off if the door is open without the key in the ignition.

I did notice that when opening the passenger door while doing these tests, the draw goes way up even if the interior lights are not lit. The alarm system circuit showed no change with its fuse pulled. Not sure if any of that is relevant but I am grasping at straws at this point. For now, I am running with the 11 fuse pulled to see if the battery holds its charge, and doing without a clock and interior lights (and cig lighter, dammit - no radar detector use for now!!) SG
Old 10-10-2004, 05:48 AM
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Skip, you have a new battery, right? Assuming your meter's scale is somewhat accurate you just proved you only have a maximum draw of 40 mA. Not enough to knock your battery flat in a couple days.

Hook your multimeter leads up and feed them through the gap between the hood and windshield. Close and lock the car, including hood which may be pinching some wires, up and watch. If it is still 40 mAs then there can only be a couple things left. The drain is somehow intermittent (you would need a pretty fancy meter to record that or be lucky and catch it) or you have dirt/whatnot on the battery case. I have seen dirty batteries flow current from the positive post to ground and they die like your's is.

Or your new battery is defective, it does happen. Pull the battery out, charge it up, let it sit for a few days and see if it can hold a charge.

There isn't much else it could be.

Old 10-10-2004, 08:07 AM
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