parasitic drain....before I go nuts

[scubajim20]

My car was dead after sitting for a week. The battery and alternator are 1 month old. The alternator was replaced after we discovered it was over charging and putting the car if transmission failsafe mode.

I looked at dozens of threads and one common failure point was the FSU, mine was asymptomatic but I replaced it with a new OE unit from FCP. It did not resolve the issue. Last weekend I noticed my left blinker bulb was intermittent. I R&R it and I noticed the wire contact on the old one was slightly melted into the plastic base so maybe the over voltage did cause a problem. I purchased a digital battery/alternator load checker. Everything checks good except it says I need to charge it when it sits for 24 - 48 hours (11.8, 11.5, 12.03v). I am in the process of checking mV across the fuses. The car does go to sleep after 16 min.

My question, if there is a drain during sleep, shouldn't there be a voltage measurement across the negative terminal and the ground wire connected to the cassis? As what I am looking for across a fuse? This is where my electrical theory is weak.

[ross1]

Re-man alternator?
A bum voltage regulator can cause a "mysterious" drain. Disconnect the battery lead to the alt and leave at rest to check.

[JimLev]

Are you sure the overvoltage from the bad alternator didn’t cook your battery?
As for voltage drop from the battery negative post to chassis ground it would be very low due to the gauge size of the cable.
Will your meter measure as low as 0.0001 millivolts?
I’ll be back in the garage shortly and can measure mine.

[scubajim20]

I'll pull the battery lead and check that tomorrow. I was hoping the battery checker would give me that information but it tests good. My old fluke doesn't read that many places. If I am looking for 40 mV or > across the fuse, why shouldn't it be across the short cable from the negative side of the battery to the chassis?

[R Shaffner]

I'll pull the battery lead and check that tomorrow. I was hoping the battery checker would give me that information but it tests good. My old fluke doesn't read that many places. If I am looking for 40 mV or > across the fuse, why shouldn't it be across the short cable from the negative side of the battery to the chassis?

Jim, I think you're referring to a trick that Timm Meek shared, about looked for very slight voltage drop across a fuse as a way to see if a circuit is passing current. I've never tried it, though I might sometime. Sounds like a neat trick, but I suspect it might be hard to do because different fuses would show different voltage drops, and it can be hard to look for such small changes.

The chassis ground wire is supposed to be connected to the negative post of the battery, and therefore it should have the same negative charge. That is, there shouldn't be any voltage difference between them.

The usual way to look for a short is with an ammeter that measures current flow (amperes, or amps), not by measuring voltage. These cars make that tricky because they have some circuits that are meant to be always on. (That is, they don't go through the ignition switch.) And many meters (like mine) can't handle high amps for any length of time.

Here's a thread that describes how I traced and solved a short on an e34. If you have or can get a meter that measures amps, then you can try the steps I describe about letting the car go to sleep and then checking for which circuits might be pulling more amps than they should.

https://www.bimmerforums.com/forum/s...n-quot-Circuit

[CPHES]

Ross has a good plan. Let it go to sleep, then disconnect the battery. Let it sit until you need him again, and connect it up. If the car starts, it’s not the battery. I got a Ctek maintainer, and it has an accessory connection that blinks green/yellow/red based on battery voltage health. I kinda like it.

[Chedley]

You replaced the bad overcharging alternator AFTER replacing the battery, Yes ??
If so, I bet your battery has been cooked and cannot hold the charge for too long. No parasitic drain can empty the battery that fast.
Load test it, or better, return it and replace it with a new fully charged battery -it is probably still under warranty-, and all we be good.

[300kplus]

You replaced the bad overcharging alternator AFTER replacing the battery, Yes ??
If so, I bet your battery has been cooked and cannot hold the charge for too long. No parasitic drain can empty the battery that fast.
Load test it, or better, return it and replace it with a new fully charged battery -it is probably still under warranty-, and all we be good.

Chedley’s got a good point. I have a 98 E39M 62 that drove me bananas because of a parasitic leak. One thing I know about these cars is if it’s a battery issue they go completely bonkers! Just from experience I would start where Chedley is suggesting although you’re in good hands with the all gentleman chiming in on this post. I subscribed because my ‘98 has been sitting On account that my barn has an 01 e39 M62 and a ‘13 E70 and not a lot of time to drive all of them. I’m trying to decide if I should sell the 98 or turn it into a restoration product as she has high miles and needs some TLC…


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[JimLev]

Jim, sorry for the delay.
I uses my DC amp probe and voltmeter on the battery negative lead.
When I opened the trunk, which awoke the electronics the current flow thru the negative battery lead was 6 amps. The voltage drop across that short section of cable was 0.9 millivolts or 0.0009 volts.

After the car went to sleep the current flow thru the negative lead dropped to 33 milliamps, 0.033 amps.
The voltage drop was then 0.09 millivolts, 0.00009 volts.

Measuring the voltage drop across all the fuses is a PITA.
The following parts are generally the item that drain a battery, the FSU, stereo amp, Aux fan on tu engine cars.

[300kplus]

Chedley’s got a good point. I have a 98 E39M 62 that drove me bananas because of a parasitic leak. One thing I know about these cars is if it’s a battery issue they go completely bonkers! Just from experience I would start where Chedley is suggesting although you’re in good hands with the all gentleman chiming in on this post. I subscribed because my ‘98 has been sitting On account that my barn has an 01 e39 M62 and a ‘13 E70 and not a lot of time to drive all of them. I’m trying to decide if I should sell the 98 or turn it into a restoration product as she has high miles and needs some TLC…


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I’ve had everything from a hood switch to bad fuses culprit mine…


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[blarf]

Jim, sorry for the delay.
I uses my DC amp probe and voltmeter on the battery negative lead.
When I opened the trunk, which awoke the electronics the current flow thru the negative battery lead was 6 amps. The voltage drop across that short section of cable was 0.9 millivolts or 0.0009 volts.

After the car went to sleep the current flow thru the negative lead dropped to 33 milliamps, 0.033 amps.
The voltage drop was then 0.09 millivolts, 0.00009 volts.

Measuring the voltage drop across all the fuses is a PITA.
The following parts are generally the item that drain a battery, the FSU, stereo amp, Aux fan on tu engine cars.

Right-o. Check for current not the voltage drop. If your battery is draining that quickly because of a parasitic draw there should be enough current to easily measure with your multimeter (altho be prepared to blow a fuse in the multimeter if it's real bad). I'd add the LCM to the list of things that'll kill your battery quickly, but hopefully you'd notice the lights staying on constantly.

[scubajim20]

I charged the battery overnight and it is currently disconnected. The weather is crappy and raining at the moment, so I'll try some testing this afternoon. I might just leave the battery disconnected for a few days and see how the battery tests when idle.

Yes,The battery was replaced before we discovered the issue with the alternator. A cooked battery might be the issue. I will continue with the advice/test you have all presented. Some of it might have to wait until next weekend.

[StephenVA]

Instructions and tips that might be of help

BMW Vehicle Parasitic Draw Testing
When your car battery goes dead overnight, usually either the battery is at the end of its life span, or you left something on, such as a light. Occasionally something is drawing power that's not of your doing. This is a parasitic draw, and it can cause the same result as leaving the headlights on: a dead battery in the morning.

1. Remove the negative side battery cable from the negative battery terminal.
2. Connect the black wire to the com input on the multimeter and the red wire to the 10A or 20A input on the multimeter. The meter needs to be able to read at least a 2 or 3 amps for this test to work. Connecting the red wire to the mA input on the multimeter won't work and could damage the meter.
3. Attach a multimeter (set the dial on the multimeter to measure Amps as per multimeter’s instructions) between the negative cable and the negative battery post. Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems "wake up". After a bit of time they will go back to "sleep".
4. If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
5. Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings) last. Perform the same steps for relays found in the fuse panel. Sometimes relay contacts can fail to release causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.
6. Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners' manual or service manual to find what circuits are on that fuse.
7. Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.
8. Repeat steps 1 & 2 to test your repair. The ammeter will tell you the exact numbers.

BMW Battery Draw Testing
If your Shifter light is on, the car is definitely staying awake.
Your Battery will go down within days. If the light is not on you can have a parasitic draw, while the car is in sleep mode. The only difference, is the second draw is from a module which can’t wake the system (not mission critical), and it will take a lot longer to discharge the battery.
Shifter light NOT on: (battery fully charged)
Find the ground cable on the battery, but do not disconnect. (the cable end connected to the body not the battery, is easier to handle.)
Connect the Positive lead from the “Fluke” to the body of the car (good ground)
Connect the Negative lead to the (brown) ground cable (you can puncture it)
Make sure it’s easy to disconnect the (brown) cable from the body, but don’t take it off yet.
Open the glove box and remove and disable the switch so the light will not turn on, locate the fuse box.
Start the car and run at idle, turn EVERYTHING on, and activate all the components (sunroof, windows, a/c, lights …..) run 5 min.
turn the car off and remove the key. Open all doors and trunk, and with a screw driver,
close the door locks so the system thinks all doors and the trunk is closed.

Now lock the vehicle with the remote.
The “Fluke” must be set up to “A” not “mA” otherwise you will blow the
fuse in the meter. Remove the nut from the ground cable and remove the cable from the stud. You meter will indicate around (300mA).
Let the car go to sleep. (16 min) minimum, if this is not happening start over.
After the sleep mode is on the draw should not be more then 50mA, if it’s more go to the glove box and start pulling fuses one by one and check the draw after each one, but do NOT re-install the fuse. Pull the fuse and leave it out
There are some fuses under the right cover in the trunk. If you pull a fuse and car wakes up start over (next time ignore this fuse). If you pull a fuse and the draw drops to around 50mA, read the label on the fuse, you will know which circuit is faulty.

Relay locked on - test
Take out your infrared temp gun and measure each relay. The one that is hotter is "on". Simple!

The cheap parking sensor idea is free

[philly98540]

^ Great info!!!!

[StephenVA]

Been posted approximately 15 times, especially the no cost bumper saver

[300kplus]

Love!!!


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[scubajim20]

Great info I did see this on my search and I was going to come back to it. The battery is fully charged and the negative cable has been disconnected since monday. The car does go to sleep. (trunk and shifter light out after ~ 16 min) I plan on doing some testing this saturday.

[BimmrMeUpSnotty]

Stevie needs a sticky.

[StephenVA]

Naa, I will just keep posting away!

[ross1]

Great info I did see this on my search and I was going to come back to it. The battery is fully charged and the negative cable has been disconnected since monday. The car does go to sleep. (trunk and shifter light out after ~ 16 min) I plan on doing some testing this saturday.

Any resolution?
I mentioned my suspicion of a bad alternator before(voltage regulator diodes) and am wondering if you looked into it. If the diodes are leaking the alternator could be warm in back as it drains the battery.
If disconnecting the batt terminal at the alt. stops the drain you have your answer.

[StephenVA]

You mean it is not the 25ft of aftermarket audio wiring?

[scubajim20]

The battery held the charge over the week. It appears the battery is good. I just disconnected the connector on the alternator, and I will recheck the voltage of the battery in a day or two. Hoping that's it as it was the only thing replaced prior to this occurring. I tried the procedure with testing amperage but as soon as disconnected the brown wire to the chassis the car alarm activated. I assumed the probes through the meter would complete the circuit to avoid this but here is where my knowledge base ends again.

[ross1]

With a hot battery and the alt connected(cold engine) does the alt get warm?

[scubajim20]

I just measured with the infrared thermometer. It has been disconnected for an hour. So this may not be useful but it was the same temperature as the rest of the components.

[ross1]

I just measured with the infrared thermometer. It has been disconnected for an hour. So this may not be useful but it was the same temperature as the rest of the components.

The alternator would be need to be connected to a hot battery when doing this.