Parasitic Drain Mystery

[Lox]

Hi everyone,
I have a mystery to solve. I've been dealing with parasitic battery drain since I bought my car (E39 535i 1999) in March 2020.
The facts about the drain are:

• it is present in both locked and unlocked "mode"
• I've tried every fuse in glove-box, behind glove-box, in trunk (both, the traditional and also the big ones above battery on (+) cable) - none of those fuses has effect on the drain
• I know that there are few fuses under carpet, but they are all covered by fuse F100 and disconnecting this fuse has no effect on the drainage (https://www.newtis.info/tisv2/a/en/e39-535i-lim/hZzP9c3)
• the drain doesn't occur after disconnecting and reconnecting the battery, so the traditional way (connecting the ammeter in series) to measure it fails - have to use clamp ammeter - the drain occurs again after switching key to the second position, don't have to start the car
• with clamp ammeter I figured out, that the drain is caused by the thickest (+) cable from the battery, which is leading only to alternator and starter (if I'm not mistaken) - based on this schema: https://www.newtis.info/tisv2/a/en/e...attery/uUDfIbo
• the drain is ~0.5A

So my question is: Could it be caused by alternator or starter? It seams really weird to be one of those, especially with the drain disappears after disconnecting and reconnecting the battery.

Thanks for help in advance and sorry for my bad English.

[ViolinARC]

Have you checked the FSU? That was the source for me and for 90% of others who have the parasitic drain...

[edjack]

The battery cable is also routed to the subpanel under the passenger seat. Have you examined it?

Finding parasitic current drain
An article in Motor magazine suggests this approach: measure the voltage drop across the fuse. It s/b zero. If you measure several (or more) millivolts, you can consider that circuit suspicious.
Some modules do not take kindly to pulling fuses, and you may encounter a lockup or damage. This approach avoids that, as well as the hassle of pulling fuses.
Also, this can identify blown fuses, where you will measure the battery voltage.
Here’s a table that relates current drain to voltage drop across fuses:
http://www.autonerdz.com/yabbfiles/A...crossfuses.pdf

More voltage drop tables
https://www.powerprobe.com/fuse-voltage-drop-charts/

[JimLev]

Every time you disconnect and then reconnect the battery all the modules will wake up and draw about 10 amps until things start shutting down.
You need an amp meter in series with one of the battery leads. As the modules start to power down the current will drop.
Don’t open the doors or touch anything, that will cause the modules to wake up.
IIRC my car draws about 20ma when sleeping.

[Lox]

Have you checked the FSU? That was the source for me and for 90% of others who have the parasitic drain...

Yes, I've checked the FSU and pulling the cable out from it while parasitic drain occurs has no effect on the drain.

The battery cable is also routed to the subpanel under the passenger seat. Have you examined it?

Finding parasitic current drain
An article in Motor magazine suggests this approach: measure the voltage drop across the fuse. It s/b zero. If you measure several (or more) millivolts, you can consider that circuit suspicious.
Some modules do not take kindly to pulling fuses, and you may encounter a lockup or damage. This approach avoids that, as well as the hassle of pulling fuses.
Also, this can identify blown fuses, where you will measure the battery voltage.
Here’s a table that relates current drain to voltage drop across fuses:
http://www.autonerdz.com/yabbfiles/A...crossfuses.pdf

More voltage drop tables
https://www.powerprobe.com/fuse-voltage-drop-charts/

I've covered testing of the subpanel by removing fuse F100 as I mentioned in my original post.
I can try the "voltage drop" technique, but I'm not sure that will help, as no fuse has effect on the drain when I pulled them out.

Every time you disconnect and then reconnect the battery all the modules will wake up and draw about 10 amps until things start shutting down.
You need an amp meter in series with one of the battery leads. As the modules start to power down the current will drop.
Don’t open the doors or touch anything, that will cause the modules to wake up.
IIRC my car draws about 20ma when sleeping.

Yes, I know the technique with amp meter in series, but the drain doesn't occur after disconnecting and reconnecting the battery, and my "normal" amp meter can't handle the current to successfully restore the drain after disconnecting the battery using switch key to second position. That's why I'm using the clamp amp meter. I think, that is not the problem, because its just another technique to measure the drain. Also, I wait 15 minutes, so the car can go to sleep mode, before the measurement. Conclusion: I don't think that the problem is in my measuring technique, but you can prove me wrong...

[JimLev]

First thing, you don’t have the key in position 2, it’s always in position 0 when your doing the test.
Wait 16 min before you disconnect the battery cable.
Can your amp clamp meter read as low as 0.020-0.050 amps accurately?

Most of the meters I have will only read a max of 10 amps. Here is the work around.
Disconnect one of the battery cables. Get a jumper lead that will handle 10 amps to connect the battery cable to the battery post.
Set your digital meter to a low milliamp scale like 1000 ma or lower.
Connect your jumper lead from the battery cable to the battery. Wait 16 min for the trunk light to go out.
Connect one meter lead to the battery cable you removed and the other meter lead to the battery post.
Now remove the jumper lead connected to the battery post leaving the meter lead connected to the battery post.
See what the current is reading.

[Lox]

First thing, you don’t have the key in position 2, it’s always in position 0 when your doing the test.
Wait 16 min before you disconnect the battery cable.
Can your amp clamp meter read as low as 0.020-0.050 amps accurately?

Most of the meters I have will only read a max of 10 amps. Here is the work around.
Disconnect one of the battery cables. Get a jumper lead that will handle 10 amps to connect the battery cable to the battery post.
Set your digital meter to a low milliamp scale like 1000 ma or lower.
Connect your jumper lead from the battery cable to the battery. Wait 16 min for the trunk light to go out.
Connect one meter lead to the battery cable you removed and the other meter lead to the battery post.
Now remove the jumper lead connected to the battery post leaving the meter lead connected to the battery post.
See what the current is reading.

Look, this is the procedure I'm using to measure the parasitic drain:

1. Unlock the car.
2. Open trunk.
3. Wait aprox. 15 minutes until the car goes to the sleep mode (trunk light goes out).
4. Using clamp amper meter measure the current with 1mA precision.

Note: I do nothing with the key, only unlock the car.

Before I got my clamp amper meter I've used the "classic" amper meter with cables using following procedure:

1. Unlock the car.
2. Open trunk.
3. Disconnect battery.
4. Connect the battery via amper meter (the amper meter is connected in series between the ground cable and negative battery post).
5. Wait aprox. 15 minutes until the car goes to the sleep mode (trunk light goes out).
6. Read the current.

However, I cannot use this procedure with "classic" amper meter, because after reconnecting the battery the drain is not present.

So there is kind of workaround to avoid the drain: After driving the car, before leaving - disconnect battery for a while and connecting battery back, close trunk, lock the car - drain won't appear, but this is so annoying to do this always before leaving the car. Also, I can imagine, that this could cause some other issues - disconnecting and connecting the battery so many times.
The drain reapears after the reconnecting battery after "booting all systems up" using key - switch to second position.

At the beggining I've bought new battery, but it didn't solve the problem.
So there is a parasitic drain, because after 2-3 days of not using the car, the car cannot start because of low voltage.

[edjack]

What is the most sensitive full-scale reading of your clamp-on? Does it measure DC amps? Only rather expensive ones, e.g., Fluke, do; the typical Harbor Freight ones do not.

[Ed CT]

So, you bought the car in March 2020. Did the previous owner add any unconventional electronics? Such as sound equipment, amps, radar devices. Look for any un-natural-looking wires near the DME box, battery, trunk compartments, center console.

[Lox]

What is the most sensitive full-scale reading of your clamp-on? Does it measure DC amps? Only rather expensive ones, e.g., Fluke, do; the typical Harbor Freight ones do not.

The resolution/accuracy of my clamp meter is 1mA in DC Amps mode. And yes, it can measure the DC amps and I set it to this mode and calibrate it everytime before measure.

So, you bought the car in March 2020. Did the previous owner add any unconventional electronics? Such as sound equipment, amps, radar devices. Look for any un-natural-looking wires near the DME box, battery, trunk compartments, center console.

That's good question. There were only two things that were not original. Radio and reverse camera above license plate, but I've change both of those things already and I was trying to find someting near the places that you mentioned, but no luck. Everything seems original. And even if I overlooked something, there should be some fuse which should cover it and I tried pull out every fuse, at least I think I did, according to the newTIS: https://www.newtis.info/tisv2/a/en/e...f-fuses/fuses/


The drain is located (according to my measurements) on the "left" line from positive battery post in this schema https://www.newtis.info/tisv2/a/en/e...attery/uUDfIbo
But it doesn't make much sense to me - there is only alternator and starter on this line and I cannot imagine how could drain the battery one of those.

[Chedley]

Well, the after-market reverse camera is connected to the "left" line from the B+ battery post, near an electric panel at the left rear corner of the car. As or if the camera is set to always-on, it drains the battery within a few days.....Do not ask me how I know this ?!

On your car, I bet the the previous owner has probably remove the reverse camera, but did not undo the connections.

[JimLev]

You said you removed F100, what about F101-F106? They are on that same circuit as the starter and alternator.

[Lox]

Well, the after-market reverse camera is connected to the "left" line from the B+ battery post, near an electric panel at the left rear corner of the car. As or if the camera is set to always-on, it drains the battery within a few days.....Do not ask me how I know this ?!

On your car, I bet the the previous owner has probably remove the reverse camera, but did not undo the connections.

Ok, I will try to find some suspicious wiring near the reverse camera

You said you removed F100, what about F101-F106? They are on that same circuit as the starter and alternator.

Yes, I removed all of these (they are above the battery), but they are not on same cable as starter and alternator. There are 2 cables going from the positive battery post. Unfortunatelly none of those fuses has effect on the drain

[Kevyo2]

I have a 2002 M5 and I had this issue. I worked for an OE as a Market Quality Engineer and worked on and solve many issues like this. This was a really tough one to find, the M5 has many " hot at all time circuits" and differnent systems go into sleep mode at different times. I started by bypassing the trunk and waiting the sleep mode and then pulling fuses. The problem is that sometimes it would waske up and a few times it would not start afterwards. Because it isn't a daily driver, I would just charge the battery during the day and then pull a fuse at night. The next morning I would check the battery voltage, if it was low (and it was a lot) repeat. Finally, one morning it was still at 12.6. I put the fuse back in and the next morning it was low, removed it and good voltage. The fuse feed 6 electrical components that were " hot at all times" so I put the fuse in and pulled the plugs on the three components. Next morning good voltage. Plugged in two (could do one) and it was OK. Plugged in the las tone, battery low. Pulled it, battery OK. If memory serves me correct, it was fuse 56 in the trunk, issue was the radio. The process is more important then the radio being the culprit as many things can do this. Try 56 first as it covers the NAVI, CD changer, Radio and two other things. I know the fan can run any time. My wife gave me a bunch of grief and ridicule saying I should take it to the dealer but I know how that would have gone. Some components have triggers to wake up like when a door is opened and a timer to shut off after X seconds. I had a vehicle that the trunk solenoid caused an electrical spike (normally key off) that caused a system to wake up but since it was a rouge signal, the timer never started so a 600 mA draw that drained the battery. This happened a lot at airports, a lot of angry people with new cars that won't start afte rreturning home from a business trip. Anyway, this procedure will work but it will take some time.

[Lox]

I finally managed to solve the problem!
The problem was a damaged regulator within the alternator.

Key facts for diagnosis of THIS problem:

• alternator/battery light on instrument cluster is not on, when ignition switch is in the third position (ON position - ready to start, but not cranking the engine)
• if you disconnect the positive cord from the alternator, the alternator/battery light on instrument cluster should be on, when ignition switch is in the third position (don't forget to isolate the positive cord, before re-connection of the battery)
• disconnection and re-connection of the battery remove the drain until you turn on the ignition switch to the third position again

Hope this helps someone with same problem

[seagreen323i]

Edited because I can't read


Glad you got it sorted out!

[Ed CT]

I finally managed to solve the problem!
The problem was a damaged regulator within the alternator.

Key facts for diagnosis of THIS problem:

• alternator/battery light on instrument cluster is not on, when ignition switch is in the third position (ON position - ready to start, but not cranking the engine)
• if you disconnect the positive cord from the alternator, the alternator/battery light on instrument cluster should be on, when ignition switch is in the third position (don't forget to isolate the positive cord, before re-connection of the battery)
• disconnection and re-connection of the battery remove the drain until you turn on the ignition switch to the third position again

Hope this helps someone with same problem

Happy to see that you resolved this. Thanks for the follow-up post.