To test for a battery drain problem, what's the correct way to measure current draw at the battery with everything shut off? Can you measure current draw somehow and pull fuses with battery still connected? Maybe measure current across each fuse - with or without fuse in place? At the risk of asking a dumb question, I guess that connecting a multimeter to measure current across battery terminals would short out the battery, is that right?
So should you disconnect ground cable from negative battery terminal and use multimeter to measure any current flowing from negative battery terminal to ground cable while systematically pulling fuses? What should be a normal amount of current flow with everything shut off? (I assume there is always a small current flow needed to power various memory systems)
To measure the current drain from your battery you will need to connect your multi meter in series with the battery and NOT in parallel across the positive and negative terminals. This would be OK to do this if you are measuring voltage. To measure current disconnect the negative terminal (I use the neg but you can use either), set your millimeter to measure amps and connect the meter between the battery terminal and the disconnected cable. If you don’t have an amp meter then use a 12V test light bulb. The bulb will have a very low glow due to the current drawl from your clock, computer, etc. If the trunk light is on you will want to pull the bulb or fuse. If it is brighter then a low glow then you have a short somewhere in your car. If you want to see what the difference between a low glow (low amp draw) and a high amp draw turn on your head lights. You can pull each fuse and see if there is a change at the amp meter or pull the fuse and insert the amp meter across the fuse terminals (need to reconnect the battery of course). Checking each fuse (by pulling or direct measurement) will tell most problems except if you have a worn wire short on the hot side (positive) of the fuse box which is very unlikely.
Thanks efdoyle3!
There's one set of fuses in the glove box and another set in the trunk - do I need to test all of them? What's a normal amp reading from just the clock, computer etc and how high of a reading would point to a malfunctioning component? What are the most likely suspects for abnormal battery drain?
a test light would be the best way, also relays sometimes stick and create a current drain, sometimes they aren't protected by fuses, I had a defroster relay stick in an old Maxima I had it fried two altenators and as many batteries GL
Before you test for the parasitic drain be sure a wait 20 minutes after the car is off for the computers to shut down.
Hook up you ammeter in series with the negative battery cable to verify you have a draw.
The draw should be no more than 30 milliamps.
Check all you light bulbs to make sure they are off.
Then start pulling the fuses one by one.
I have a parasitic drain on my '00 528i. Water pump went out, serpintine belt got fried, and broke. Battery was dead so a friend and I hooked up a small battery charger: 12v - 6 amp. The leads got connected reversed ( black on + terminal, red on - terminal) and the charger ran for about 6 minutes before we disovered the problem. Now the battery won't hold a charge for more than about 3 days. Using a battery charger I have started the car and drove it for just over 2 hours straight, but if the car sits for a couple days undriven the battery is drained.
Could a specific piece of electronic equipment have been damaged by the reversed leads on the charger?? I wanna say voltage regulator, or something similar maybe??
Last edited by bimmermeupscott; 10-05-2008 at 12:41 AM.
Just Barely Not Illegal
1. Yesterday, when I hadn't started my car for a week since I unplugged the aux fan, I found the battery voltage didn't drop at all (it would usually drop to about 2 volts over a week without charging) so this seemed to indicate that the non-working aux fan was the battery drain culprit.
2. I decided to do proper battery drain test with digital multimeter connected in series to battery negative terminal. On connecting DMM I heard CD player making noises and DMM reading was 1.38 amps - dropped to 0.48 amps after about 1 minute when CD noises stopped (guess that's normal) but auto indicator light was now on so waited another 15 minutes until auto light went out and reading dropped to only 0.01 amps (computer in sleep mode) so apparently no abnormal parasitic battery drain.
3. Reconnected aux fan plug, DMM reading jumped a little to 0.03 amps, then after about 1 minute spiked again to 0.18 amps, suggesting there was a significant drain from aux fan. I never did find the aux fan fuse to try pulling it, but this way of testing does seem to confirm that my battery drain problem was indeed from faulty aux fan.
4. During the main battery disconnect process, I used a 9V AutoZone "memory settings saver" plugged into cigarette lighter socket and although I didn't lose my radio station settings, I still lost my clock/date/fuel consumption and other settings, so guess 9V battery couldn't handle the transient 1.38 amps battery drain? Has anyone else experienced this? Do those plug-in 9V memory settings savers usually work when doing a simple battery disconnect?
5. Now I solved one problem but possibly created another. The DSC, ABS and Brake warning lights all keep coming on now after a few minutes of driving. If I turn engine off and restart, those three lights don't initially come back on, but they do return after a few minutes of driving or even just when parked at idle. This begs the question could disconnecting/reconnecting the aux fan have triggered this problem with the three warning lights? Are they all inter-related anyway? BMWs seem to have such sensitive and complex electronics I can believe anything is possible!
Del 1999 540iA
Turn the wheel full lock either way and those lights should go....
Not sure, but my guess is that one way or another delfletcher resolved his issues sometime within the last 8 years......
<== Steptronic Sealbeach740
2000 740i sport: 74k Green/Tan chrome MPars, clear corners, quad brake lights, AIC hi-beams, Hoen fogs, 16x9 screen, MKIV, TFT LCD screen in back, license plate backup camera with "on demand" switch, iPod audio/video (CDC/iPod audio switching, iPod video on 16x9 screen), Basslink, gauge rings, ///M pedals, switched steptronic +/- shifting mode, E46 paddle shifter steering wheel, Dinan engine & tranny software upgrade, DDEs controlled via Euro fog light switch, painted calipers with "BMW" lettering, windows up/sunroof close via remote.
2003 540i sport: 81k, Sterling grey/grey, MKIV Nav, PDC & CWP - Added license plate backup camera with "on demand" switch, paddle shift steering wheel, windows up/sunroof close via remote, Akebono's, painted calipers with "BMW" lettering, quad brake lights, iPod audio via AUX mode/video via 16x9 screen, BMW TV tuner, ///M pedals & gauge rings.
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