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Battery Drain

53K views 30 replies 16 participants last post by  5speed 
#1 ·
Good Day!!

I have a 2002 325xi with 144000km on it, about 7 months I replaced the original battery thinking is was dead, never had it tested. 5 days ago my new battery died so I had it re-charged and tested. No issues battery is not faulty.

On Sunday I checked the voltage, everything seemed OK volt meter read between 13.5 and 14.4. Today after work my car started but barely, I did have an appointment for the dealership today to get the car diagnosed.

Went to go start my car, battery dead again. Ive been reading the forums all morning and came up with different ideas as to what the problem might be ie FSU, alternator, a short somewhere.

I do have one warning light on my dashboard, the rear right light is red and that has been on for a while. Once I turn on my lights it goes out though.

I'm hoping to get the car to the dealership tomorrow now, is there anything else that might be making the battery drain this much quicker? Any help would be greatly appreciated, thanks in advance!!!
 
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#2 · (Edited)
What you should do is to unhook the ground on your battery and hook up your voltmeter between the negative terminal and ground. Probably use the milliamp scale. That should now measure a level of discharge. Now go to your fuse box, and pull each fuse, one at a time, and note any change to the level of battery drain. If something makes a good sized difference, you found what's causing your battery drainage.
 
#3 ·
Canada, eh?

It could be nothing...as in nothing more than you don't drive enough for the power you're using...those heated leather seats, the sub, the defroster and wipers...and all you do is drive 5 miles to work and back. That's theory one.

Connections on battery might be tightened but not tight...some terminals are just a little too small for our cables...might have been good enough at one point (small odds, but pull up on cable to test)

Sansho's test can tell you amount of drain, though remember some systems stay on for at least a half an hour after shutdown...it's got thinking to do I guess.

Then you start pulling all the fuses...and that light of yours stays on all the time but goes off when you start the car? Check ground fix if taillight...check loom from body to trunklid, if you mean one of the trunk lid lights...and if you can find the light, consider reverse or license plate lights...
 
#4 ·
Best not to let the negative terminal to battery post disconnect if possible. The reason for that is that if you disconnect it first it will remove power from every device. It's possible there is a device in the car that's not going back to sleep when you stop the car and removing the power completely resets it.

Instead set up your ammeter and connect it between the battery post and the terminal. Then remove the terminal from the battery post (breaking the main circuit) but keeping the ammeter connected (and then it takes over the connection measuring at the same time). That way the connection is never broken. It can be a bit tricky to do right.

Do not turn on the ignition (and definitely do not start the car) whilst the ammeter (assuming a regular sort of multimeter) is series. Even on a 10A range, it's likely the car will need more and blow the fuse at best.
 
#5 · (Edited)
Thanks guys, unfortunately the car is currently at the dealership, there going to do a system test. They were not to impressed that I have an aftermarket battery, almost like there going to put the blame on that. If they do not find the root cause then I will defiantly test each fuse.

As far as my drive to work lol yes good call dmax I do have a short drive to work but I drive regularly before work. Although some weeks yes its to and from work.

I charged up the battery last night car started fine this morning, drove to the dealership, I mentioned the rear tail light and the dashboard light associated with that. I passed on getting it checked for now as I wanna know the results of the test.

Just recieved a call from bmw and it is the resistor blower motor. Quite expensive to fix and they told me my theremostat is stuck. My car does not overheat nor does it take a long time to get to temp. I dunno if i will be doing that repair. Thanks for you help guys.
 
#7 ·
The Blower Motor Resistor (properly referred to as the Final Stage Resistor, or FSR) will not lead to battery draining. It will cause the fan in the Ventilation System to not function properly -- the fan speed selector will not work right, often causing only High Speed operation of the fan.

The red light that indicates a tail/brake light error is problematic though. You have a bad ground that needs fixing. Remove the tail lamp assembly look inside of the connectors, both on the car-side and on the lamp housing-side. On the car side of the connector, one of the pins has a BRN wire going to it, check that this pin is not burned off on either side of the connector.

You're posting from the Great White North, where the average daily temps are 3 million degrees below zero at this time of year. This is a very harsh environment for a battery, and if your battery is a Cheap Street battery, then I'd have to wonder if it is any good. I know you said it tested okay, but it sounds like it is objecting to the cold weather.
 
#9 ·
Check to make sure your battery cables are TIGHT
 
#21 ·
But isn't there a way to just test it with a multimeter? I tried this morning putting the positive terminal on the alternator and negative terminal on metal parts in the hood but with no reading..
 
#23 ·
I have this same battery drain problem. I did the same ammeter test and after pulling every fuse and waited till the car is in sleep mode, the drain persists! .147amps! This electrical gremlin has so far drained 3 different batteries so low that they couldnt be used any more.
Anyone have insight on a solution?
 
#24 ·
Have you really pulled every fuse though? I assume you mean one at a time only. Fuses are early in the circuit so if they are truly all out everything should be disconnected. About the only part that may not be protected by a regular fuse should really be the starter (not 100% sure in the E46). So that would mean a short circuit somewhere in the supply wiring.

Disconnect the battery positive and measure the resistance from battery cable positive terminal (not the battery) to ground (with all the fuses out). 147mA implies about a 100 ohm load which should be easily measuable.

Taken it to an auto sparky?

When it's running does everything electrical work properly?
 
#25 ·
Thanks for the replies guys but I actually purchased a new batt from Walmart and all is good now. The climate control seeped power while I was away for a fews days and the battery wasn't able to hold any charge afterwards. Multiple jumps and no way of holding charged killed most of the cells, but it's all good now
 
#26 ·
The 147 constant drain was with every single fuse under the glove box out, FSR unpluged, block with fat harness under hood unplugged and even unpluged some wire harness coming from the radiator fan area. STill draining those 147 mili amps

i dont know what an auto sparky is so no.
When i turn the car on on a warm day the turn signals dont light up, ac doesnt work, radio diabled, keyless entry doesnt work. When cold car seems to be normal...
Thank You
 
#28 ·
I cant afford to go to the auto sparky at this time. I tried using the wiring diagram in the link you provided as it looked extremely usful but the image would not display...

i am quite suspecious of the wiring going to my tranny. Before any of these strage things started happening my transmition would at random times go into some type of safe mode and display a gear with (!) inside. I would restart the car and everything would be fine. Now the gear symbol stays on all the time and the car drives normal. I wonder if they are related...
 
#29 ·
You need to have the Adobe SVG Viewer installed. It's a bit hard to get a decent image to attach here. Just search for battery and it's pretty simple. One branch to all the fuses. And one to the alternator and starter. Also the alternator connects directly to the battery. I would try disconnecting the starter and alternator separately.

If you've removed all the fuses I would not expect the transmission to be the cause of the battery drain problem.

Reading the codes also *might* give you somewhere to start.
 
#30 ·
Hello,

I am having the same problem with my car; battery drainage. I replaced the battery 2 months ago and now its draining. One thing i did not see in this thread is people posting their modifications that could lead to this problem. I am highly suspicious of any electrical mods. I have eagle eye LED tail lights, LED angel eyes, LED side markers, LED interior maplight/domelight ...I dont see though how that could drain all the power over night, you can run an LED on a AA battery for a whole day without draining it...

sometimes I DO get a tail light out dash light (because of the eagle eye LEDs) but once I turn my signal on...after 3 clicks the tail light out signal turns off...that happened a few days in a row recently. not sure how that could affect it either. I did recently install the interior LED lights, but again how would it drain so much power, it should rain less than regular halogen bulbs. and plus...when the key is not in the ignition, interior electronics basically dont work because there is no power in the system.

any thoughts?
 
#31 ·
I had a battery drain problem with my 2002 M3causing my battery to go dead with a day or two. Isolated it to the CD/Navigation system on the left side of the trunk. The drain was about .7 amps. After unplugging the unit, battery drain was reduced to 40ma which the dealer says is normal. Replacement cost was $2700 so I passed on replacement.

Unplugging this unit kills the console display panel. I plan to put a switch on the power line to this unit so I can turn it on when I am driving and turn it off when I stop.
 
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