Annoying Battery Drain

[llll1l1ll]

Hey Mafia,

I've been having this annoying battery drain problem for a while now. I just got a new battery because the original one died. No worries, that's not a big deal. However, I've noticed that after a day or two of sitting, it was weak to start. Strange. Just this weekend, it sat from Thursday evening until Sunday morning, and I had to get a jump. There wasn't enough juice in the battery to turn the starter.

I don't think it's the alternator, because once running, the car doesn't stop. A bad alternator would not keep the battery charged, and eventually the car would run out of voltage and not have enough to keep running.

Based on some basic internet research, I think the culprit might be the final stage resistor. Although I haven't experienced any erratic fan speeds, it seems to be the only thing I've noticed that causes this issue.

Does anyone else have any similar issues or any other suggestions?

Many thanks,
Pete

[Ryans323i]

To help narrow it down, can you eliminate definitely some less likely causes: Your lights aren't left on, all doors and trunk are completely closed, and there's nothing left plugged in the cigarette lighter for a power source? (this would be during the "sitting" period)

[llll1l1ll]

Yeah all the doors are shut, trunk is closed, and I don't have a GPS or in-car charger or anything. Sometimes, I forget I have a cig lighter. Plus, I would know if the doors/trunk weren't shut properly since the lights would stay on.

[johnrando]

Had the same thing, it was my FSR (no erratic fan speeds either btw).

[BavarianZHP]

More like a FYI: Doesn't the car shut off all of the lights (interior and trunk's) if it's on for more than 15 mins? It's a safety feature built to avoid draining the battery. I figured this out while I was working on the door last night.

[brettbimmer]

Is the car "going to sleep" as it should after about a minute or two once you turn it off? Never had a problem with this myself, but it would make the case for fairly rapid battery drain if it wasn't shutting off completely.

[Dave1027]

Does the car have an aftermarket alarm? Sometimes those induce parasitic loss. You can check for a leak of battery power by disconnecting the positive terminal and hooking an amp meter between it and battery positive.

[johnrando]

A faulty FSR can keep the car from going to sleep.

[brettbimmer]

^ Great to know John! I was wondering if that may be one of the causes. Thanks for the clarification.

[llll1l1ll]

Does the car have an aftermarket alarm? Sometimes those induce parasitic loss. You can check for a leak of battery power by disconnecting the positive terminal and hooking an amp meter between it and battery positive.

Nah no alarm on my car!


Had the same thing, it was my FSR (no erratic fan speeds either btw).

This is what I'm thinking. I found an FSR for like 50 bucks or so on bavauto. I'll probably order it today or tomorrow.

[danewilson77]

May be a good move as long as the $50 sensor is good and lasts.

Typically, for a sensor (exhaust or intake cps, fsr, etc) we would advise genuine BMW, or other proven oem sensor.

My $0.02

Sent from Williamsburg, VA USA.

[llll1l1ll]

Would Behr be a proven one?

[danewilson77]

Would Behr be a proven one?

Dunno.

Sent from Williamsburg, VA USA.

[aurelius]

Behr is the OE supplier. Photo below shows my original unit with BMW part number, old Behr part number, and date of manufacture. Plus of course the new version w/ new Behr number and date stamp. BMW p/n has remained the same 64116920365.

http://i1125.photobucket.com/albums/l584/aurelius3/Random%20BMW%20Pics/91fdd045.jpg

[llll1l1ll]

Saweeeet. I'll order wunna dem tings taday.

[Dave1027]

I'd be curious to see what's inside that thing. I once had a Nissan where a module failed like this causing the entire dash to go dead. I opened it up and found a 50 cent voltage regualtor inside. The dealer wanted $35 for a new module. I replace the 50cent VR and it work for good.

Leads me to think this FSR may have a cheap resistor network inside that burns up or melts the solder connections.

[llll1l1ll]

Well, when I pull my old one out, I'll see about ripping it apart!

[derbo]

IMO, jumping the gun to the FSR when you arent experiencing the final stage symptoms is just throwing parts at the problem hoping it works.

If you have access to a multimeter with amp function, you can do a test in a garage or somewhere you can leave the car with the trunk open. (windows of the doors can go down too, in case you need to do step 7.

Ammeter should at least have a 10A fuse and be able to read in mA.

1. Remove the negative terminal off the battery.
2. connect the ammeter to the cable and the other side to the battery
3. lock the trunk latch while its open so you can see if the car sleeps. (You can push it up with the supplied screwdriver)
4. Don't touch the car and leave all doors close and let the car sleep for 20minutes.
5. The amperage should be less that 80mA
6. If it isn't, wait a little longer to verify the car is sleeping and the electronics all have shut down. Another 5-10minutes should be okay.(Opening your doors will reset the timer!)
7. If it indeed is too high, this is where you go to your fusebox and start removing fuses 1 by 1 to see which system is the culprit.
8. Hopefully you find out which system is draining your system and you can further diagnose from the results.


I dont remember what fuse the final stage is part of, but I beleive it's part of the HVAC system so I would start pulling those fuses 1 by 1 since thats your starting point.

I would hate to waste $50 on a FSR if the one inside is perfectly good.

[Dave1027]

Hey Derbo, that's what I said. But you went into much better detail.

[derbo]

Hey Derbo, that's what I said. But you went into much better detail.

Sorry, I must've missed it when I was scrolling down. I agree with you though! :)

[llll1l1ll]

Ah so that's how you find the culprit. I can try to see if I can find a cheap multimeter to buy and check this out. The hardest part sounds like trying to reach in the passenger window and pull out the fuses.

I'm confident it's likely the FSR, but it could also be the radio maybe. I don't know. I'm very tired of parking my car on a hill at night.