drain on battery when off (bmw)

[VaSteve]

I put a new battery in my bmw a few months ago. When it sits for a couple days I would have hard starts. I must have had a new bad battery or some drain on the system.

Any guesses?

I ponder this while sitting in the dulles parking garage after a week out of town. At midnight.

[Dr K]

I'm visiting my Mom. If you're still there Sunday afternoon, give me a call and I'll come pick you up.

[Vicegrip]

Turn everything you can off and then hook up an amp meter to the battery line. If there is an amp draw pull one fuse at a time until the draw drops out to find it.

Battery test with home shop testing equipment. Ham-fisted shade tree wrench not perfect method. Charge battery, disconnect it from the charger and let it sit for a few hours to equalize a bit. Drop it back in the car, hook it up and turn on the headlights for 3 min to pull off any surface charge. Test and record the voltage both with the headlights on and off. Disconnect the battery and let it set for a day or 3. Test again with the lights on and off. Any notable drop in voltage after a few days is bad.

[Jase007]

Steve:

Known problem on the E39s is the heater FSU (final stage unit) that fails and keeps the small fan (in the heater control unit face plate) that samples the internal cabin temperature on even when car is off (kills the battery).

Here is an E46 thread (http://forum.e46fanatics.com/showthread.php?t=828450) on the FSU (FSR) replacement and what it looks like from e46 fanatics.

Not sure of the E46 hvac setup but a quick review of what I found on e46 fanatics seems to point to similar setup.

[VaSteve]

Jase, interesting. Exactly the kind of thing I was looking for. I'm thinking it might be a bad battery, since I got 6 trouble free years out of the one from Germany. I can't imagine things would suddenly fail in concert with a new one. I'm going to return this to Sears and go from there.

The jump truck hooked up the pack and it started on the first crank. I was getting 13.6V when I pulled in my garage last night.

I'll update this if the new battery doesn't help.

Ironically, I was considering taking the 911 to the airport but didn't want to deal with a problem at midnight when I got off the plane. Go figure.

[VaSteve]

Hmnmmf.

Sears wouldn't just swap it out. They put it on their tester/charger and the machine said it checked out "good". Maybe I left a light on? Maybe the alternator isn't charging? I can't figure how I could get to the airport OK, and when jumped make it home...to me that means the the alternator has to be good, right? I still need to get it tested.

Unless it's that thing Jase pointed out, I haven't touched the wiring on this car....

I have a road trip to Parkersburg, WV this week, I need to sort it out.

[HoodPin]

If the alternator is going bad, an in-dash voltmeter will show dropping voltage if the battery's not getting a charge.

[tdatk]

If the alternator is going bad, an in-dash voltmeter will show dropping voltage if the battery's not getting a charge.
Nice avitar Tony. I just had my battery go bad on the pickup, it was fine on Monday and toast by Thursday. Put it on a load tester and it when it was charged and it showed fine, but, it had fracture in one of the cell cluster plates and failed while I was at work. Cracked posts or plates internally are common failures although yours sound more like a slow drain.

[Jase007]

On the boards there are instructions on how to unlock your on board computer/instrument cluster so that you can monitor voltage while driving the car around.

I know the instructions for the "high" and "low" E39 cluster, there are similar ones for the E46.

Monitor voltage when you are driving to see if VR is capping it at 14.3v or whatever. If it is, and this is the normal v, then you are back to the battery drain problem, not the alternator/charge side.

[VaSteve]

Yeah, I had it "tested" at the Sears. All they did was hook up a DVM, like I did. E46 dash isn't as high tech ... I'll have to look for those instructions. I have one of those gadgets that plugs into the cigarete lighter. Good tip on that FSU/FSR, I did a lot of reading on e46 fanatics. Looks to be a common trouble spot.

[Clarke]

I'm late to the party, but Jase mentioned the #1 drain on BMWs. Unplug the blower final stage and see what happens.

[Dr K]

Steve,
So you don't need a ride home tomorrow, right?

[VaSteve]

Yes, Dr K. I'm still stranded at the airport like Tom Hanks. Garage #2.

[VaSteve]

Clarke....if I disconnect it, I can still drive around right?

[Clarke]

Yeah you can still drive, you just will not have any blower operation.

[Jase007]

Steve: Only replace with one from the dealer (Behr is MFG. I believe). Same with camshaft position sensors (intake and exhaust).

There seems to have been a boatload of crappy copies on the market for blower FSU and intake/exhaust CPSs ... many new "replacements" from aftermarket have failed.

[OldTee]

Do all this but think grounds.

If you have a small draw the loss from the battery can be magnified by a bad ground or resistance in the ground circuit, like corrosion on the battery terminals. Note said terminals.

Think about it this way. A voltage demand (12V or whatever) creates a need for current to flow from the battery. Incresed resistance increases the amount of current that needs to flow for that voltage.

Yeah, I know you know.

:)

ARF