Adie84

Hi,

I have a 2003 545i (only had it since Xmas eve) with which I am experiencing a high battery drain issue. To diagnose this I am going to connect my ammeter in series with the negative terminal on the battery then pull fuses until I find the item causing the drain.
If I disconnect the battery will I be prompted to input any information, as I have checked the documents I got when I bought the car and it doesn't have anything specific to the car like a radio code etc?
Apologies if this is a daft question but I have never had a BMW before and the more I read, the more I find everything appears to be tied into the iDrive.

Cheers, Ade

BimmerFan52

Congratulations on your car. Your question is a good question (we don't take off points for newbie questions).

Usually the only thing you will have to reset is the clock, and maybe some radio station presets or seat memory presets.

When measuring for parasitic current, the closed circuit current spec is around 40mA.

One thing you might first try is to disconnect the IBS (Intelligent Battery Sensor) which is part of the negative battery cable, and is a problem with early E60s. It is a small microprocessor that constantly measures battery voltage, current coming into the battery and leaving the battery, and the acid temperature of the battery in order to help the ECM (main car computer) understand the battery's general state of charge. Depending upon the battery state of charge the ECM can tell the alternator to increase or decrease current to the electrical system, with the effect of raising or lowering the system voltage to accelerate battery charging.

One of the tasks of the IBS is to wake up the ECM (which normally goes to sleep once the car has been turned off to conserve battery power). If the car were turned off, but the key was left in the on position with the radio, seat heater, etc. left running, then after a period of time the IBS senses the battery is being drained quickly, and can wake up the ECM which will turn off a relay to interrupt power to these "non-critical devices". After this event the ECM is designed to go back to sleep.

A properly operating IBS will only wake the ECM once. But early versions of the IBS were improperly designed and allow moisture to damage the unit, sometimes causing it to malfunction and repeatedly wake up the ECM and drain the battery.

From the negative battery cable you will see a small wire with a blue plastic terminal on the end. Disconnecting this wire (the communication line between the IBS and ECM) will prevent the IBS from waking the ECM. It will not hurt the battery or prevent it from being charged.

After disconnecting the IBS make sure the battery is fully charged and then wait. If the battery stays charged then your IBS is the source of parasitic discharge. If not then good luck on your continued hunt!

Cheers Mate!

Adie84

Thanks for the detailed reply, much appreciated.
I have had the IBS sensor disconnected now for over a week (although I unplugged the red power lead to it from the positive terminal, would this have the same effect as the lead you describe?) and thought the car had a bit of a problem starting this morning (however it did actually start it just didn't seem normal, hard to explain).
So I decided I was going to see if I could find anything obvious this afternoon and connected my ammeter, closed door and boot latches and waited for the car to go to sleep.
When it went to sleep the current dropped down to about 210mA. I removed the fuse for the CD changer but there was no change. Next, interior lights and central locking, still no change, so I plugged them back in.
When I plugged the fuse back in for the central locking it woke the car up so I had to wait 15 minutes again for it to go to sleep. This time it dropped right down to 20-30mA and stayed that way for half an hour. I gave up after that and decided to call it a day, but I don't understand how it was drawing 210mA the first time it went to sleep then significantly less the second time yet I had the same fuses connected.

Adie84

Hi Bimmerfan52,

Is this the lead you are referring to in your post?



This is the socket which is cable-tied onto the negative lead that I unplugged the IBS power lead from so I'm guessing I need to plug this back in and unplug the one above if that is the correct one:



Thanks again.

BimmerFan52

Is this the lead you are referring to in your post?
Yes, unplug this one with the blue connectors - That is the BSD or Bit Serial Data interface that the IBS uses to communicate with the ECM.


This is the socket which is cable-tied onto the negative lead that I unplugged the IBS power lead from so I'm guessing I need to plug this back in and unplug the one above if that is the correct one:
Plug this one back in. It is the B+ Terminal lead, which is a positive lead that the IBS uses to measure the system voltage. It really doesn't matter if it is unplugged while the BSD is unplugged as the voltage may be measured but it will go uncommunicated anyway.

Adie84

OK will do. Thanks again.

Redtwin

FWIW, my car takes longer than 15 minutes to go to sleep. The start button and the rear window lock indicator switch off after 15, but the gear indicator next to the shifter stays illuminated much longer. Over 25 minutes last time I tried watching it.

When you first measured 210ma it may not have been fully asleep and the second time with the lower reading, it was.

Adie84

Yeah that's probably it. Thanks for the info.

Adie84

I have now done this. I'll see how I get on for a few weeks. Cheers.

530dE60

OP how did you get on ? Any updates ?