XSeries-forum

I had a similar issue that almost drove me to despair, eventually pulled all the fuses in the front/back and over a week or so, slowly readded them until I found the offending circuit or close enough. The problem was one of the first 4 fuses in back and related to the phone, head unit, etc.  Never did fix the issue, just add the fuses when I want some tunes (lazy option).

Jump started it today and long drive. On return I measured the battery voltage with engine running=14.22Vdc, so alternator good and charging. Hooked a multimeter between batt negative(all doors shut etc) and get 3.6 amps draw, should be 750ma. Started pulling fuses and fuse 75(sat nav) and drops to 750ma . Put back in and up to 3.6 amps.  But will drop to 750ma then  360ma after a few minutes.  With all fuses in after a few minutes it's 750ma then 360ma draw, after 16 mins it goes to sleep,  drawing 40ma,  should be apprix 18ma.  But not a massive draw.

As soon as fuse 75 goes back in, car wakes up and 3.6amp draw, sat nav disc spins up, red light on, but after about 2 minutes it shuts down and current draw drops. With fuse 75 out and battery connected the whole display is inoperative and radio is on.

Should the nav unit draw this much initially?

I will monitor batt voltage after 5 hours.

3.6A is not unreasonable as that will be the drive and computer (all in the same box) running.  As long as it shuts down then it's fine.  40mA is about right.  They should draw less than 80mA in 'sleep', so your reading is well within that.

If it keeps 'waking' then the Nav computer will spin up and that's 3.6A for a few minutes every time.

It seems as if something is waking the car up intermittently and it is that causing the battery to go flat.  The alternator voltage is where it should be as you say.  It is now a case of finding the 'something' waking the car, and that is the hard part 

The lights coming on is a puzzle though.  That definitely isn't normal and is controlled by the Light Control Module.

When the car is charged, is there any indication of an unhappy starter motor?  Sounding sluggish?

Thanks for the reply.  I read it should be 18ma,  but the battery should be able to cope with 40ma. The left light coming on twice had baffled, but BMW do odd things when low volts, took the car out yesterday for a two hour drive and seemed ok.since i replaced the fsr I haven't taken it for a long drive,  so I'm thinking the fsr may have cured the drain as I'm happy with 40ma and i havent charged the battery properly. 24hrs  since last driven it's reading 12.42v. Planning a 150 mile motorway journey tomorrow,  which should fully charge it.


Here's hoping

Not checked how much ccurrent the starter is drawing, but not sluggish at all