Huge battery drain

[John the Blind]

Hi Guys,

Any ideas welcome. Z4M runs fine for a month or so and then goes from starting well on one day to having a battery so flat that the car will not even turn over the following morning. Has happened now on 5 occasions.

Last episode was last week. The car had done 1500mile in a month. It started very strongly and did 40 miles before it was parked up last Wednesday evening. Thursday morning it would not even light the dashboard (10 hours later, 70 amp hour battery so 7 amp per hour overnight).

Only clue is that the the telephone (bluetooth) disappears off the menu a couple of days before it goes flat.

BMW are drawing a blank. Drain tests are providing no clues.

Any ideas or experience. Would be interested in any tech ideas of what would run on a Z4M with the keys out of the ignition which would draw 7 amps per hour. We obviously suspect the bluetooth unit but I am surprised it would draw that much.

Appreciated

John

[john_p]

Every single M-car I have owned in the past ~6 years has done this at some point in the car's ownership (2 M3s then a Z4).

Tracker?

[John the Blind]

Yes, BMW wondered that and so replaced it last time. Still no joy.

Thanks John

[< FORZA WEST]

Any ideas or experience. Would be interested in any tech ideas of what would run on a Z4M with the keys out of the ignition which would draw 7 amps per hour. We obviously suspect the bluetooth unit but I am surprised it would draw that much.

If there was something drawing 7amps then it would be obvious to you as basically that would be all the lights on, fan running etc.
If it was a deisel then I would suggest the glow plugs are active.
Even if Bluetooth has failed and was keeping the car awake that would only draw a max of 3.5 to 4 amps.
Easiest way to eliminate bluetooth is to unplug it.

Has the Starter motor been checked? Whats its Amp draw on the battery during start up - inparticular the time it fails..We have had issues with starters.
Also, has the earthing been tested for the battery and also the body to engine earth.

[John the Blind]

I might be a little high at the 7amp/hr. The battery appeared completely flat but apparently there was about 4v left in it. This could tie into the bluetooth unit if that can draw 3.5 to 4, thanks for the draw tech on that.

I suggested disconnecting the bluetooth but the fault is very random. BMW had the car over Christmas for 6 weeks and it did not occur. We have had it back 4 weeks and it has just gone.

Thanks for the pointers regarding earthing, I will ask them to check these but my money is nailed on the comms unit. I have posted this on BMW general and another guy had a identical fault cured by a replacement Bluetooth unit.

John

[outnumbered]

Tracker ?

I had a "mystery" battery drain on my E36, which was down to a tracker unit I had forgotten was there Previous owner had fitted it, and I never re-subscribed.

[Shadytree]

Combination of Tracker and comfort access.

Had the same issue on my E60 M5

Not fully solved yet, but I now hook it up to a trickle charger in the garage when I'm not using it. STill get the message, but not seen an problems starting since.

[mikez328]

"Trackers" draw minimal current - & they are designed to do exactly that - unless improperly fitted. Just like the factory alarm system that flashes all day/night...

I'll bet that one of your interior/boot lights is on 24/7. Put the car in a garage & have a look in the dark for any little "glows" tonight. My bet is the boot light is on all the while. It's happened to me several times over the years.

Edited by mikez328 on Wednesday 4th March 10:11

[happidec]

I went to see Phil Crouch last week due to a huge battery drain on my E36. He advised me that the boot lights were indeed on! Changed the locking device damaged by thieves and now the battery.... keeps going flat still. Need a new battery as it's taken it's toll after about 10 occasion of being disconnected charged drained and disconnected again.