Electrical gremlins after flat battery (E39 540i)

[AllenN]

I opened the boot/trunk lid a week ago Sunday and the alarm sounded. Neither pressing the remote key buttons nor turning the ignition to Position 1 would stop it. I think I finally slammed the boot lid down and slammed the garage door after it in a state of desperation. When it finally went quiet I re-entered and checked the voltage at the battery charging points under the bonnet/hood: 5.5 V. I figured I must have left my custom Hi-Fi on the night before, draining the battery. I then connected a charger to the charge points and plugged it in: 8 A it showed. Then the alarm sounded again!!!

At this point I switched off the charger and went away to think. I concluded that the only way to charge the battery without the #*%& alarm melting my brain was to disconnect the battery earth leads and charge the battery directly. So, come Monday morning, I had a car again... mostly.

The first problem I noticed was that the LED status/warning thingy was dark, whereas previously it had been warning me about the remote key battery (which I had just changed already!) and a tail light (which was dark but is now okay again !?!?).

Then I found that neither the remote key button nor the under-dash button would open the boot/trunk; I have to insert the key and turn hard anti-clockwise to open it. I happened to have a spare latch/actuator assy, so I installed it: no good. (The light inside the boot/trunk lid still works, so that bit of wiring clearly still gets power.)

Tonight, I discovered that using the key in the driver's door lock (i.e. turn anti-clockwise and hold) locks the doors okay but no longer closes the sunroof.

So now I'm wondering: are all these things on the same fuse, or is there something more nefarious going on?

(Nb. I used to own a Triumph, and sometimes I wonder if the old Lucas engineers went to work for BMW when British Leyland went bust!)

[DennisCooper]

Hi

Search the E39 sub section as this is the one for car audio and associated electronics. You might have a faulty ignition switch, a failed or failing module, possibly chafed wires, a weak battery that needs replacing etc.

Good luck

Cheers, Dennis!

[AllenN]

Thanks, Dennis.

I was thinking alarm/security/electronics and seized on this forum, but I'll go to the E39.