894Re: [bmw e28] Central-locking/flat battery?
- Aug 14, 2002Tom .
By experience all BMW central locking operates on a Negative pulse.
Which means the system is constantly live and triggered by the earth.
On the E28 if I'm not mistaken the control unit is in the fuse box.
If you have a doggy wire earthing where it shouldn't this will effect the
make it work over time and run down the battery.
I would start by making sure all your connections are clean and check the
of your wires as far as you can. Wires will wear especially on the door
Get your door panels off as well. The main control will be in the drivers
If you feel down you'll see a group of rubber connectors. Water can easily
if there laying right at the bottom.
If that's all clear I'd trace the wires by colour and make sure you have
current in both + & -. (Use a Bulb tester)
You may have to replace the module in the fuse box. This will be trial &
error as it might not be the fault. New one's are not cheep, but a re-con or
a second had one
can be picked up relatively cheep.
The system is really simple, I'm sure you'll find the culprit.
PS: One last thing, get a Multi meter, put it across the battery terminals.
It should read between 11.5 & 12V. Take the fuse out of the Central locking
If the meter moves up, start tracing back to find out why. Watch out for
things on that circuit that may effect your reading as your C/Locking and
problem might not be linked.