From digest.v7.n742 Wed Dec 10 11:52:52 1997
From: Jim Cash <j.cash_at_sympatico.ca>
Date: Wed, 10 Dec 1997 00:54:38 -0500
Subject: Re: <E-28> Central locking woe AND consol control swtich mod
> Michael Nover writes:
> I just got a new (to me) 88 535is. It is showing the same problem my 533i
> had a few years back, but its been so long, I don't remember what I did to
> fix it. I haven't been able to find a fix in the FAQs so far.
> When I unlock the car, especially from the trunk lock, it will unlock all
> the locks, then imediately relock them on its own. I seem to remember
> possibly adjusting the thrwo of the trunk locking acctuater linkage, but as
> I said, I'm not really sure what I did on the other car to fix it.
> Any help would be greatly appreciated.
Michael - sounds like one of the other actuators is seized in the "lock
Following is something I posted a while back for someone else.
Here is how the 82, and I assume your, system functions.
The key locks are mechanical and are independent of the electric locks.
But they are physically linked at each door and the trunk so that the
actual lock mechanism is controlled by the combination of the key &
electrical actuator linked together. When you turn a key you are not
only locking/unlocking that door physically, but also moving the
actuator for that door - which then sends a lock/unlock "request" to the
control unit. The control unit then sends the appropriate lock/unlock
"signal" to all the actuators (in parallel), which use a solenoid to
produce the same movement in the locking mechanism as does the physical
Each actuator is actually a double unit.
When all actuators are in the same position (locked or unlocked) the
system is at rest. As soon as one actuator is moved (i.e. moving the
solenoid from unlocked to locked position) now a ground appears on the
lock request lead to the control unit - which reacts and sends a "lock
signal" to all actuators. If they all respond and go to their locked
position, then their associated request switches are now grounding their
"lock request" leads. Since the system is already locked, and since
there are no grounds on the unlock leads - all's well.
But if one of the actuators fails to operate, or if one of the internal
switches has failed then you immediately get a ground on the opposite
lead. Depending on the nature of the fault it might affect only the
locking, or the unlocking operation.(i.e. a switch shorted in the unlock
position will allow all the locks to unlock, but will not allow them to
lock.) If this is intermittent due to a slow acting actuator, or
corrosion in the switch, then you will get both situations, at times.
The contacts on each door actuator are as follows:
- - solenoid motor - lock signal from control unit contact #1 - blue
- - solenoid motor - unlock " " " " " #2 - white
- - request switch - lock request - sends grd to control contact #7 -
- - request switch - unlock " " " " " " " #6 -
- - shown "unused" on mine, but I think it goes to alarm circuit.
- - request switch - ground connection.
The trunk is the same except that the function of contacts 3 & 4 are
reversed (this might be a typo).
Also the wires and connections at the control unit are different as
3. - request switch - unlock request - ground to control contact #9 -
4. - request switch - lock " " " " " " #8 -
The drawing shows the lock request leads from the doors, and the trunk,
connecting together inside the control unit. While this makes sense
functionally it does not account for why you can sometimes use the trunk
unit when the doors will not work. I suspect that the drawings not
completely accurate inside the control unit.
The control unit also has and internal "automatic unlock" switch that
initiates an unlock request should it sense an "impact" greater than 5
g. This is what unlock your doors in an accident. I remember hearing
that it also reacts to a roll over - never tried it. That switch is
powered in "Run" and "Start" positions on contact #5. It is not powered
when car is off so that you can not unlock a car by running into its
bumper (impact) - yes some of the older ones work this way.
In case you are interested, I found it very useful to have a toggle
switch on the console (just below and to the right of the shifter) to
operate the locks. I just drilled through the little plate to the right
of the automatic shift - it pops out) and mounted a double throw toggle
switch. I connected the centre pole to ground and the other 2 leads were
connected to the lock & unlock request leads that go to the control
unit. You can splice into them up under the dash at various places - or
you can go right to the control unit.
Suggest you mount the switch so that pulling it back causes a lock
request. That way you can get in the habit of locking the car as you
shift into gear, and unlocking as you shift to Park.
- Do not operate the locks more than 8 times in a row to prevent
- Disconnect battery before moving/removing the the central locking
unit (in right side kick panel behind the speaker) Unit must be properly
positioned so that internal "impact" sensor works correctly.
Hope this helps.
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London, Ontario, Canada
BMW CCA 102929
E39 '97 540iA