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From digest.v9.n21 Tue Aug 4 07:14:49 1998
From: Jim Cash <>
Date: Mon, 03 Aug 1998 17:31:33 -0400
Subject: Re: Electrical Gremlins....

Geoff Bodin writes:

> I've got a 1984 E28 528i (UK Spec), and am getting some electrical
> gremlins.
> The check control system in the roof is not functioning correctly,
> although the brake LED (stop light) comes on and works fine the test button
> no longer lights the other LED's up. And the orange warning light in the
> centre of the dash is constantly flashing. Unplugging the Check control
> panel stops the centre lights from flashing.


Most likely the "Test" button (which also acknowledges any fault) is no longer making contact.
I suspect that the back of the back cover of the case has started to separate from the case body 9they are held together by plastic tabs. If the unit is not tightly closed the test switch (on the circuit board) gets pushed back too far for the button to operate it. I found this out after opening mine and then resealing it by melting the plastic tabs to hold it shut - well one of the melts broke open after a while and I had the same situation you describe. Perhaps someone has opened yours in the past.

Make sure yours is fully closed (back on tight) - failing that, open it up and test to see if the switch is actually able to operate - may have to short it to see if the switch itself is failing internally.

> The second problem is to do with the central locking system I have
> read Jim Conforti's trouble shooting guide in one of the FAQ's and this
> should help me track down the problem... Initially when I re-fitted the new
> battery everything worked fine. But now nothing works with the Central
> locking. Using the key in either drivers, passengers doors or boot no longer
> activates the CL system to lock or unlock. I was wondering if there is a cut
> out switch built into the system that might need re-setting? Also where
> about on the car is the CL control box?

The Locking control unit is in the right kick panel - behind the stereo speaker (at least it is in left hand drive cars - yours may be opposite).

Following is a functional write up I have supplied to the board before.

FIRST you should be aware of the "CAUTION" notes that are on the drawings:
  • Disconnect Battery before moving or removing the locking module. If power is applied to the control unit when it is not properly positioned the unit will be damaged. ( I think this is due to the "inertia sensor switch" which senses and impact or roll over)
  • Do not operate the system more than 8 times in quick sussession to prevent overheating of the control unit.

Here is how the 1982, and I assume other year's, systems function.

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 key lock.

Each actuator is actually a double unit.

  • - the internal "request" contacts that send ground to the control

    unit on the "lock request" and "unlock request" leads.

  • - the solenoid (motor) which actually moves the locks electrically.

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.

Contacts & Leads each door actuator are as follows:

  1. - BU - solenoid motor - LOCK SIGNAL from control unit
  2. - WT - solenoid motor - UNLOCK " " " "
  3. - YL/BU - Lock request switch - sends ground to control contact #7
  4. - GN/BU - Unlock request switch - " " " " " #6
  5. - RD/BK - shown "unused" on mine but I think it goes to alarm circuit.
  6. - BR - request switch - ground connection.

The trunk is the same except that the function of contacts 3 & 4 are reversed (this might be a typo).

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.

Contacts and Leads on the Control Module are as follows:

Connector Pin - Wire colour - Lead Function

  1. - .75 BU - "LOCK" signal to all 6 lock actuators (includes fuel door).
  2. - .75 WT - "UNLOCK" signal to all 6 lock actuators. The relay feeding these just reverses the battery and ground to the actuators dependingon whether they should lock or unlock. (current sensing will cutout if an actuator runs for more than 35 seconds).
  3. - 1.5 RD/WT - Power - hot at all times.
  4. - .75 BR - ground
  5. - .75 GN - Power to inerita switch (closes at impact of 5 G) to unlock car)
  6. - .75 GN/BU - UNLOCK REQUEST from front doors (actuators).
  7. - .75 YL/BU - LOCK REQUEST " " " "
  8. - .75 GN/BK - LOCK REQUEST from trunk actuator.
  9. - .75 YL/BK - UNLOCK REQUEST " " "
  10. - .75 RD/BU - DS Lead (may not be used) For security system.
  11. - .75 RD/YL - DWA Lead (" " " " ) Security Siren

The control unit also has an internal "automatic unlock" switch that initiates an unlock request should it sense an "impact" greater than 5g. This is what unlocks 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.

If you are having intermittant problems with your locks, here are some things to

Fuse # 5 - make sure it is tight and not corroded.

If you can not lock/unlock it from the drivers door, try the passenger door. If that works then I would suspect the actuator in the driver's door. Both these actuators are wired in parallel.

If neither of those work, then try the trunk unit - it connects to the Central locking unit on different contacts (8 & 9). If that works then I would suspect the actuator in the passenger door, or it could still be the drivers door. A clue could also be do you remember one of these operating more slowely than the others. In cold weather my locks would sometimes quit, but I could always get in using the trunk unit.

The actuators are held together with pop rivits. If it turns out that you think it is an actuator (if you unplug one and the problem does not occur - i.e. all the others work) then rather than buying a new one I would attempt to take it apart.

Although I no longer have on to verify my assumptions I would do this.

  • Drill out the rivits and open the unit.
  • clean the contacts and ensure they can operate freely.
  • spray inside with WD40 and reassemble. (use some small screws & nuts etc to replace the rivits - sometimes sheet metal screws will work as well.
  • check that you have electrical contact, or plug in and test before putting door back together.

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.

Regarding your clock
> About the same time as this stopeed working the clock on the dash stopped
> giving any sort of read out... It just glows amber but has none of the
> digits lit.
If it glows amber when the dash lights are on - that means you probably have lost power to the clock unit itself - ot the clock unit is "dead". Need to pulll it out and check if you have power and ground. Ground should be a brown wire and there shoudl be power on the others (I think the dash light power is on the gray/red wire.) If you have all that - clock dead ! If you are any good a checking for faults on the internal circuit board go ahead, otherwise try thumping it (can't hurt at that point).

Hope all this helps.


Jim Cash
London Ontario, Canada
E39 540ia

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