E30/E28 central locking FAQ
This FAQ covers central locking on E30 (3 series '84-'91) and
E28 (5 series '82-'88) cars.
It also seems to apply to E24 (6 series '76-'89) and maybe others (?)
2.0 Functional Overview
3.0 Common Problems and how to fix them
Lock system/ production years/ models
Central locking was standard, but early models (<'85) do not have the
double-lock feature. Starting somewhere in 1985 model year, the double
lock feature became standard. Actually, it seems that the double lock
feature was used in all E30's with production date 9/84 and up. E28's
seemed to start 1/85 or mid year production.
Early models had keys marked with an 'I' and where shorter, using a 4
digit key code. Later models are marked with an 'S' and have longer
keys with a 5 digit key code. The double-lock feature is engaged with
the last section of the key - the valet key is shorter than the
regular keys and does not engage the double lock.
2.0 Functional Overview ( by Paul Reitz prreitz_at_amp.com BMW CCA #1167)
The system allows the entire car to be locked from either front door key
lock, the trunk key lock, or by depressing the driver's door lock button
inside the car. It also allows the car to be double-locked (from the
driver's side key lock) so an intruder cannot unlock the car just by
breaking a window or using a tool to lift one of the door lock buttons. If
the car is locked - but not double-locked - it can be unlocked via the key
lock from either front door or the trunk, or by lifting either front door
lock button from the inside. The doors automatically unlock via an inertia
switch that operates on impact greater than 5g. Door lock buttons on 4
door models have no control over central locking, although they can lock,
and under certain circumstances unlock that particular door. Never
double-lock a car with occupants inside!
The system consists of the following components:
Key lock cylinders in each front door (and the trunk), which operate the
door latches that prevent the door handles from operating, and
which in turn
^^^^^^^^^^^^ have mechanical linkages to the
door lock button and to the
door lock motor unit mounted inside the door cavity. (There is also a
trunk lid lock
^^^^^^^^^^^^^^^^^^^^ motor unit that locks the trunk latch button, and a
gas filler lock
motor.) Most door lock motor units have two motors: =
door lock motor, which operates the door latch locking mechanism and
door lock button, and the
double-lock motor, which "pins" the mechanical linkages and the door
latch so they
^^^^^^^^^^^^^^^^^ cannot be manually unlocked. The driver's door
and trunk lack the
double-lock motor; the trunk doesn't need one,
since there's no
"lock button" there, and the driver's door is
double-locked by the
mechanical constraint of the 90 degree position of
the key lock
cylinder. The door lock motor unit also contains th=
lock and unlock switches which send "lock" and "unlock" signals to the
Central Lock Control Unit (CLCU). The CLCU contains some electronics and th=
LOCK and UNLOCK relays, each of which has a set of normally-open and
^^^^^^^^^^^^^^^ normally-closed contacts with a common connection,
operate all door motors. The CLCU is located
behind the speaker in
the left front kick panel.
In addition, there are
microswitches mounted on the front door key lock cylinders. On
^^^^^^^^^^^^^ door, this is the "unlock inhibit" microswitch,
which closes only
when the key lock cylinder is rotated to the 90
and initiates double-locking. A similarly
in the front passenger's door is operated at the 45
position, but is used for unlocking only.
Locking and Unlocking:
When a door or trunk key lock is turned 45 degrees, or the driver's door
lock button is depressed, linkages move to close a "Lock" switch contact in
the respective door lock motor unit. This contact grounds the Lock input
on the CLCU, which, if the car is presently unlocked, momentarily energizes
the "LOCK" relay. This relay has a normally closed (NC) contact and a
normally open (NO) contact, with a common connection. (Technically, an
SPDT relay.) The common is wired to one side of all door lock and
double-lock motors; the NC contact goes to ground, and the NO contact goes
to +12 volts via fuse #27. When the relay operates, current flows through
the (now closed) NO contact, through the door lock motors to ground through
the other, unenergized relay's (still closed) NC contact. The motors run
to a physical limit and stall; the relay is de-energized after about 1
second, and current flow ceases.
Unlocking operates analogously, via "Unlock" switches and the UNLOCK relay.
The manner of operation of the Lock and Unlock relays is to just reverse
the polarity of power applied to the door lock and double-lock motors,
except that the UNLOCK relay contact common is not wired directly to the
double-lock motors. Only one relay operates at a time.
One side of all door lock and double-lock motors is connected to the LOCK
relay common, but the other connection of the double-lock motors is to pin
11 of the CLCU, which is at the junction of two "steering" diodes. One of
these diodes is connected to the "unlock inhibit" input (pin 10 of the
CLCU), and provides a ground return for the double-lock motors only when
the driver's door microswitch has been closed (by turning the key lock to
Although the passenger's door lock motor unit contains both "lock" and
"unlock" contacts, only the "lock" contact is connected. This allows the
passenger to lock the entire car from the inside, but not to unlock it.
Unlocking from the passenger's side can only be done by closing the
microswitch in the passenger's door with the key, from outside the vehicle.
If the car is double-locked, the passengers' door double-lock motor
prevents the key lock from being rotated so the car can only be unlocked
from the driver's door.
The front passenger (and any rear door) door lock motor units contain a
double-lock motor. When it is activated, it mechanically locks the
linkages themselves, preventing the door lock buttons from being lifted,
thus making unauthorized entry more difficult.
When the driver's door key lock is first rotated to 45 degrees and the
"Lock" relay operates, 12 volts is applied to the double-lock motors via
the LOCK relay common, but the other double-lock motor connection via the
diode junction offers no return path to ground, so the double-lock motors
do not operate. When the driver's door lock key is turned to 90 degrees,
it closes the "unlock inhibit" microswitch, which grounds the "unlock
inhibit request input", CLCU pin 10. Now, a complete return path is
created from the double-lock motors to ground via pin 11, through the diode
to pin 10, through the (closed) unlock inhibit microswitch. The closure to
ground of the microswitch also signals the "unlock inhibit request", which
operates the "LOCK" relay. This time, because of the ground return through
the steering diode, the double-lock motors also operate, and the door lock
linkages are latched in the locked position.
The driver's door itself does not have a double-lock motor; removing the
door key in the 90 degree position jams that door's latch (and lock
button), serving the same function. The grounded unlock inhibit
microswitch prevents the trunk key lock from creating an unlock event.
Unlocking a double-locked car:
This action can only be initiated from the driver's door key lock. When
the key is rotated CCW from its double-locked position, it releases the
ground connection of the unlock inhibit microswitch. (Actually, once this
is done, the trunk key lock can also be used to unlock the car.) As the key
is rotated another =89 90=B0 CCW, it mechanically unlocks the door latch,
raises the door lock button and moves the door lock linkage to a position
that closes an unlock switch. The "UNLOCK" relay operates, and unlocks all
doors. (During any UNLOCK relay operation, 12 volts is also applied to
the second steering diode, which allows the double-lock motors to operate.)
The current return path to ground from all lock and double-lock motors is
via their connection to the (unenergized) LOCK relay NC contact to ground.
The double lock motors operate quickly enough to also allow the door lock
motors to operate.
3.0 Common Problems
3.1 Drivers Side Door lock cylinder
A common problem is that the door lock cylinder does not turn
properly. It either can't turn past 45 degrees ( all the way to 90
degrees clockwise to engage double lock ) or it won't turn back and
unlock the door properly.
Also, various parts of the lock cylinder mechanism crack, fall apart,
bend, and springs get too weak.
Remember, the drivers door should LOCK completely mechanically (ie you
can disconnect the battery and check this out) by turning the key 45
degrees to the right.
If it doesn't quite lock, or takes a few tries to get the lock button
to go down completely, then the lock cylinder probably needs
If you also can't turn the key past 45 degrees, it probably means the
lock cylinder needs replacing.
BMW has something called "Door Lock w/key repair kit" or something
like that, BMW part number 51211924903 or maybe 51-21-9-061-343.
Both have been reported as correct so who knows? Anyway, it should
cost around $30 (us) from a dealer. It comes with a new lock cylinder,
and all possible tumbler combinations so you can key it to your
existing key. I have included the translated german instructions at
the end of the FAQ.
3.2 Intermittent locks, non-working central locking, buzzing from the
Check the connector from the drivers door to the A pillar. Pull back
the rubber boot and pull apart the connector. It is often full of
corrosion and the pins no longer make contact.
Pins and sockets are available from BMW ($0.50 each?) or possibly from
your local electronics store. They are the same pins and sockets as in
AMP CPC connectors.
Pull out the corroded pins, cut and solder on new ones and put back in
Pin-out for the sockets are at the end of this FAQ.
3.3 Burnt out door lock actuator motors
Test to see if the +12v and -12v signals are getting to the door lock
actuator motor. If so and the motor doesn't move, replace. Note that
drivers door is different than passenger side door is different than
trunk and gas latch.
housing --> upper lower
drivers door White Red
passenger Red Red
rear doors Red White
Trunk White Red
3.4 Central locking works but unlocks a second or two later.
If you lock the doors and they unlock again almost immediately it is
because there is a problem. A motor is dead or something is
jammed. The central locking is telling you that everything is not
Find out if all motors work, make sure there are no bent rods or
things jamming the mechanism.
4.0 Getting inside a door and removing the door lock cylinder
remove arm rest ( 2 screws )
remove power mirror control (pull out) and remove screw in behind
remove door lock button
remove door latch trim piece (push to the right or left and it should
pull panel away from door sides and bottom. I use my fingers. It will pop
out plastic snaps. Lift panel up to detach lip from top of door.
peel back sticky plastic barrier
now, a 2 door has much more room inside than a 4 door.
either way, if you remove the bottom nut on the window channel you can
move the channel around to get it out of the way.
Outside the door undo the screws holding the handle on.
Inside the door undo the two bolts holding the handle mechanism to the
door. Wiggle and swear until you remove the mechanism.
You then have free access to the door lock cylinder. There is a 'clip'
which pulls off to the right. Once that is off, the cylinder can be
removed from outside of the door.
Many people have then found that the cylinder mechanism has
- a bent arm - they bent it straight and it worked fine after that
- a cracked arm - replace cylinder assembly
- weak springs (put key in and try out the mechanism)
- something else broken.
You can also check your latch mechanism still inside the door - it
should work freely with no binding.
4.0 Related Accessories
BMW Factory alarm consists of hood sensor, trunk sensor, door sensors,
ultrasonic motion sensor. It arms when the double lock is
activated. It includes an ignition kill, flashes the lights, and honks
the horn when triggered.
4.2 Door lock heater
Often disconnected, broken, or stuck in the 'on' position leading to
possible fire. When pulling up on drivers side door latch, a ground
connection is made at the heater module. This signals the central
locking to send 12V to a resistor mounted in the clip holding the lock
cylinder to the car. To operate: lift and hold latch.
4.3 Interior light with delay
Mounted in place of door lock heater. When handle is lifted for entry
to car, a timer is set to keep interior lights on for a short amount
5.0 Door Lock Repair Kit Instructions
Remove door lock cylinder as previously described.
BMW instructions are as follows:
Before assembling, fill the lock channels of the key cylinder with the
Insert the lock and the lock springs corresponding to the code list or
the key in question.
Build the lock cylinder according to the drawing.
To make assembly easier, grease the roller and the accompanying 'N'.
Lead the 'N' into the leading ring.
Pay attention to the lock in the cylinder.
Carefully with light hammer blows, lead it in.
Put the dead-point-spring in place and tighten.
6.0 Central locking troubleshooting guide (by Jim Conforti)
Start with doors unlocked and all windows open
NOTE: NEVER CONNECT OR DISCONNECT THE CONTROL UNIT UNLESS BATTERY POWER IS
Operation Response Action
1 DDL to lock All doors lock Goto OP #2
Some doors Lock R/R suspect Door Lock Motor ckt.
No doors Lock Goto OP #4
2. DDL to deadbolt All doors double lock Goto OP #3
Drivers and SOME others dbl lock R/R suspect Door Lock Motor
Drivers ONLY dbl locks Perform TEST B
Drivers does NOT dbl lock Mechanical Problem
3. DDL to unlock All doors unlock Goto OP #4
Some doors unlock R/R suspect Door Lock Motor ckt.
No doors unlock Goto OP #5
4. PDL to lock All doors lock If doors did not lock in OP #1 R/R
DD lock switch
else Goto OP #5
Some doors lock R/R suspect Door Lock Motor ckt
No doors lock If doors locked in OP #1 R/R PD microswitch
if doors did not lock in OP #1 perform TEST A
5. PDL to lock All doors unlock If doors did not unlock in
OP #3 R/R DD lock switch
else Goto OP #6
Some doors unlock R/R suspect Door Lock Motor No doors unlock If
doors unlocked in OP #3 R/R PD Lock Switch
if doors did not unlock in OP #3 perform TEST C
6. Get in car, close/lock all Doors remain locked Goto OP #7
doors, IGN to RUN Doors Unlock R/R Central Locking control unit
7. Get out, DDL to lock All doors can be unlocked Goto OP #8
Unlock each door by All doors remain secure Disconnect connector from
control unit and check
pulling up button for short to ground at terminal #11
if short, find it!, if not R/R Control Unit
8. Trunk lock to LOCK Trunk Locks Goto OP #9
Trunk does not lock If doors lock, R/R Trunk lock motor and/or circuit
If doors do not lock R/R Trunck lock switch
R/R Control Unit if switch and circuit are OK
9. Trunk lock to UNLOCK Trunk unlocks Goto OP #10
Trunk does not unlock If doors unlock, R/R Trunk lock motor and/or circuit
If doors do not unlock, R/R Trunk lock switch
R/R Control Unit if switch and circuit are OK
10. Turn key back to LOCK Gas filler locks Goto OP #11
Gas filler does not lock R/R Gas Filler Motor ckt.
11. Turn key to unlock Gas filler unlocks Done, No faults!
Gas filler does not unlock R/R Gas Filler Motor ckt.
Measure Voltage at Control Unit Connector w/ Control Unit Connected
Term 3 and Ground should be battery, else check wire to Term 3 for open
Term 3 & 4 should be battery, else check wire from Term 4 for open to
Jumper between Term 7 and ground, if doors lock R/R switches and related
wiring else ...
Disc. battery, remove Control Unit and reconnect Batt. jumper 1 & 3
together, now jumper 2 & 4 together if doors lock, R/R Control unit, else
check wires on Term. 1 & 3 for opens (see schematic)
With Conrol Unit connected, jumper between 10 & ground doors should double
lock, if not, check wires to Term. 11 for opens and R/R Control Unit if no
opens found. If doors DO double lock, check wires to Term 10 for open and
R/R Unlock Inhibit Switch if wire OK.
With Control Unit connected, Jumper 6 & ground. If doors unlock, R/R
switches and related wiring (see schematic) if doors do NOT unlock R/R
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