E30 / E28 central locking FAQ
Prepared by Christopher A. Pawlowicz
(If you'd like this emailed to you via within minutes, send a blank email
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
2.0 Functional Overview
3.0 Common Problems and how to fix them
4.0 4.0 Related Accessories
5.0 Door Lock Repair Kit Instructions
6.0 Central locking troubleshooting guide (by Jim Conforti)
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 firstname.lastname@example.org 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: = the 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 the lock
and unlock switches which send "lock" and "unlock" signals
to the Central Lock Control Unit (CLCU). The CLCU contains some electronics
and the LOCK and UNLOCK relays, each of which has a set of normally-open
and normally-closed contacts with a common connection, and which operate
all door motors. The CLCU is located behind the speaker in the left front
In addition, there are microswitches mounted on the front door key lock
cylinders. On the driver's door, this is the "unlock inhibit"
microswitch, which closes only when the key lock cylinder is rotated to
the 90 degree position, and initiates double-locking. A similarly positioned
microswitch in the front passenger's door is operated at the 45 degree key
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
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 90 degrees.)
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
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
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 replacing.
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.
Intermittent locks, non-working central locking, buzzing from
the lock relays
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
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.
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
housing --> upper lower
drivers door White Red
passenger Red Red
rear doors Red White
trunk White Red
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 locking properly.
Find out if all motors work, make sure there are no bent rods or things
jamming the mechanism.
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) a bent arm - they bent it straight and it worked fine after that
b) a cracked arm - replace cylinder assembly
c) weak springs (put key in and try out the mechanism)
d) 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.
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.
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 of
Door Lock Repair Kit Instructions
Remove door lock cylinder as previously described. BMW instructions are
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.
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 REMOVED!!
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
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
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 &
together, now jumper 2 & 4 together if doors lock, R/R Control unit,
check wires on Term. 1 & 3 for opens (see schematic)
With Control Unit connected, jumper between 10 & ground doors should
lock, if not, check wires to Term. 11 for opens and R/R Control Unit
opens found. If doors DO double lock, check wires to Term 10 for open
R/R Unlock Inhibit Switch if wire OK.
With Control Unit connected, Jumper 6 & ground. If doors unlock,
switches and related wiring (see schematic) if doors do NOT unlock R/R