E30 / E28 central locking FAQ

Prepared by Christopher A. Pawlowicz (

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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 other.

1.0 Introduction

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)

1.0 Introduction

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 BMW CCA #1167)

Intended Operation

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 kick panel.

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 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 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 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

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 CPC connectors.

Pull out the corroded pins, cut and solder on new ones and put back in the connector.

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 latch.

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 pop off)

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 time.


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 enclosed lubricant.

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


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 Control 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

Control Unit.


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