Central locking; sudden death of....

[andyf]

My central locking has worked perfectly for years (lucky me) until about a week ago when it all of a sudden stopped working.

All of the locks work but none of them actuate the central locking. I have pulled out the locking ECU and checked the thermal fuse which is fine and voltage tested the red/black supply which is also fine. I then used wire links in the ECU plug to test the actuator motors and all doors, boot and petrol cap lock and unlock as they should.

The circuitry of the ECU looks fine but am I right in thinking that it is now dud in view of the above?

My other thought was the micro switches and in particular the one in the drivers door; but in that case wouldn't it still be possible to operate the central locking from the boot or passenger door?

Any suggestions greatly appreciated

Andy

[Brianmoooore]

How did you test the red/black supply, and have you done the "red/black wire mod.", which should be done on all E30s, irrespective of whether you have locking problems.

[paultv]

There's also a selection of specific tests one can do to the door control ECU which will identify any problems it may have internally, listed in the BMW Electrical Manual.

I found one here:

http://wedophones.com/Manuals/BMW/

very useful

Paul

[d1mkaz]

How did you test the red/black supply, and have you done the "red/black wire mod.", which should be done on all E30s, irrespective of whether you have locking problems.

this

[andyf]

I tested the red/black supply with a volt meter to the brown wire and no I have not yet done the red/black wire mod. I assumed that as the wire links operated the locks that the power supply was there?

[Brianmoooore]

Volt meter is next to useless for such a test. The input impedance of modern digital meters is in the order of mega-ohms, so, on an unloaded circuit, it will still read 12 volts even if there is a series resistance (caused by corrosion) of hundreds of kilo-ohms. The locking will cease to work with a series resistance of only a couple of tens of ohms.
Repeat the test between the red/black and brown wires with a 12 volt bulb of at least 5W, preferably 21W, and see if it lights at full brightness.

[andyf]

Thanks Brian, will do and report back.

[andyf]

I have just repeated the test between the red/black and brown wires with a 12v bulb. Both a 5w and a 55w lit up at full brightness; I couldn't put my hands on a 21w. Does this point to a clapped out relay given that the motors are all working OK? The relay internally looks almost brand new with the exception of some corrosion on the pin that goes to the red/black wire which I have cleaned off?

[Brianmoooore]

I have just repeated the test between the red/black and brown wires with a 12v bulb. Both a 5w and a 55w lit up at full brightness;

That's a pity. If they hadn't, we'd know what's wrong and how to fix it!
You'll see two open relays inside the ECU. Plug it back in with the case off, and work the relays manually in turn. One should set the locks, and the other unlock them.
Don't push both together, and only push them for half a second.

[andyf]

Thanks again Brian, I will do that tomorrow morning and see what occurs
Andy

[ChrisHC]

I found that one of the relays in my ECU had lost its spring.

[andyf]

I was up bright and early and tested the relays in the ECU which both worked fine unlocking and locking the doors on demand. Both of the springs are OK (thanks Chris) and visually all looks good but no joy from any of the exterior locks. Very peculiar; I could understand one lock/micro switch failing but not all of them; I am clearly missing something. Any ideas Brian?

[Brianmoooore]

Have a look at the dead lock circuit. If this is permanently 'on' it could conceivably stop the rest of the locking from working. Unplug the locking ECU, and connect continuity meter/ohmmeter between the red/brown on 10 and the brown on 4. Should be short circuit with the driver's door key in the deadlock position, and open circuit with it anywhere else.

[ianev]

My fuel door mostly locks when I go to fuel up and I have to lock unlock drivers door to open it. Any thoughts?

[Brianmoooore]

My fuel door mostly locks when I go to fuel up and I have to lock unlock drivers door to open it. Any thoughts?

It's just another lock motor, connected in parallel with all the rest, so if the rest aren't locking on their own, you can rule out anything electrical.
If it isn't electrical, then it must be mechanical, so look for something that's pushing the locking pin over with the vibration of driving the car. The rubber bellows that provides water proofing is the obvious candidate, possibly 'picking up' on the rod slightly, and moving it over so that it catches the lock plate.
Unlocking the car again moves the rod back again, just enough to clear the lock plate.

[ianev]

Awesome. Thank you Brian.

[andyf]

Sincere apologies Brian for the delay in getting this test done and thanks for your help so far. I've just run the ohmmeter between the red/brown and the brown and it gives an open circuit with the key in any position. At this stage my brain has turned to jelly and run out of both ears, please help lol Andy