Central Locking Actuator

[TheMonzta]

The central locking on the N/S/R door of my Touring stopped working recently. I bought a replacement actuator and fitted it but still no joy.

If I put my test lamp on the connector whilst it is disconnected from the actuator the black wire is live for about a second when the doors are locked then goes out and the blue and grey wires remain dead.

When the connector is plugged into the actuator and the doors locked all three wires light up for a moment before going out.

Any ideas what the problem is and where I go from here?

[Brianmoooore]

The blue and the white wire should both be firmly clamped to earth, except for when the locking pulse occurs, when a 12 volt locking pulse should appear on the blue wire.
The black wire connects to the deadlock motor, and is effectively open circuit when the locking pulse occurs. The other side of the deadlock motor connects to the blue, so the 12 volt pulse will appear here too, via the motor winding.

[TheMonzta]

Thanks for the reply Brian. I'm no auto electrician that's for sure so are you able to point me in the direction of what the problem could be regarding my actuator? Is it likely that I've bought a second duff one or is the problem somewhere else in the loom?

[Brianmoooore]

Connect a piece of wire to a good earth, and tee it temporarily into the white wire. Try to lock the doors with this wire in place, but make sure you disconnect it before unlocking. Probably not a bad idea to include a 20A fuse in this wire.
Also, make sure the driver's door is shut, as the locking ECU will immediately unlock the doors again if you lock them with the driver's door open.

[TheMonzta]

Cheers for that advice Brian. I'll give it a crack first chance I get and report back.

[TheMonzta]

Connect a piece of wire to a good earth, and tee it temporarily into the white wire. Try to lock the doors with this wire in place, but make sure you disconnect it before unlocking. Probably not a bad idea to include a 20A fuse in this wire.
Also, make sure the driver's door is shut, as the locking ECU will immediately unlock the doors again if you lock them with the driver's door open.

OK Brian, I finally got a chance to knock off work early and have a go at your advice.

I did as you requested but still no action form the actuator. Neither the white, blue or black wires register on my test lamp when the locks are activated with the temporary wire tee'd into the white wire. Remove the 20A fuse from the temp wire and all three light again as before.

Any ideas?

BTW, as a test just to rule it out I swapped the working actuator from the opposite door to double-check and that didn't work on the problem door either. So it's definitely a wiring issue rather than a faulty actuator.

[Brianmoooore]

Any ideas?

TBH, not really! The white blue and black wires on one door connect to the same coloured wires on the other side by soldered joints in the loom, and the plugs and sockets in the B pillar.
I suppose you could use a meter to check for continuity between the matching colours o the two sides of the car. You will need to measure carefully for close to zero ohms, as there will be a low resistance between the wires via the windings of the lock motors still connected. May help to unplug the locking ECU.
Next step after that is to take the cover off the B pillar, and check out the plug and socket.
Did you try the "dud" locking motor in the other door?

[TheMonzta]

Any ideas?

TBH, not really! The white blue and black wires on one door connect to the same coloured wires on the other side by soldered joints in the loom, and the plugs and sockets in the B pillar.
I suppose you could use a meter to check for continuity between the matching colours o the two sides of the car. You will need to measure carefully for close to zero ohms, as there will be a low resistance between the wires via the windings of the lock motors still connected. May help to unplug the locking ECU.
Next step after that is to take the cover off the B pillar, and check out the plug and socket.

Hmmm, it's all getting rather complicated now. Not sure it's worth all the hassle really as the car's going to be sold soon. It's an annoying little fault I thought I was going to fix easily.

Did you try the "dud" locking motor in the other door?

Yes, I put the 'dud' in the other door and it worked fine.

[Brianmoooore]

Hmmm, it's all getting rather complicated now.

Can't be complicated, as the relevant part of the wiring is so simple.
It has to be something silly, like a badly crimped wire in the B pillar plug and socket, a broken wire where it goes into the door, or a badly soldered joint where the branch up the B pillar joins the loom at sill level.

[kawakiman]

I have exactly the same problem on the N/S/R door on my tourer, but if I lock the door then immediately unlock it and then re lock it the actuator works every time. Onlt affects the one door!