Central locking problem

[Sambe30]

My central locking doesn't work, I've done the method of cutting and re joining the red and black wire to eliminate the door loop but still no luck, what should I try?

[magpie]

unplug the c/l relay , turn ignition on and plug it back in....does it click once ?

[Sambe30]

Unplug the wires from the back of it? Or does it have like a block connecter to unplug?

[Brianmoooore]

If the central locking is still completely dead, after doing the "red/black wire mod." correctly, then it's likely that the thermal fuse inside the locking ECU has tripped.
This sits in one corner of the circuit board, and consists of a small leaf spring soldered to one end of a resistor. If the current to the ECU is excessive, or flows for too long, the resistor gets hot enough to melt the solder securing the spring, it springs away, and the circuit is broken.
The spring can be resoldered, but it is essential that you don't add any new solder to the joint. The original is a special low melting point solder, and any new solder added will raise the melting point, making the 'fuse' useless.
Note that the thermal fuse doesn't trip without a reason, so repairing it may not be the end of the job .

[BROOMY]

Check the fuse.

[Sambe30]

Checked fuse it's not that , and that seems a bit too much for me Brian

[Sambe30]

On the red and black wires I haven't soldered them together or used a block connector I have only twisted them together to see if it would work?

[Brianmoooore]

Checked fuse it's not that , and that seems a bit too much for me Brian

It won't be the fuse - that's only there for short circuit protection of the wiring loom. The overload protection is provided by the device I've described.
Get stuck in and open the ECU up. At least yopu can tell us if the spring has sprung!

[Sambe30]

Ok, where will I find that and how do I open it?

[Brianmoooore]

You'll find it deep inside the sill, underneath the 'speaker in the driver's footwell.
The cover is held on by the usual little plastic catches that you find holding these kind of things together. Just release them with a small flat blade screwdriver.

[Sambe30]

Will try tomorow before work, will let you know

[Brianmoooore]

Single screw for the 'speaker panel, three more screws for the 'speaker itself, lift out a plastic piece under the speaker that is held by a hook over the bottom of the 'speaker hole, two screws on the inner sill, directly below the 'speaker hole, then drag the ECU, complete with triangular mounting bracket out from its hiding place by the wires.

[Sambe30]

Right took it apart and the spring had sprung, re soldered it using the original solder, and Bingo worked first time, you said that may not be the end of the problem but seems to work fine does that mean I need to get a new unit?

[daimlerman]

Checked fuse it's not that , and that seems a bit too much for me Brian

Well done,you just needed a bit of confidence to tackle it!

It could,just,maybe,that the solder let go due to old age....but if the same problem pops up in a few days then you need to find out what is causing the overload.

[Sambe30]

If it happens again what is it likely to be?

[Brianmoooore]

Could be something as simple as a sticking lock motor, or as Malcom suggests, the solder could 'just have let go'. This is more likely top be as a result of previous slight overloads nearly melting the solder and making it brittle, rather than just old age.
If there is no sign of water getting into it (blocked sill drains?), then it won't be the ECU that is the problem.

[daimlerman]

Difficult to be sure,but poor earth somewhere,or a poor live connection,solinoid sticking,that sort of thing.

TBO,it's happened to me just once in ten years of E30 playing,and re-soldering the link sorted mine.Almost certain that the one that I dealt with is still in use!

[Sambe30]

Could it have been the door loop that caused it? I've now done that but it is only block connected at the moment. I will use it for a couple of weeks and if it hasn't gone again will solder it and hear shrink it, thanks for all the help guys

[Sambe30]

Some pics for you

[Brianmoooore]

No sign of water ingress across the bottom of the board, so that's good.
Use something like a wooden cocktail stick to hold the spring against the top of the resistor, and just melt the existing solder with a soldering iron. It will be as good as new.
Doubt if the red/black wire was responsible, but just put it back together and don't worry about it.

[magpie]

that was an enlightening read .

[Sambe30]

Exactly what I have done Brian, thanks guys!

[ianev]

does central locking operate (convertible) from both doors or just drivers?

[Brianmoooore]

Central locking should operate from both doors and the boot.