SOT : Car central locking repair.

My '04 Xsara Picasso has a fault with the central locking. For some time the remote hasn't worked, but that's no biggie, the car isn't used much.
Now, however, even using the key one rear door and the tailgate won't lock. Very limited info on the web tells me it's likely a broken wire in the driver's door flex, but I can't see one.
I can't find anyone to fix it, except for one place who'll charge £66 just to tell me if they can or not. I'm in Reading, any ideas?
Cheers
--
Clive

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On Tue, 21 Aug 2018 14:33:23 +0100, Clive Arthur

The chances are it won't be broken (in half) physically but broken inside the insulation.
One way of testing for that is either meter the voltages on the various circuits to see if they look right (difficult), get to both ends of the loom and check for continuity (equally difficult) or pull each wire as close as you can to where they flex and see if one feels 'elastically' and / or even breaks (still difficult)?
If one (or more) broken wires located you can either replace that section of loom (door bits to car somewhere) or replace the broken wires and hope the rest stay good. Often any bigger wires (earth or power) break first.
If you can get them all in plain sight (from where they go into the body and door, plus a bit) and give each wire a bend, you might see any broken ones (also difficult).
I guess it all depends on how much money you can afford to give to someone else in lieu of doing such initial experiments (given that it could be somewhere else, like a BCM)?
FWIW, I rebuilt the loom where it goes though the tailgate hinge on our 04 Meriva and it's been fine ever since. ;-)
It did require removing the tailgate lining and some of the rear post inner plastics (requiring some replacement clips as they all go brittle etc).
Cheers, T i m
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On 21/08/2018 15:39, T i m wrote:

That's interesting, and definitely counter-intuitive.
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wrote:

I think it's just down to a hardening of the insulation and then the ability of that insulation to be able to bend linearly. The thicker the wire / insulation the less ability for it to manage to bend without the insulation fracturing, closely followed by the conductors as then they work harden at the fracture point and fail themselves.
FWIW, I think there was a thinner wire that had also failed (that fed the stoplight feed to the LED one in the tailgate) and that then became earthed via the fractured earth cable (that was still providing an earth though the tailgate hinge and latch) and blowing the stoplight fuse.
As a temporary fix I insulated the ends of the fractured wires, replace the fuse and was able to continue with the two std stoplights. The bidet wasn't affected. ;-)
When I repaired the loom I replaced the couple of 'bigger' wires (earth and feed to the rear screen heater) with several smaller ones, allowing the bundle to retain better flexibility for longer.
Cheers, T i m
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On Tue, 21 Aug 2018 22:30:31 +0100, T i m wrote:

Many years, when hybrid mechanical-electronic ignition systems became common, one variant used a hall effect sensor in place of points. The cams on the distributor shaft driving a pulse which was amplified and created HT via the coil.
The pickup unit floated so the advance-retard could work. Over time, the insulation became baked, and the copper wire inside broke. Leading to a really annoying intermittent fault where the car would cut out idling at times, but restart and carry on (for weeks, sometimes).
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On Wed, 22 Aug 2018 13:03:32 -0000 (UTC), Jethro_uk

Aren't they the most fun (not). ;-(
And of course, you might stumble on that if you went though everything carefully, or you might not ...
Like the motorbike I was helping sort for daughters friend. The bike shop looked at it, did some stuff and then suggested the carbs were worn (float jet seats were non replaceable) and that we should locate a second hand pair (£600 *each* new).
If we had ... and if they had come with manifold rubbers and we had used them ... and the fault cleared, we may have concluded that it was indeed the carbs?
But every test I did on the carbs suggested there was nothing wrong with them ... and a spray of Easy-Start around the manifold gasket highlighted the actual cause (an air leak). Two new rubbers (and clips) later, it was running fine again?
Now, had we got a pair of s/h carbs for 50 quid and it had fixed the problem (because they happened to come with better rubbers), it would have been the same as we paid for new rubbers and clips, but at least I was happy these carbs were good (and jetted correctly for that bike) and the rubbers brand new, no idea if the second hand ones were going to be.
Cheers, T i m
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On Wed, 22 Aug 2018 16:07:15 +0100, T i m wrote:

Well I found it because a customer finally left the car with us "until it was fixed". We ran around in it for a few days and finally, one evening when we were bringing it in, it did it. Stalled, and wouldn't start. Within seconds I was there, and immediately diagnosed no spark.
After that it was just a case of dismantling the ignition system component by component. And in a rare example of God smiling, I started with the distributor :)
Of course, unlike electro-mechanical ignition, you never needed to touch the distributor - which was probably why the fault got "buried". But as soon as I started dismantling the distributor, the pickup wires parted, and it was obvious what the fault was.
After that, every service we removed and inspected the distributor. And found that at about 24,000 miles, it was a 1/2 chance of a broken pickup wire.
Apparently we changed so many, the the car manufacturer noticed their end. One spares outlet accounted for 80% of EU sales of that part ...
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On Wed, 22 Aug 2018 15:54:04 -0000 (UTC), Jethro_uk

It sometimes needs that sort of approach.

Wahoo!

Cool.

As you say, that was a (time saving) bit of luck.

Yup. We fitted a Luminition unit to the kitcar when we built it ~30 years ago and I can't remember the last time I touched any of it?

Isn't that a lovely feeling though. ;-)

Oh.

Wow.
And right across the EU eh, let's hope we don't lose access to that sort of database in the near future ... ;-(
Cheers, T i m
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On 22/08/2018 17:08, T i m wrote:

Don't be worrying about the data base. You will not be able to get spares for any car built in what is left of EU. No trade deal- no spares!
--
mailto : news admac myzen co uk

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On 23/08/18 03:32, alan_m wrote:

Stupid silly little boy
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He was being sarcastic.
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On 23/08/18 08:42, John Angus wrote:

No, he wasn't. Its T i m.
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No it wasn’t.
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Clive Arthur wrote:

Broken wire is a common problem on a Nissan Micra tailgate. Check that the tiny micro switch in the key fob has not fallen off. Also check that the battery in the key fob is okay. If you can't check, get some new ones from a Pound shop. They are okay.
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But that will not help with the failure to command locked some of the locks, will it? Most of the time these problems are bad connections or fractured wires in ribbon cables. Its going to be hard to find. It would be interesting though, to know if both non locking locks failed together, it might point the finger at a culprit more accurately though what connection one rear door and the tailgate may have to each other is hard to know. It could be they share a common return especially if its the driver side rear door. Brian
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Clive Arthur wrote:

I'd look for broken wires in on the doors etc which don't work.
Typically, there is a rubber 'tube' with three wires in the hinge area.
One is ground. One pulses to open. One pulses to close. If the ground one is broken, the door won't open or lock. If one of the others, the corresponding function fails.
You can generally replace the wire - replace the whole section (say 9") not just a tiny bit where the break is. If you do the latter, the join is a stress point and will fail, you want the new joints to be on a section that doesn't flex.
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Only time I've seen a three wire system was on a very old car. The common one (I've seen) is two wire, where the polarity reverses the motor. So a broken wire would stop it working entirely.
--
*My wife has a slight impediment in her speech. She stops to breathe.

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wrote:

Yeah, that’s how my Hyundai Getz does it, 2 wires reversed.
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Assuming an electric system, most these days are two wire. Feeding a motor which operates the locks. Reversing the connections to the motor makes it reverse so lock or unlock. (a motor and rack and pinion to move the mechanical lock is more efficient than a solenoid)
There is usually a controller of some sort. What this does is send out a timed pulse to the motors. So they operate then stop. Switches inside the key lock (often both front doors and perhaps boot) tell the controller to send a lock or unlock pulse.
Point being if one door locks, but doesn't unlock, unlikely to be a wiring fault as both wires are needed for it to do anything. And all the motors are usually parallel wired.
Modern cars might have the controller as part of other electronics.
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On 21/08/2018 14:33, Clive Arthur wrote:

On my VW Passat one of the rear doors would not open. The door lock has an electric motor which had got stuck. Revving the car up to get max volts then hitting the car by the lock whilst someone else kept pressing open and close eventually freed the lock.
hitting the
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