Punto central locking thinks a door is open

Hi
My Punto 2001 HLX has developed a central locking fault. Sometimes the 'door open' warning light illuminate when you're driving causing the interior
light to come on (most disturbing at night!), then it corrects itself. I've discovered it can happen if I brake hard.
What is worse is it's not possible to lock the car when the damn thing is in this mood. I took it to my local Fiat dealer and they've never heard of it. I booked it in for them to check it out but within 10 minutes the fault had gone away. The (helpful) engineer said the central locking could have it's own fuse so it's possible to deactivate it so I can at least lock the car manually. But it's so erratic it hasn't seemed worth doing yet.
Until I have a permanent fault which they can investigate I'm going to have to live with it. But if anyone can throw any light on it (not my interior light) I would be most grateful.
Thanks in advance for any help given.
Rick
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Not much fun is this sort of problem!
Try to locate which door is the culprit. The fact that hard braking causes the light to on suggest that chassis/door flexing is resulting in a door lock switch being activated.
Often a good spray of WD40 or similar light oil into the door lock catch mechanism followed by ten open and closes will free up any sticking. If this does not sort the problem that you will have to remove the offending door panel and lubriacate and check all mechnical linkages.
If the problem still persists the broken/damaged wires in the offending door jam area (where they continually flex as doors are opened and closed) is the next possible cause. If it is the drivers door that causes the problem then this normally being the most frequently used door then it will have the hightest likelyhood of damaged wires.
Nick /////

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Cheers Nick
I've assumed it's the driver's door but can't prove it yet and have given the mechanism a squirt of WD40 hoping it's reaching the right bits. I'll give it another go and do all the others before pulling off door panels. The boot may be a possibility so I'll give that squirt too.
Damage driver door wires is one I'll investigate but I've noticed all the cables are encased in a sheath and didn't want to open it up for fear of damaging others.
Thanks
Rick

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If you have to get as far as removing a door panel to access the lock mechanism/solenoid and can find no fault then this is the ideal time to take a look at the wires. Bit of a fiddle to do but does not require you to cut and sheeths. One just has to get slack at both ends (inside car & door frame by disconnecting connectors and then slide the loom through the sheeth/rubber boot. I don't have our Punto anymore so can't remember how it all hangs together and if there is an easy access connector inside the car by the A-Post, but I'm sure you will be able to work it out.
Nick /////
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Baldrick wrote:

This may be of some use and may be worth checking. I had an identical problem on a Tipo and proved very difficult to locate. On this particular model, the switch that tells the CL module the door is closed is located in the actual lock mechanism. So if you look at the electrical connection to the lock, some terminals active the motor and the others are connected to a small internal switch. The only way to find this out was to drill out the rivots that held the assembly together - so only done if you have a replacement.
I am not sure how the punto does things but I would be inclined to look at the actual switch rather than the wiring. On some BMW models, the switch is located in the door stricker pillar on the B pillar and not in the door itself - again I have known these to fail in such a way that the module thinks the door is open, often setting the alarm off.
Something to check.
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If it's any help you can solder a piece of fig 8 twin flex to two pins and push them straight through the wires to meter for voltage or continuity. Use fine nose pliers for the push. The two small holes in the insulation leave little risk of shorting after the pins are pulled out, but you could always add a turn of tape. Haynes mamual or similar should show if switch is part of a mechanism, or a separate item. Door switches in enclosed door panels and pillars, tend to suffer from condensation, damp, and corrosion due to lack of air circulation/movement. As a temporary measure you can always fake the door as shut by shorting the appropriate wires with a couple of wires soldered to a fuse, just in case you hit the wrong wire. You can also use a 12V bulb on a flex extension for convenient voltage testing, light going off/on is easier to see than most meters.
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Closure on this one...
The car eventually developed a permanent fault and the Fiat dealer located a faulty front passenger door lock mechanism.
Cost over 100
Thanks to those who offered assistance.
Rick

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