Spent a happy afternoon disassembling the front passenger door on our 05-plate Fabia, after repeatedly observing the following behaviour.

If the car is unlocked with the fob, and just the front passenger door opened, it re-locks itself after a short while as if it doesn't know that door has been opened.  Not 100% of the time, but more and more often.

Also;  and noticed as long ago as a year back, is that sometimes when driving, the car either attempts to or actually does lock itself, partially or completely, and sometimes immediately unlocking again, often when braking or cornering. Locking and unlocking behaviours without any active input. All a bit random. 

I've made previous attempts to fix this second symptom, but all unsuccessful.  One involved repairing wires with cracked insulation in the drivers side a-pillar bellows, together with cleaning up and replacing some pins in the connectors at that pillar, as there was some corrosion evident, likely caused by water ingress past a poorly re-fitted rubber boot/bellows. Another was inspecting and 'contact cleaning' the same pins/connections on the passenger side. Yet another was an extremely optimistic (i.e. pointless) spraying of contact cleaner into the general area of the door-open microswitches, with no disassembly, just through the holes on the back edges of the doors.

 

For today's attempt, I was expecting at least the door open microswitch would need replacing, but wasn't really sure that that alone could explain both symptoms. Not done enough testing at all to be sure that what I found does cover both, but optimistic for now. Here's the lock, fully removed as per @Tech1e's guide for window regulator replacement; plus a bag containing a genuine replacement microswitch. 

 

I didn't fancy grafting that switch into the existing wiring, following a bad experience of having to revisit this work on my Polo after trying this shortcut. Two inline crimps are supplied with these microswitches to make such a technique easy. Soldering the wires directly to the pins of the connector on the topside of the circuit board was successful back then, on that one, at the second visit. Can't really remember why I didn't completely remove the old wiring from the board, possibly reluctance to do that final bit of disassembly to get at the reverse of the board, 'twas a few years ago, I forget. 

 

This is what the board looks like before complete removal. 

 

And this is the underside after removal, showing the connector connections and microswitch solder joints, all coated in a thick layer of brake-cleaner-resistant conformal coating of some type.

I couldn't really see much of the joints through this dark brown coating, but did think I was observing a little more movement than expected - when waggled gently - of the connector relative to the board.  Cleaned away by scalpel a few bits of the brown coating to get a better look, and one joint was particularly grim. It's the earth connection, which goes to the door open microswitch and some other places...

 

Here's a very brief video of it being waggled:

I swapped the new microswitch in as well, as it made no sense not to.

 

Everything's pretty much back up together again now, but only 3 out 10 rivets replaced, and no door card yet.  I will await feedback from the owner on both types of misbehaviour before finishing it off, I think.

 

 

 

 

 

 

Edited 10 September, 20205 yr by Wino

Interesting stuff. Looks like the repeated shock from the door slamming over the years might cause those solder joints to fail.

I'm having the symptoms you describe. Passenger door re-locks on its own after a few seconds while still open, and driver's door locks as soon as the door is closed, even while the car is running. Sometimes it locks and immediately unlocks while moving. Anti hijack works erratically. Opening the boot involves a bit of a dance too. I can't get the door panel off just yet because even suitable rivets are hard to come by where I live. 

juanse- it might pay to try applying a bit of solder and or flux to those joints( with a soldering iron, of course). In my experience soldered joints can fail, where the wires seem in perfect contact with the solder, but a bit of heat + flux remakes the joint.

30 minutes ago, VWD said:

juanse- it might pay to try applying a bit of solder and or flux to those joints( with a soldering iron, of course). In my experience soldered joints can fail, where the wires seem in perfect contact with the solder, but a bit of heat + flux remakes the joint.

Will have to spend some time on that, yes. Locksmiths around here only deal with the mechanical side of things and don't seem to like the electronic stuff involved. I haven't been too keen on fixing it for fear of making things worse.

I'll have a count-up of my rivet supplies this evening, if I have plenty left over after finishing this door, we could maybe come to some deal with mailing some out?

I fixed the fuel gauge on a workmate's Fabia at lunchtime by reflowing the joints on the infamous green connector of the cluster.  Couldn't see anything wrong with the naked eye even assisted by reading glasses; but under the microscope I could see 8 or 10 joints that had cracked and showed movement when waggled.

17 minutes ago, Wino said:

I'll have a count-up of my rivet supplies this evening, if I have plenty left over after finishing this door, we could maybe come to some deal with mailing some out?

That'd be lovely, thank you. 

2 hours ago, juanse_2691 said:

Will have to spend some time on that, yes. Locksmiths around here only deal with the mechanical side of things and don't seem to like the electronic stuff involved. I haven't been too keen on fixing it for fear of making things worse.

 

Don't be intimidated by a reflow job. Its straight forward if you do not make the simple mistake of not using (enough) flux.

There is no such thing as 'too much flux'

 

Step 1: Clean the tip of the soldering iron with some abrasive cloth or steel wool while tip is hot.

Step 2: Put some tin on the tip.

Step 3: Put a generous amount of flux on the joint that requires re-flowing

Step 4: Heat the joint until liquid/molten and remove the soldering iron.

Step 5: Let cool down slowly and inspect if the joint looks shiny. If dull/hazy. Reflow again starting at step 2.

 

If step 5 is successful clean up the remaining flux with some isopropyl alcohol.

You can practice on any scrap hardware till you feel confident you'll be able to reflow the actual piece you are trying to repair.

 

Soldering is the same thing except you add additional tin at step 4.

Apart from accidentally joining adjacent pins there's very little that you can do that would make matters worse; and that's easily reversed with a bit of solder wick.

Edited 18 December, 20205 yr by Wino

The rivet count says that I will only have 8 left after I finish this door, which isn't enough for another door. No idea how I ended up with that number, surely I would have bought them in multiples of 10? 

2 hours ago, Wino said:

The rivet count says that I will only have 8 left after I finish this door, which isn't enough for another door. No idea how I ended up with that number, surely I would have bought them in multiples of 10? 

haha don't worry then. It's gonna be a while 'til I decide on taking things apart. I'll have a look to see what I can get.