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Thread: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles

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  1. Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    It’s been said before, but it’s worth repeating. Don’t leave the car with the key in it if you have these symptoms:
    Car locks itself when it shouldn’t
    Lights-on warning buzzer stops working
    Dashboard door-open display stops working
    If fitted, the door-edge warning light and door courtesy light (puddle light) stop working.

    These are all symptoms of a failure of the door-open signal, which may be due to a problem with the door lock microswitch. Whatever the cause, you risk being locked out of the car - which is especially embarrassing when the engine is running, as I discovered the hard way.

    My experience of the problem On my car, a 3dr A3 8P, the problem turned out to be that furry plastic was interfering with the action of the microswitch. It proved perfectly possible to do a repair, contrary to the received wisdom that you have to replace the complete lock. For the gist of the repair, skip to the sketch later in this thread, or for the whole tedious story, read on.

    The diagnosis Owners will be well aware of the priceless feature that if you unlock the vehicle but do not open a door, it will re-lock itself after a time delay - a frequent source of frustration and unkind thoughts about the idiot who thought this was a good idea. That’s when it’s working properly.

    But if it does not receive the signal that a door has been opened, the system will re-lock itself after the given time, come what may.

    On my car, the problem was intermittent. If any door other than the driver’s door was opened, the system worked OK. Only the driver’s door sometimes failed to send the correct door-open signal. It’s not surprising that the driver’s door should tend to give problems first, since it is used the most.

    My vehicle has the red warning light on each door edge, which comes on when the door is opened. It was apparent that the light failed to come on whenever the door-open signal failed. This was a really useful trouble-shooting aid - much easier to watch the light than wait for the doors to re-lock.


    Many vehicles have just a reflector on the door edge, so don’t assume there’s something wrong if it doesn’t light up, as I did with my newly acquired A4 recently! If you only have reflectors, you will have to use the lights-on warning buzzer or the dashboard door-open display to monitor what’s going on. Note that the interior overhead light is not a useful monitor, because it’s not dependent only on the door-open signal.

    Anyway, with the door open, I could open and close the lock by manipulating the latch plate. When closing the latch the light would always go off correctly.

    Latch closed, light off.

    When opening the lock, (by lifting the exterior handle), the light sometimes failed to come on, and this failure seemed to be linked to a reluctance of the latch plate to spring to the fully open position. When I encouraged it into position manually, I could just hear the click of a microswitch. (You need good hearing and really quiet surroundings for this. A stethoscope might help, but then you run out of hands to hold everything........) When the switch clicked, the light always came on. This suggested that the switch itself was OK, and the problem was friction in the mechanism.

    If the problem is not intermittent If the door-open signal refuses to trigger, there is less scope for diagnosis with the lock in situ, but it may still be worth exploring.

    If when you open the lock the latch plate springs fully open, you will need to restrain it manually and allow it to open slowly while listening for the microswitch. You can then repeatedly operate the microswitch by jiggling the latch plate. If the light can be persuaded to come on sometimes, this would suggest an intermittent contact within the microswitch. If it refuses to come on at all, this might also suggest a poor connection or a broken wire outside of the microswitch.

    If you don’t hear the click at all, this could imply the microswitch button is worn down, or the switch mechanism is broken, or background noise is obscuring the click, or perhaps you are deafer than you thought.

    Audi diagnostics / VCDS There is always the possibility that the failure of the door-open signal is due to an electronic failure either within the lock or in the central-locking control unit. I have no knowledge of VCDS, but I assume it should be able to tell if this is the case. Perhaps someone can confirm? But I would always look for a mechanical failure first.

    The solution On my vehicle as I say, friction in the mechanism appeared to be the problem. Application of WD-40 to the latch plate did not help.

    The microswitch is not available separately, and Audi quoted nearly £100 for a new lock, or about £230 fitted. It must be said that the lock incorporates the central-locking solenoids and components, so it is quite a complex mechanism. No doubt it includes a number of buried microswitches, but the one we are interested in turns out to be easily accessible once the lock is removed.

    Plenty of incentive then to try a diy solution. First we must remove the lock.

    Removing the lock The procedure is in the Haynes Manual. It’s quite complex because of four connections to the lock which have to be removed, those to the lock cylinder and the exterior handle being particularly tricky to get at. For this reason, the procedure includes removal of the window glass and window frame, the lock cylinder and the exterior door handle, as well as all the door interior trim.

    I have to admit that I didn’t have the benefit of the Manual at the time, so I removed only the door interior trim and kept the window fully up throughout. This forced me to remove the lock connections entirely by feel in a very limited space, and re-attach them in the same way - almost impossible, and I wouldn’t recommend it unless you have loads of time and unlimited patience. The Haynes method involves a lot more disassembly, but is less risky to your sanity.

    I’ll not dwell further on the procedure, just include the odd photo.



    A method of levering off the black plastic inner panel which seemed to work.




    The easy bit, removing the lock fixing screws - 8mm XZN (12 spline) bit.



    The lock removed.

    The repair With the lock removed, the microswitch is found on its bottom edge, held in place by a spring clip, so is easy to detach. The connecting wires between lock and microswitch prevent you from moving it far, but that’s OK.

    It was immediately clear that the microswitch is operated by a cam on the latch plate. The latch plate is plastic-coated and the problem was that the plastic coating had shredded where the microswitch bears on it, so that furry bits of plastic were interfering with free action of the cam and microswitch.


    The solution was simply to cut away the plastic coating locally with a knife, so that the microswitch could bear directly on the metal cam.

    Removing the plastic left a gap between cam and microswitch, so I had to relocate the microswitch closer to the cam by a mm or so. There are two round plastic locating pips on the microswitch which had to be trimmed with the knife, as shown. I then added packing under the microswitch to hold it in its new position. Needed a bit of trial and error to get it right.

    Then it’s just a matter of putting everything back together.

    Conclusion Not the quickest or easiest of jobs, but satisfying , as it cost nothing. The lock has been operating successfully for over a year now.

    Design fault or one off? I have no idea how common this problem of shredding of the plastic coating might be. My A4 appears to have the same sort of plastic coated latch plate and I imagine a similar arrangement of latch plate/microswitch may be used on other VAG vehicles, and maybe across the industry generally. The problem appeared on my car at about 5 years/85,000 miles. If anyone out there has a comparable experience, I hope they will share it with the Forum by posting a reply.

    If the shredding problem happens a lot, it would seem like something of a design fault. Of course if the industry can charge for fitting a new lock each time, it won’t be in a hurry to do anything about it.

    Replacing the microswitch If the switch ever needs replacing, I would have hopes of finding a not-too-dissimilar replacement from component suppliers such as Maplin, though one might need to be inventive with the mounting. Again, if anyone has experience of doing this, I hope they will post a reply.

    Inability to disable the alarm sensors Another consequence of a door-open signal failure which should be mentioned is that the alarm disabling switches stop working. These are the two push-buttons which allow you to
    a. disable the interior monitor if you want to leave a pet in the car
    b. disable the vehicle movement sensor if you want to leave the car on a ferry or tow it away.
    You will not be able to disable the sensors using these buttons, but at least this should be apparent because the little light on each button will fail to light up. The only alternative I can think of is to leave the car unlocked - not very desirable, and an extra incentive to get the problem fixed before the need arises. Many thanks to Forum member Roosterman for highlighting this aspect of the problem.
    Last edited by djgilson; 04-07-2017 at 11:54 PM.
     
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  2. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
    #2
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    Excellent, detailed write up mate - thanks very much.
     
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  3. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    This looks likely to be the problem with my wifes A3 (2004 1.6 sport ). Sometimes while driving the door opening signal comes on in dashboard display, sometimes the alarm goes off after being parked for while. After checking I found that it was not always locking the drivers door, I found that the only way to check apart from trying the door is to watch if the indicators flash when you press the lock button on the remote. Looks like the micro switch is causing the problem ?
     
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  4. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    kpn wrote
    This looks likely to be the problem with my wifes A3 (2004 1.6 sport ). Sometimes while driving the door opening signal comes on in dashboard display, sometimes the alarm goes off after being parked for while. After checking I found that it was not always locking the drivers door, I found that the only way to check apart from trying the door is to watch if the indicators flash when you press the lock button on the remote. Looks like the micro switch is causing the problem ?
    I'm guessing really, but the symptoms you describe sound more like a problem with the door-closure microswitch rather than the door-open microswitch - yes, there are two separate switches for these functions, as far as I can make out.

    You may be able to get some idea of what’s going on by opening the door and then opening and closing the latch plate in the way I describe. As I recall, the click of the closure microswitch is even fainter than the click of the door-open microswitch.

    Unfortunately, I think the door-closure microswitch is buried within the lock and I’ve no idea whether it’s a reasonable diy job to get at it. This always assumes it is a microswitch problem at all. Sorry I can’t be more helpful.
     
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  5. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    Thanks for your advice, I think its getting beyond my capability. I will speak to my local body shop and get a quote for the lock replacement. Hopefully not to expensive.
     
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  6. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    This is identical to the problem I currently have on my A3 and resulted in me locking my keys inside the car after unlocking it, opening the driver side door and putting my keys on the driver seat before shutting the driver door and hearing the clunk of the door locking. D'oh!

    Anyway, my car was into the dealer for it's service so I asked them to take a look at it and they diagnosed the issue being with microswitch and quoted me £190 to replace it. It's more of an annoyance than anything else so I politely turned them down on that offer!

    Cheers for the advice on how to sort it through!
     
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  7. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    Quote Originally Posted by dunnie View Post
    This is identical to the problem I currently have on my A3 and resulted in me locking my keys inside the car after unlocking it, opening the driver side door and putting my keys on the driver seat before shutting the driver door and hearing the clunk of the door locking. D'oh!

    Anyway, my car was into the dealer for it's service so I asked them to take a look at it and they diagnosed the issue being with microswitch and quoted me £190 to replace it. It's more of an annoyance than anything else so I politely turned them down on that offer!

    Cheers for the advice on how to sort it through!
    I have done the daughters A3 a couple of weeks ago.
    Lock from Stafford Audi's ebay shop was £45 and an hour to fit..
    A4 2.5 tdi QS (mapped)


     
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  8. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    I'm currently living with this problem on my A3.

    I don't think I will ever forget my experience of finishing work at 12.30 on a Friday and then managing to lock the keys in my car because of this fault. Spent most of the afternoon waiting the car park for someone to bring me my spare key!

    Have had the door trim off but couldn't work out how to get to the lock so this guide is great. Might attempt it next weekend. Although with this many people getting the same problem Audi ought to do something to sort it out, it's like the glove box hinges all over again!
     
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  9. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    Quote Originally Posted by sarah_a3 View Post
    I'm currently living with this problem on my A3.

    I don't think I will ever forget my experience of finishing work at 12.30 on a Friday and then managing to lock the keys in my car because of this fault. Spent most of the afternoon waiting the car park for someone to bring me my spare key!

    Have had the door trim off but couldn't work out how to get to the lock so this guide is great. Might attempt it next weekend. Although with this many people getting the same problem Audi ought to do something to sort it out, it's like the glove box hinges all over again!
    Thanks for posting, sarah a3. Sorry to hear you have this problem.

    When you've determined the precise nature of your fault, and hopefully fixed it, I hope you'll post the details here, including vehicle age and mileage.

    I had hoped this thread would build up a database of members' experiences on this issue. Perhaps your case will get the ball rolling! I guess the problem is there aren't many of us prepared to have a go ourselves, so most people just have the lock replaced and never find out the exact nature of the fault.

    Anyway, good luck with your investigation.

    David Gilson
     
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  10. Re: Lock microswitch problem / Door-open signal failure / Car may lock you out / May affect other VAG vehicles 
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    Hi David and others,

    Well today I managed to get at the door lock on my car (It's a 2004 A3 2.0TDI Sport for reference - also in mauritius blue pearl - coincidence perhaps?!)
    I removed the lock very easily - I didn't bother following my Haynes manual's advice to remove the window. Basically stripped the door trim and just disconnected the little rod from the handle at the lock rather than at the top near the handle. Then it was just a case of removing the 2 XZNs and the lock mechanism came out. Having removed the microswitch I noticed it was very clogged up with grease - I've read elsewhere that Audi spray unhelpfully thick grease on the locks during services so perhaps there is some truth in that as there was certainly enough of the gunge to make me think that was the problem. Unfortunately it wasnt, I removed the microswitch's cover to find the most miniscule plastic lug holding a tiny spring had snapped, leaving the contact loose in the switch - there's my intermittent door problem then!. The switch is made by Saia-Burgess - googling this I found out its an even more common weakpoint than I thought. After a couple of house with some superglue and various possible plastic lug replacements I gave up, deciding that it would only ever be a temporary fix. The internals of this switch are absolutely tiny and so fiddly.

    So to ensure no more wake up calls from my car alarm in the middle of the night I adapted the switch to permanently show the door as closed for now while I look at getting one from a car breakers. Leicester Audi want £102 for the whole mechanism which is irritating as the microswitch really is a 10 pence type component for Audi. From the brief reading around Saia-Burgess, some people seem to have tried just replacing the microswitch with some sort of radioshack alternative and in some cases the same Saia-Burgess switch that doesnt have the Audi custom 'locating pips' on but I don't know that I can be bothered faffing around with this as a solution.

    So that's it for now, I'm back to just having to live with the risk of locking my keys in the car - but I'm well practiced at that having lived with this for almost a year! Looking at trying my luck with a second hand part for around £30.

    I would discourage anyone from paying Audi to fit a new lock - fair enough if you want to pay £100 for the new lock itself but it's a relatively easy half hour installation and that's coming from a woman! Would be happy to help anyone local with this task if needed.

    Sarah
     
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