Intermittent bulb light fault

[screamingjack]

My wife’s car is a 2010 1.4 litre Polo.
For sometime, the bulb failure light comes on at irregular intervals. All bulbs appear to work apart from the boot light and I have tried a different bulb with no effect, it will not light up.
The problem appears to occur after opening the boot ( but not always).
I believe the boot light is controlled by the the boot closing mechanism, could the fault lie here and is the switch in the upper part or lower part and is it difficult to get at?
Any help would be appreciated.

[RUM4MO]

I'd be very surprised if the boot light is monitored by the "bulb fault" indicator!

From my experience of modernish VW Group cars, the spring contacts on some of the bulbs, if not all the small signal/position ones, are made from galvanised steel and not sprung plated brass etc alloys. So, with time, these "too rigid" cheap contacts physically displace the solder blob on the bulbs - and that causes an intermittent contact - you can check if this is happening by removing and checking all the signal/position bulb ends. If you can be creative with a soldering iron, just replace the bulbs, also some bulbs do age badly and so while still illuminating, have sections of their filament coils touching and then not touching, so the current flow could be changing and that could be annoying the bulb fail monitor in the same way that the "too rigid" contact after displacing solder on the bulbs will.

[amer6R]

I would.check if the plug for the headlights is seated all the way ( this happened to me )

[CarbonChaos]

As said I don’t think the interior luggage light is monitored by the bulb warning system,if as you say the fault occurs after opening and closing the tailgate then I suspect it’s one of the bulbs in the rear light clusters has a poor connection the act of opening and closing will have distributed the contact.
Remove both of the rear lamps and check or replace the bulbs

Also check your front position lamps as these are sometimes overlooked

[mirceaculita]

I had this problem. The rear parking light was not working all the time. It was because the coil inside the bulb was broken in such a way that after hitting a bump or giving the tail light the good old slap it would turn back on.

It took me some time to figure out why the light would come on because I would hit a bump while driving, break the parking light bulb and by the time I would get back home the bulb would be working again. I was lucky my dad caught it as I was reversing out of the garage.

[RUM4MO]

I remember once at work, with a light source we were using, the bulbs were too fragile, so until we could source more rugged versions, the plan was to get a "free to move" lamp fitting that had wires, connect it to a power supply and fit each of the previously "faulty" bulbs, and flick them with a thumb/finger to get them to re-weld the coil back together - that kept production test going for a few weeks until we had sourced better bulbs for that application.

[screamingjack]

Thank you for all your suggestions they have given me food for thought.

[screamingjack]

I think I have found the problem.
It appears to be an intermittent fault on the drivers side rear bulb light.
I took the cluster off and strangely all the catches that hold the two parts together were broken, although the Polo is now 11 years old and has done less than 50000 miles.
To my knowledge it has never been off before and i have had the car from new.
I will try a new bulb and see if that was the cause.
Thanks for your help.

[RUM4MO]

It must be about 4 years since I removed both rear clusters to make sure that I knew what bulb types were in them - and I seem to remember thinking that the clips that retain the bulbs assembly to the cluster looked quite fragile!

[whogives]

Hi, I have exactly the same issue with my wives car. As follows start the car rear light passenger light (side light) the push in bulb on fine. Open the boot, then close boot on fine. IF I turn the engine off, then open the boot, close boot turn engine on the bulbs not working, if I bang the light it comes on.

So the only time the bulbs not on is if the cars off, you then open the boot lid then shut it. then start car. (Shopping is the perfect example) have to get out bang the light. I've replaced bulbs, replaced the bulb holder itself. Had OBD11 on to see if any codes (Nothing) !!!

[RUM4MO]

The trouble you might have is - "is it the 12V that is intermittent or is it the body earth to that bulb - or all the bulbs?" - maybe you have already made it clear and I've missed it, I have forgotten if there is a second rear "side" light bulb, it might help if you switch on that side's indicator when this happens and then check if the rear indicator is also not working and/or the reversing light.

[stanjacko]

Similar thing happened to me some time ago. Basically what can happen when the bulb fails - due to heat etc. the wire can get soldered back together, meaning the light can still work and also not work at the same time. Now this changes the resistance of the wire and you get the fault light even though all your light bulbs seem to be working.

Read this on some other VW forum when I had the bulb fault light come on for now apparent reason, could be helpful to someone.