Hi All,

I've got the MoT coming up and need to resolve a problem that is baffling me. I hope someone can help give me a pointer or 2.

The rear sidelights (driver's side) are being reported on Maxidot as failed. The bulbs it claims are broken are the 2 that are seperate to the main cluster.

"Easy" i hear you think - "Change the bulb(s)".

--important bit--

I did this, and the problem remains, on closer inspection, the bulbs come on for a few seconds, then switch off with the maxidot error following.

--/important bit--

Has anyone got any ideas on how to diagnose this? I'm stumped, staring at the wiring, nothing seems damaged and i'm not sure where to point.

Ta,

MPM

Corroded connections in the bulb holder, or maybe a plug somewhere to the side lamps. The car uses a resistive test, it pulses the lights and expects to see a resistance within a programmed range to say that the bulb is OK.

I assume that you have the correct bulbs fitted ?

Paul

Thanks for the reply Paul.

The bulbs are correct, and i've checked for stuff like corroded connection in the holder and damage to the wiring in the immediate area.

The most frustrating thing is that randomly, it'll work for a day or 2 before deciding to 'fail' again. If i could predict this, i would be able to sneak it through the MoT and work out the problem at leisure...

I'm going to try some LED bulbs later and see if they respond the same.

Ta,

MPM

Leds will fail for sure as unless you fit balast resistors the car will see it as blown bulb as there isn't sufficient resistance.

That was the theory i was applying, to see if the reduced resistance of the bulb changed anything - a stab in the dark i know

I've had this before, gave all contacts a good clean and it solved it for me .....could be a similar issue... Not happened since!

I had one of those blow the other week and it didn,t even register it on my non maxidot display.I wouldn,t have known unless i visually checked it.

Something is strange here.

As far as I am aware the 2x W3W sidelight bulbs are not monitored by the 'bulb warning' system, or at least they aren't on my Octavia.

Unless if they both go off at the same time then this provides enough of a drop in resistence?

One possible explanation is water ingress behind the boot carpet / CD multichanger. Leaky rear washer pipes leak over the wiring have been known to cause some weird and wonderful electrical gremlins.

I think your right Silver.I,m sure just the bulbs in the main holder are monitored.I just removed both my small side bulbs that are seperate from the cluster and i didn,t get any bulb error warnings on the dash.

Spent all evening (in the rain eurgh) looking into this with a friend last night.

It's the (RHS) Single filament bulbs that are switching off, and they are definitely registering as 'failed' on Maxidot.

Now, there's no evidence of water ingress (on either side), all contacts seem ok, i admit i haven't cleaned them thoroughly but it all works fine....for about as long as is takes to walk to the rear of the car when just the single filament bulbs power off.

Interestingly enough, randomly half way through the evening, they started working fine. Then, after we'd packed up, a quick check and they 'failed' again.

Incidentally, the LED bulbs behaved in exactly the same way, came on for a second or two, then powered down.

Essentially, the circuits all appear fine, but the 'computer' must be deciding something is up and is powering them down.

The last thing we considered was the distribution box under the steering column where everything comes from. We theorised that switching the left and right light clusters around may give us a clue - if the problem switched sides then the problem must be somewhere at the rear - if not - then maybe something more expensive is going wrong... :S

When we gave up the lights were working fine....i have no idea what tonight is going to bring though.

I bloody hate intermittant problems.

MPM

*edit: After some research - distribution box = Central Electronics Unit

Eep.

Well, some investigation last night found that the rear washer hose had split in the rubber hose to the boot lid. Water down the loom behind the light cluster on the left.

Found this, dried it all up and all is working so far....

...now to work out how to patch the pipe together as i don't forsee it being an easy pipe to swap out.

MPM

...

...now to work out how to patch the pipe together as i don't forsee it being an easy pipe to swap out.

MPM

Easy - go to auto accessory shop where they have all those little bags of bits and pieces. You need a straight connector like these

http://www.componentforce.com/category/249/pipe-connectors

Strangely enough, I think last week I got through my MOT with one of the middle w3w bulbs out. The guy said the main ones working was fine when asked retrospectively. No dash warning either, so I'd guess they're not linked to the bulb out warning