Hi

My Skoda octavia Greenline 2016 failed its MOT today as rear fog light not working. The garage said they can't fix as they don't have a auto electrician.

I am not getting any warning messages.

If I put the fog lights on the front ones come on a show the green symbol on the dash, when I try the rear no light come on and no symbol on the dash, I think that is normal yellow / amber symbol.

I have vcds and no error messages showing for this problem, only one showing are for the radiator flaps stuck open.

I changed the car battery few weeks ago.

I don't know how long it has been working as they are rarely used.

Could it be the switch? or anyone had this problem or have any ideas

Could be the bulb (always my first choice!), wiring, fuse, switch, and of course nowadays possibly even a tick not in a box in the software!

I'm still looking at the bulb first.. dunno if it gets flagged up for you in a 2016.

I doubt it’s the bulb, as you would still get the telltale light on the dash.

I would start with the fuse.

No-one has checked the bulb yet?

Definitely the starting point that makes most sense to me.

Looks to be powered directly off BCM, so there may not be any obvious dedicated fuse, nor direct, hard-wired link to telltale.

Looking (more carefully) at wiring diagram, it seems like it might be a single-filament bulb that does both tail light and fog light functions, presumably at different PWM drive levels. So that makes me think it may be on the input (switch) side that the problem is, assuming that it is working normally as a tail light.

EDIT:

(And after even more scrutiny...)

Brake light also appears to do the same, so there should be two distinct sources of tail light illumination, if I'm reading it right.

Pin 4 of right rear cluster connector (white/blue wire) goes to brake/tail bulb, pin 2 (blue/white wire, confusingly) is the tail/fog bulb.

So we may be back to a failed bulb filament, with it passing tail light test because brake light one is intact.

Edited 10 May10 May by Breezy_Pete

My 2015 Elegance has a separate bulb for rear fog, H21W which I'd never seen before.

Are you certain it doesn't come on at reduced intensity as a second tail light?

I was intrigued, so just had a look. Bear in mind this is 2015 Elegance so might be different to your 2016 Greenline.

As @Breezy_Pete said, the fog H21W comes on but dimmer as a sidelight, as does the brake P21W.. FOUR rear sidelights!

P21W goes to full brightness when brake pedal pressed, and H21W goes to full brightness when fog switched on. The 5W sides stay on.

I then took the H21W out to simulate a blown bulb, then very briefly got a message on the MFD to "Check rear right fog light". That message disappeared after a few seconds, but a little yellow triangle remained on the dash, and in the Car bit of the screen the warning remained , although I had to go looking for it.

Edit: Top.. yellow triangle on dash

Mid: fog and sides

Bottom: sides only

Those three pics filled the 10MB upload limit, was going to put up a pic of the screen for completeness, but we know what that looks like!

Edited 10 May10 May by hubrad

I tried swapping the bulb from the passenger side and still nothing.

I plugged in my vcds and tested the rear fog light and it came on and the symbol came on the dash. So it is the bulb.

Could the rear fog have been disabled some how and if so does anyone know how to turn it back on with vcds, only had it a few weeks and only used it to check for faults and for change car battery.

Other guess is it could be the switch

From what I understand so far re VCDS, it's working the computer switching, so sounds like your bulb and wiring are ok. Onto the switch, then.. amazing how a little bit of muck can interfere with such things.

It seems unlikely to me that the rear fog would have been disabled, unless someone was messing with VCDS and saved the wrong setting - I was looking for information and there certainly is a setting for both/left/right/none. I'll need my laptop history to check, but it was either on here or Ross tech forum. If you already have it (just ordered mine by way of a very late birthday present) you'll be able to check.

Yes I have one, do you know what it comes under? Can't see anything wrong with the switch, I ordered one which has arrived but received the wrong one.

Hi again, back on the right laptop now, so here goes.. it was on here all along!

Go to this overall thread: https://www.briskoda.net/forums/topic/299424-octavia-iii-vcds-adaptations-tried-and-tested/#comment-3567267

Then in the first post, which has the menu of adaptations, click on Enabling both rear fog lights

and follow what's said there.

i read something recently which referred to UK service personnel needing to change the foglight side for the continental roads, so I wonder if perhaps some previous owner of yours either disabled them completely or did it wrongly.

hi thanks I had already tried that and it didn't work but I was looking through different things on the vcds and found that the rear fog light was turned off.

So turned it back on took it back to the garage and has now passed its MOT.

Another problem as I was setting off to the garage was that the engine coolant light came on, checked and was fine. plugged vcds back in and wouldn't clear, so I disabled the sensor. This will be my next problem to look into. I do have a coolant problem as I have to refill it about once a month. This has happened since the water pump was replaced, so presume a leak