My light warning came on and I found the left rear lights misbehaving. There are three 21W bulbs in the board, the top one was working and the lower two were not. I replaced the two lower bulbs but the problem persisted. i tried swapping bulbs around, and I always end up with the top one working and the lower two not working. The seperate bayonet bulb is behaving normally, as is the indicator. Does anybody have a solution?

Ok, some other stuff to check/try.

 

What rate(s) do you get from the LH indicator and the hazard lights with al other lights off? And does this change with the sidelights and/or brake lights on?

 

Do you get any other "odd" behaviours, such as the tail light flashing opposite phase to the indicators? (one on when the other's off) or it lighting up when you put your foot on the brake?

My light warning came on and I found the left rear lights misbehaving. There are three 21W bulbs in the board, the top one was working and the lower two were not. I replaced the two lower bulbs but the problem persisted. i tried swapping bulbs around, and I always end up with the top one working and the lower two not working. The seperate bayonet bulb is behaving normally, as is the indicator. Does anybody have a solution?

 

There are four.

 

From the top:

 

1) 21W brake/tail

2) 21W indicator

3) 21W reverse

4) 21W fog/tail

 

In addition there are 2x W3W bulds seperate from the main bulb holder that create the 'C' shape tail/night light shape.

 

Which two bulbs aren't working?

 

Continuing this saga, having swapped some bulbs around reassembling and still having the light showing on the dash, the nex time the car was used, the dash light had gone out! Here we are 4 days later and there is no dash light and the lights all work normally. I changed nothing - just swapped some bulbs around. It suggests there is a dodgy connector somewhere, but where to look?

Sounds more like a dodgy bulb to me.

 

For the sake of £20 I'd replace them all.

 

As asked earlier which two bulbs weren't working?

Also the P21 bulbs are a 4w and not the 5w that are a lot more common, so make sure you have the right bulbs as that will cause a problem, took me a lot of head scratching before I realised.

Also just noticed Silvers pic has 3w as well.

There are four.

 

From the top:

 

1) 21W brake/tail

2) 21W indicator

3) 21W reverse

4) 21W fog/tail

 

In addition there are 2x W3W bulds seperate from the main bulb holder that create the 'C' shape tail/night light shape.

 

Which two bulbs aren't working?

 

 

I have a curve on this one.....

Just to clarify: I have a Scout (estate)

My top and bottom are single filament 21w's. What seems to happen is the CECM drives the top one at a lower current for sidelights and normal for braking. The lower one only seems to function as fog light, not a sidelight, (So no C shape) although that could be down to the upgraded CECM. Both sides are like this and I can't fit a 21/4 into the holders. No bulb warnings or errors either.

That is very unusual.

 

I too have a Scout, 2008.

 

My lower 21W bulb is single filament but dual function (fog/tail) and so I get the 'C' shape.

 

I've yet to see a MkII Octavia that does not have this configuration.

 

I don't know what the CECM does but why did you need to upgrade it?

CECM is the Central Electrics Control Module.

 

I replaced the original (23 bytes) to get cornering fogs back, and picked up footwell lights as well. However, it came from a Passat, although all the coding appears to be the same.

 

Interesting that yours is also single filament, as well though. Seems that it's not just the shape/fitting that differs between the hatch and the estate.

 

 

I will check through the coding tomorrow, just to be sure.

Yeah for some reason all estates use the single filament set up, and the hatch uses twin filament bulbs.

 

Never understood why.

Yeah for some reason all estates use the single filament set up, and the hatch uses twin filament bulbs.

 

Never understood why.

 

I like the idea, otherwise you waste half a bulb.

 

 

Sorted the non-c-shape on mine......

CECM Byte 10 controls "Rear Fog Light as Parking Light" %age.......mine was on 0. Set the % to 0D (13) to match the coding on the hatchback. Looks ok, although will check again in the dark.

I like the idea, otherwise you waste half a bulb.

 

That's the weird thing.

 

The hatch does use both filaments, the 21W/4W bulb uses the 21W filament for the brake / fog feature, and the 4W filament for the tail light feature.

 

On the estate the CANBUS or (CECM?) adjusts the power sent to the single filament bulb depending on which light output is required.

 

You'd think that they would use one way of doing it but on both body shapes?

That's the weird thing.

 

The hatch does use both filaments, the 21W/4W bulb uses the 21W filament for the brake / fog feature, and the 4W filament for the tail light feature.

 

On the estate the CANBUS or (CECM?) adjusts the power sent to the single filament bulb depending on which light output is required.

 

You'd think that they would use one way of doing it but on both body shapes?

 

It'll be CECM, CANBus, in theory, is the networking protocol used to connect everything together.

The coding between my hatch and estate now only differ where the footwell lighting and HIDs are configured...

 

Hatch:

E18A0F31101E140000110D000000008000197F075C50000C000000000000

Estate:

E58A0F31101E140000110D000000000080097F065C50000C000000000000

 

 

 

Yes, you'd think they'd be the same setup, especially as the controllers are the same too. Given that Skoda skimped on putting in about 8" of wire between the CECM and the light-switch (for auto-lights) you'd have thought they'd saved even more by not having 4 extra lines running to the rear clusters. Surely there's not *that* much difference between the hatch and the estate that you'd really need completely different looms?

 

I noticed the boot-lights are different too.

Sorry for the delay. As mentioned, the fault reappeared after 4 days, and I tookSsilverman 1011's advice and changed all the bulbs in the left assembly. Everything has worked perfectly since so- hopefully- the problem has gone. I checked the bulbs I took out with a meter and there was no obvious problem in that all the resistences of similar bulbs were about the same.

Fingers crossed I have a solution and the forum succeeds again!

Great result!