Fog light issue

[Richard75]

Skoda octavia vrs 2012

Car has just failed mot because the rear fog is only on, on the nsr.  Not drivers side.. I swapped sides with the bulbs.   So I know both bulbs work..  I have seen you can have both sides on. But no idea how to do this? 

Any help appreciated as I have limited time to sort this problem before mot expires... 🤯

[AGFalco]

If you only have one rear fog light bulb then it needs to be on the offside/drivers side.

 

If both bulbs work, is there voltage at the bulb holder with the fog lights turned on?

If no, then is there a fuse just for this bulb?

 

Thanks, AG Falco

[MikeTheThinker]

1 hour ago, Richard75 said:

limited time to sort this problem before mot expires..

If - as you state at the start of the post - your car has failed the MoT then any time remaining on the old certificate is lost.  If you use it on the road now before a successful test you are liable for a £100 fine and maybe some licence points.

 

[Richard75]

1 hour ago, AGFalco said:

If you only have one rear fog light bulb then it needs to be on the offside/drivers side.

 

If both bulbs work, is there voltage at the bulb holder with the fog lights turned on?

If no, then is there a fuse just for this bulb?

 

Thanks, AG Falco

The bulb holder works, connectors are identical apart from the clips. So I swapped sides and ut works fine, so problem has to be in connector or the wire in the loom itself. It does have left and right fuses, but for all lights on left or right..

[langers2k]

From factory, only the drivers side rear fog light should work.

 

It feels like someone may have messed about with the cars coding or something to get this behaviour...

- Any history or previous work done to the car?

- Have you had it long?

- Have you got any error lights/bulb out warnings etc?

[J.R.]

I will swop your problem with mine, I have to enable the LHS foglight of my RHD Yeti  for the French CT test quite soon!

 

Yours is a RHD vehicle isn't it?

[Richard75]

17 minutes ago, langers2k said:

From factory, only the drivers side rear fog light should work.

 

It feels like someone may have messed about with the cars coding or something to get this behaviour...

- Any history or previous work done to the car?

- Have you had it long?

- Have you got any error lights/bulb out warnings etc?

Had the car 18 months so passed last mot like it.  I was looking at the coding as a possible issue.  Could it be coded for europe.  I do get a warning saying I have a light out on that side but all others work so maybe its coded for dual? I dont wanna start playing with the electrics in case it is a coding issue. Is that a main dealer job? Or can any decent garage diagnostic kit sort this out?

[Richard75]

8 hours ago, J.R. said:

I will swop your problem with mine, I have to enable the LHS foglight of my RHD Yeti  for the French CT test quite soon!

 

Yours is a RHD vehicle isn't it?

Yes it is.

[langers2k]

Completely depends how good the dealer or independent is and what the problem is!

 

First thing to check is how the tail/fog lamps are connected. At least on my old 2012 hatch it had a P21/4W bulb with the 4W filament disconnected, it would always use the 21W filament but dim it using PWM for tail light use. You can easily check by:

- counting the wires to the tail lamp, 5 wires suggests your car does the same, 6 wires suggests a separate tail light feed

- looking at the working side, does it use the same filament for both tail and fog

 

This will hopefully help narrow it down between wiring and coding

 

Coding gets a bit more interesting, quick bit of background, the BCM (body control module) is responsible for the external lighting on this age of Octavia. As the same module can be fitted to various VAG cars, the lighting configuration is adjustable to support the different lighting options used, it's mostly controlled by byte 18 in the BCM coding.

 

The problem with the Octavia is that none of the byte 18 values match it's lighting so it's normally set to 00 which a 'custom' configuration applied using dealers tools such as ODIS.

 

This means that most independents won't have the tools or knowledge to correct issues in the light config. A dealer 'should' be able to reset the config using ODIS but again, training can be patchy so you'd need to find a dealer with at least some clue.

[Richard75]

8 hours ago, langers2k said:

Completely depends how good the dealer or independent is and what the problem is!

 

First thing to check is how the tail/fog lamps are connected. At least on my old 2012 hatch it had a P21/4W bulb with the 4W filament disconnected, it would always use the 21W filament but dim it using PWM for tail light use. You can easily check by:

- counting the wires to the tail lamp, 5 wires suggests your car does the same, 6 wires suggests a separate tail light feed

- looking at the working side, does it use the same filament for both tail and fog

 

This will hopefully help narrow it down between wiring and coding

 

Coding gets a bit more interesting, quick bit of background, the BCM (body control module) is responsible for the external lighting on this age of Octavia. As the same module can be fitted to various VAG cars, the lighting configuration is adjustable to support the different lighting options used, it's mostly controlled by byte 18 in the BCM coding.

 

The problem with the Octavia is that none of the byte 18 values match it's lighting so it's normally set to 00 which a 'custom' configuration applied using dealers tools such as ODIS.

 

This means that most independents won't have the tools or knowledge to correct issues in the light config. A dealer 'should' be able to reset the config using ODIS but again, training can be patchy so you'd need to find a dealer with at least some clue.

It has 5 wires. I put a multi meter on it tonight.  With sidelights on only there was a 2v feed going to bulb on both sides.  When I put fog lights on I had 12v on the good side and the same 2v on the side not working...   this seems to suggest the wiring loom is ok but the car is coded wrong for UK? Or am I missing something? I spoke to mot centre and they said aslong as it's working for the mot you can do what you want.  I'm thinking of running a wire from live wire on good side to the live wire on the badside?  Electrics on cars is not my strong point but should be all good if I use proper connectors etc? Skoda cant see car till jan 6th and mot runs out on 26th dec. So I gotta bodge it somehow and this seems bestway?

What do you think???

[langers2k]

Based on that, it does feel like the car coding has been messed with for some reason but the wiring is fine.

 

Depending where you are in Suffolk, if you fancy a trip to Norfolk I can take at the cars coding and lighting configuration for you.

 

If you want to fix this with wires, don't connect both sides together, instead, run a wire each way to swap them over. A better plan might be changing the two pins at the BCM, T52aa/6 and T52ac/47, not sure if there is enough slack to make that super easy or not.

[Richard75]

Whereabouts in norfolk are you I'm bury st ed....  yeah I can see how crossing the live wires over would be better..   thanks

 

[Morph]

I had problems when I turned on the passenger side rear fog via the OBD. 
It worked initially then stopped and it threw up an error. No matter what I did I couldn’t resolve it so just switched it off again. Now just drivers side works but no problems. 

[Richard75]

On 16/12/2021 at 20:24, langers2k said:

Based on that, it does feel like the car coding has been messed with for some reason but the wiring is fine.

 

Depending where you are in Suffolk, if you fancy a trip to Norfolk I can take at the cars coding and lighting configuration for you.

 

If you want to fix this with wires, don't connect both sides together, instead, run a wire each way to swap them over. A better plan might be changing the two pins at the BCM, T52aa/6 and T52ac/47, not sure if there is enough slack to make that super easy or not.

Crossed the wires today. All sorted now.  Used bullet connectors so I can remove when I want.    Took about 45 mins from start to finish and less than 10 quid.   Back for retest monday.. 😁 thanks for answering anyway..  

[langers2k]

Nice, that should sort it for the mot! 

 

I'm out in Swaffham so if you want to take a closer look at the coding etc in the New Year, we can sort something out. Just drop me a PM 👍

[Richard75]

15 hours ago, langers2k said:

Nice, that should sort it for the mot! 

 

I'm out in Swaffham so if you want to take a closer look at the coding etc in the New Year, we can sort something out. Just drop me a PM 👍

Ok mate cheers