Octavia III trailer lights not working after Rear LED retrofit

[jansajt]

Hello,

 

During last winter I retrofitted OEM rear LED lights onto my 2016 Octavia III Combi. I coded them with VCDS, no problem. 

Now I noticed that the lights on my Thule trailer hitch mount bike rack don't work anymore (the only ones which work are the turn signals).

I assume it's a problem with coding, since the bulbs and wiring on the Thule rack are ok and the hitch wiring too.

Does anyone have any ideas as to what the problem is?
 

The hitch is an aftermarket Westfalia A40V with a 7 pin socket, which was profesionally installed.

[varooom]

It will be you having made adjustments to the coding for your OEM rear lights, now your tow bar is no longer getting power supplied to the rear light on the socket.

 

Fixing it will be problem now, you may have to look very close at coding and try to get it working again, or take to professionals that did the tow bar and maybe they can code with your OEM LED lights.

[PetrolDave]

Have you tried changing the lights on the trailer that don't work to LEDs?

 

If the towbar fitment hasn't used the OEM trailer module then the lights could either simply be in parallel with the lights in the car, or energised by relays.

 

Since the car is now coded for LED lights any extra load (such as trailer bulbs) could appear as a 'short to ground', or the PWM signal used for LED bulbs could not properly energise a relay used to power the trailer lights.

I suspect the later since you don't mention the car lights not working .

 

Edited 10 September, 2022 by PetrolDave

[jansajt]

I measured the outputs on the trailer plug, and I'm getting no voltage on any lights but the blinkers. I assumed theres something with the led lights/ coding since the only lights that didn't need coding were the reverse and blinkers (since they use normal bulbs).

 

I also looked at the westfalia installation instructions (https://www.westfalia-automotive.com/fileadmin/pdf/e_anlagen/305/e305407391101.pdf), adn there si some connecting to the BCM module - so I think it isnt a simple parallel wiring.

 

My bike rack uses PR21 bulbs, which are gonna be hard to get, to try the led bulb thing + I wanna be able to use any normal trailer

[jansajt]

On 09/09/2022 at 17:06, varooom said:

It will be you having made adjustments to the coding for your OEM rear lights, now your tow bar is no longer getting power supplied to the rear light on the socket.

 

Fixing it will be problem now, you may have to look very close at coding and try to get it working again, or take to professionals that did the tow bar and maybe they can code with your OEM LED lights.

Do you think I'll be able to find any obvious options or that I'll have to take a look at some long coding?

[varooom]

It is knowing which module(s) that get adjusted during the coding of the car to tell it that it has towbar electrics, sadly I do not know what get's adjusted.

 

Unless you can locate a function that enables power to be sent to the towbar electrics in the coding with your OEM LED tail lights, then you are stuck.

You will have to remove or contact towbar manufacturer for support I suspect.

[PetrolDave]

12 hours ago, jansajt said:

I also looked at the westfalia installation instructions (https://www.westfalia-automotive.com/fileadmin/pdf/e_anlagen/305/e305407391101.pdf), adn there si some connecting to the BCM module - so I think it isnt a simple parallel wiring.

There's a long list of coding in an embedded link, with e.g. VCDS, I suspect that something there has been missed.

 

Changing the Leuchte coding in the BCM only affects the bulb concerned, as the Westfalia module I can see replicates the official Skoda trailer module all the functions are controlled using the CAN bus so I think it's reasonable to assume that changing the bulb coding on the car to LED is not the cause of your problem.