TT halogen fogs to led affecting TT's left rear light?

[21wolfpupfq]

TV(2018 VW Atlas SEL 4motion) has LED running/headlights but with halogen fogs So in my infinite wisdom and with Mr Google, Youtube & Amazon's help, I've decided to replace the fogs with aftermarket leds(direct bulb replacement).
Everything worked seamlessly until I got a warning of bulb issue on the dash on way home from the weekend camping. At home, check of TVs light does not show any issues but TT's rear left light(1157) does not blink(turn,flasher or brightens when braking) but still turn on and filament seems to be intact. Right rear light is functioning as normal. Warning light on TV is gone when the TT's is disconnected. I guess I'll try to replace the bulb first and hopes that it resolves the problem. Thoughts?

[The Evil Twin]

Did you check the 1157 bulb? I believe that to be a dual filament bulb. The running light/ tail light is one filament and the brake/ turn is another. You could have one burned out and not the other.
I don't believe the fogs have anything to do with it. Then again, it is a VW..... (we have two and they often frustrate me. Lol) I used CANbus LEDs on my truck and the wifes VW to prevent erroneous light out messages from those bulbs.

[21wolfpupfq]

Yup, first thing was to pull the bulb - both filaments seems ok - not broken but with darkening at bottom.
If replacing the 1157 bulb does not rectify the issue I guess I can go back to the old halogen and see if problem disappears.
There's a post in motorhome forum about led light issue(main cause) that could be similar to my problem.

[Jim34RL]

It may be the vehicle electrical system. You need to research and see if the vehicle electric system is a CAN-BUS design. If so, the computer that controls the electrical load to your vehicle wiring may be looking for the resistance of the halogen bulbs that the LED lights do not have.

I know when I changed my lighting on my Ram truck to LED's I needed to purchase "drivers" that would trick the TIPM box that the proper lights were being used.

[21wolfpupfq]

actually the thread title is wrong it should be TV not TT - edited. The problem description is correct tho as I changed the TV's halogen fogs to leds , everything seems to work still except fot the TT's rear left light.
I do agree that is most likely due to the TV's electrical system/computer. I had an issue with my furrion rear observation camera not getting power when connected to a BT brake controller which was resolved by adding another furrion adapter to manage power being received/sent to the TT.

[Lins]

Does your TT have led lights? In the manual for our 2010 Tiguan, it essentially states that trailers with led's may cause a bulb out message. Your Atlas should be new enough that I wouldn't think that's still the case. We tow a 2 place snowmobile trailer with led's with our Tiguan and the only issue we see is the marker lights will flicker while the Tiguan checks for bulbs. If I leave the parking lights on while plugged in you don't see the flicker.

[21wolfpupfq]

No, TT has the old fashioned bulbs 1157. My good friend mechanic suggested(txt) focusing on the TT instead of the TV. I will replace the bulb first and go from there.

[Flybob]

The computer is looking for high current to the bulbs you replaced and not seeing any, it thinks they are burned out. I may require a certain load for the other lights to work as well. Not sure if you have a system reset, but sometimes resetting the system will recalibrate they system.

[Kcoulter]

Originally Posted by 21wolfpupfq

No, TT has the old fashioned bulbs 1157. My good friend mechanic suggested(txt) focusing on the TT instead of the TV. I will replace the bulb first and go from there.

Swap the TT left rear bulb with the right rear bulb....see if the problem follows the bulb.

[21wolfpupfq]

I guess I was over thinking the problem. < $5 dollar bulb(pair) replacement from WM did the trick. Left light is whole again.