Assistance Needed for Programming BCM for LED Fog Lights on VW Golf MK7 (2014 TDI to

[ak77]

I am seeking assistance with programming the BCM module on my 2014 VW Golf TDI to enable LED fog lights after retrofitting a 2015 VW Golf GTI front bumper. Despite extensive troubleshooting and multiple attempts to configure the BCM using VCDS, the LED fog lights remain non-functional. Below are the details of my setup, the steps I’ve tried, and the current state of the system:
Vehicle and BCM Information
Original Vehicle: 2014 VW Golf TDI
Donor Vehicle (Front Bumper): 2015 VW Golf GTI
BCM Part Number: 5Q0 937 084 AC
BCM Component: BCM MQBAB M H16 0124
Coding: 03101842C24102FB4BE4400000040308100000000000000000 0000000000
Dataset Number: 5G0063v____ 0001
What Works
The LED fog light modules were tested manually with a direct 12V power source and function correctly.
The wiring harness delivers a confirmed 12V at both fog light connectors when activated.
Steps Tried So Far
Wiring and Voltage Testing:
Verified that the wiring harness adapters are correctly connected:
Left Fog Light → Leuchte12NL LB45.
Right Fog Light → Leuchte13NL RB5.
Confirmed that both connectors supply ~12V when fog lights are activated.
Adaptation Changes in VCDS:
Updated "Lasttyp" (Load Type) for both fog light channels:
Tried settings:
6 - LED Lichtmodul (LED Light Module).
32 - allgemeine LED bis 12W (General LED up to 12W).
37 - allgemeine LED bis 12W.
40 - allgemeine LED.
Set "Dimmwert AB" (Dimming Value) to 127 for maximum brightness.
Disabled "Kaltüberwachung aktiv" (Cold Monitoring Active) where available.
Error Location Evaluation Adjustments:
Set "Fehlerort mittleres Byte DTC-DFCC" to 0 or "Not Active" for both fog light channels.
Long Coding Adjustments:
Modified Byte 18 in Long Coding Helper:
Set Byte 18 to 20 (binary: 00100000) to activate Bit 5 for LED-specific settings.
Output Tests via VCDS:
Ran output tests for both fog light channels in Module 09.
Fog lights did not activate during output tests.
Ground and Continuity Checks:
Verified ground connections at both fog light connectors.
Tested continuity between BCM and fog light connectors—no issues found.
BCM Compatibility Check:
Confirmed that BCM model 5Q0 937 084 AC should support LED lighting based on manufacturer specifications.
No firmware updates have been applied yet.
Current Status
The LED fog lights remain non-functional despite confirmed power supply and functional modules.
No fault codes appear in VCDS after clearing, but the lights still do not activate.
Questions for Assistance
Are there additional coding or adaptation changes required for this specific BCM (5Q0 937 084 AC) to enable LED fog lights?
Could this be a firmware limitation of the BCM? If so, is there a recommended firmware update or replacement model (e.g., 5Q0 937 084 DD)?

Are there any hidden parameters or advanced settings in VCDS that I may have overlooked?
Should I consider using ODIS or another diagnostic tool to reprogram the BCM?
Could this issue be related to dependencies between halogen headlights and LED fog lights?


Any insights or guidance would be greatly appreciated! Thank you in advance for your time and expertise.

[DV52]

ak77: Hi.

Color me confused!!! I am absolutely flabbergasted to read that a 084 series BCM (which is used on MQB platform cars in Australia, England and Europe) have an active Byte 18!!!

Yes, when polled by VCDS, these 084 modules report a massive 30 x Bytes on the long-code string - but they have only 18 x active Bytes (meaning that the last active Byte is Byte17)! That's why Byte 18 -> Byte 29 are ALWAYS a zero-string on 084 series BCMs

And also yes, Byte 18, Bit 5 is a software switch for the fog-light - but I don't believe that this is correct for a Golf mk7 (or any MQB platform car). The VW models that use BCMs that have the dreaded Byte 18 active are PQ35 platform cars - like the Golf mk5 and Golf mk6. The BCMs on these earlier model Golfs also have a long-code string with 30 x Bytes, but AFAIK, ALL the Bytes are active

I have no idea what happens when a Bit on Byte 18 is forced - I would have thought that nothing happens, but I'm not sure

OK - back to your problem (and my confusion). I may be mis-reading your words, but in saying "Confirmed that both connectors supply ~12V when fog lights are activated" - do you mean that when the center turret on the rotary light switch is pulled-out to the first position, ~12V appears at the fog-light connector - but the LEDs do not illuminate?

If so, then doesn't sheer logic dictate that the problem is down-stream of the connector - meaning either,

1. LED polarity is incorrect,
2. The LEDs do not like the form of PWM that the BCM outputs
3. The LEDs are cactus
4. The lamps have an earthing problem?

Again, if so - a supply source at the connectors when the fog-light switch is energized is conclusive proof that the coding is OK.

Don
PS: Perhaps post-up a URL link to the seller of these fog-lights

[ak77]

Hey mate,

Yes to the below: also I have individually tested each fog light at direct battery connection and both work. The part used is the original GTI mk7 1st generation bumper with fog lights. VW Fog LED lights 2015 model.

"Confirmed that both connectors supply ~12V when fog lights are activated" - do you mean that when the center turret on the rotary light switch is pulled-out to the first position, ~12V appears at the fog-light connector - but the LEDs do not illuminate?
"
My conclusion is also the power is On upon the switch-activated mode, but the BCM for some reason cuts it off?
The power travels to the lights and activates the error on the component (Infomedia warning and dash). I have since disabled error reporting to see if I could force any action by adjusting the dimming channels.

cheers

Al

[DV52]

Al: Hmm..........again very confused about your response! Maybe post-up a BCM admap (as an URL-link - don't dump the data directly in your post) so we can see how this puppy is programmed!!

Don

[ak77]

Hey Don, thanks for helping mate Below is the RB5 LED fog light coded:

Thursday,13,February,2025,01:03:29:41771
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64(VMWare)
VCDS Version 24.7.1.0
Data version: 20240919 DS356.3
Ross-Tech: Home


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UDS Adaptation Channel (16B): ENG116949-ENG116119-Leuchte13NL RB5-Lasttyp 13
Stored value 6 - LED Lichtmodul


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UDS Adaptation Channel (16B): ENG116949-ENG116119-Leuchte13NL RB5-Lasttyp 13
Stored value 6 - LED Lichtmodul


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UDS Adaptation Channel (16B): ENG116949-ENG116129-Leuchte13NL RB5-Dimming Direction CD 13
Stored value maximize


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UDS Adaptation Channel (16B): ENG116949-ENG116133-Leuchte13NL RB5-Dimming Direction EF 13
Stored value maximize


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UDS Adaptation Channel (16B): ENG116949-ENG116137-Leuchte13NL RB5-Dimming Direction GH 13
Stored value maximize


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UDS Adaptation Channel (16B): ENG116949-ENG116124-Leuchte13NL RB5-Dimmwert AB 13
Stored value 127


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UDS Adaptation Channel (16B): ENG116949-ENG116128-Leuchte13NL RB5-Dimmwert CD 13
Stored value 0


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UDS Adaptation Channel (16B): ENG116949-ENG116132-Leuchte13NL RB5-Dimmwert EF 13
Stored value 0


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UDS Adaptation Channel (16B): ENG116949-ENG116136-Leuchte13NL RB5-Dimmwert GH 13
Stored value 0


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UDS Adaptation Channel (16B): ENG116949-ENG116121-Leuchte13NL RB5-Fehlerort mittleres Byte DTC-DFCC 13
Stored value 00


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UDS Adaptation Channel (16B): ENG116949-ENG116563-Leuchte13NL RB5-Lampendefektbitposition 13
Stored value 42


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UDS Adaptation Channel (16B): ENG116949-ENG116119-Leuchte13NL RB5-Lasttyp 13
Stored value 6 - LED Lichtmodul


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UDS Adaptation Channel (16B): ENG116949-ENG116125-Leuchte13NL RB5-Lichtansteuerung HD AB 13
Stored value Always


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UDS Adaptation Channel (16B): ENG116949-ENG116122-Leuchte13NL RB5-Lichtfunktion A 13
Stored value Nebellicht rechts


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UDS Adaptation Channel (16B): ENG116949-ENG116564-Leuchte13NL RB5-Lichtfunktion C 13
Stored value not active


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UDS Adaptation Channel (16B): ENG116949-ENG116127-Leuchte13NL RB5-Lichtfunktion D 13
Stored value not active


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UDS Adaptation Channel (16B): ENG116949-ENG116130-Leuchte13NL RB5-Lichtfunktion E 13
Stored value not active


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UDS Adaptation Channel (16B): ENG116949-ENG116131-Leuchte13NL RB5-Lichtfunktion F 13
Stored value not active


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UDS Adaptation Channel (16B): ENG116949-ENG116134-Leuchte13NL RB5-Lichtfunktion G 13
Stored value not active


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UDS Adaptation Channel (16B): ENG116949-ENG116135-Leuchte13NL RB5-Lichtfunktion H 13
Stored value not active

[DV52]

Al: First, let's get the basics correct.
I assume that you took my advice and reset BCM Byte 18 =00. If not, please do it because activating Byte 18 is not appropriate for this BCM! Also, re-reading your first post - I'm not sure about your words "Disabled "Kaltüberwachung aktiv" (Cold Monitoring Active) where available". I can find NO such channel on this BCM - so if made this change, please advise how this was done

OK, now lets deal with the more interesting considerations for this car!
As I suspect that you already know, Leuchte-programming for the fog-lights is very simple -so not much to get wrong (your settings are OK)

My understanding of your observations on this car is as follows:

1. You have confirmed in your previous reply that when the fog-light switch is activated, a 12V supply appears at the pin on the fog-light fitting connector (I assume with the LED lamps actually connected) - and the LEDs do NOT work.
2. You have also confirmed that the LEDs work when a direct battery voltage is applied to the lamps (I assume with the same physical set-up as in 1. above, but with the connector from the BCM unplugged to allow the battery volt connection).

The two findings above suggest (to me, at least) that there may be a compatibility issue between the Leuchte-set supply signal and the LEDs. I'm not sure if you are aware of the engineering protocol called Pulse Width Modulation (PWM) - this is the mechanism that the BCM uses to control lamp dimming. When you set the Dimmwert AB value to 127, the PWM part of the 12V signal should be very small- but there is still a PWM frequency in the voltage supply. Maybe the fog-light LEDs don't like this PWM frequency (this suggestion is a long-shot guess)?

My suggestion is that you experiment with the following:

1. Try running the LEDs as if they are incandescent lamps like this:
   • Lasttyp= 10 - allgemeine Scheinwerfer
   • Dimmwert AB = 100
   
   
2. Try different LED settings for the lasttyp channel. Yes, you have already tried some of these values - but experiment with different combinations of Dimmwert AB values:
   • 32 allgemeine LED bis 12W
   • 37 allgemeine LED bis 12W
   • 40 allgemeine LED
   • 43 allgemeine LED
   
   
3. Try different illumination levels for Dimmwert AB (IMO there is no visual difference between a value of 100 and 127)

Don

[ak77]

[QUOTE=DV52;1351884]Al: First, let's get the basics correct.
I assume that you took my advice and reset BCM Byte 18 =00. If not, please do it because activating Byte 18 is not appropriate for this BCM! Also, re-reading your first post - I'm not sure about your words "Disabled "Kaltüberwachung aktiv" (Cold Monitoring Active) where available". I can find NO such channel on this BCM - so if made this change, please advise how this was done

Ok, so I am isolating errors specific to LED errors. These two replace this from long coding to channel coding.

MQB Platform Differences:

MQB BCMs (e.g., your 5Q0 937 084 AC) handle cold diagnostics differently than older platforms like PQ35.

Some parameters are hidden or merged into other adaptation channels (e.g., Lampendefektbitposition, Fehlerort mittleres Byte).

Firmware/Software Version:

The visibility of "Kaltüberwachung aktiv" depends on the BCM’s firmware version. Newer BCMs (e.g., 5Q0 937 084 DD) may expose this parameter, while older versions do not.

So to disable :
---
Disable Error Reporting via Adaptations
Fehlerort mittleres Byte DTC-DFCC: Set to 00 (disables fault logging).
Lampendefektbitposition: Set to 00 (optional, disables defect tracking).


When I was reasoning with this in my head, I thought if triggered BCM halogen error wouldn't be stored it would allow parameter to activate the LEDs.

[ak77]

My understanding of your observations on this car is as follows:

1. You have confirmed in your previous reply that when the fog-light switch is activated, a 12V supply appears at the pin on the fog-light fitting connector (I assume with the LED lamps actually connected) - and the LEDs do NOT work.
2. You have also confirmed that the LEDs work when a direct battery voltage is applied to the lamps (I assume with the same physical set-up as in 1. above, but with the connector from the BCM unplugged to allow the battery volt connection).

Don

YES the above is as stated .

[ak77]

Thanks Don, I'm off to the garage to investigate, per your last suggestion. Brb

[ak77]

My suggestion is that you experiment with the following:

1. Try running the LEDs as if they are incandescent lamps like this:
   • Lasttyp= 10 - allgemeine Scheinwerfer
   • Dimmwert AB = 100
   
   
2. Try different LED settings for the lasttyp channel. Yes, you have already tried some of these values - but experiment with different combinations of Dimmwert AB values:
   • 32 allgemeine LED bis 12W
   • 37 allgemeine LED bis 12W
   • 40 allgemeine LED
   • 43 allgemeine LED
   
   
3. Try different illumination levels for Dimmwert AB (IMO there is no visual difference between a value of 100 and 127)

Don

Done all of the above now and no success:

Dimmwert AB: done at 50 , 80 , 100, 125, 150, 126 and 127.

[DV52]

Alek: Bummer!!!

Alas, I don't understand any of your words in your response above that starts "Ok, so I am isolating errors specific to LED errors. These two replace this from long coding to channel coding..........."

I reaching the end of my suggestions - I ask once more:

Maybe post-up a BCM admap (as a URL link - don't dump the data directly in your post) so we can see how this puppy is programmed!!

If you aren't familiar with the process of creating a BCM admap with VCDS, see my instructions below:

From the VCDS opening screen below, select Applications



From Applications screen, select Controller Channel Map



In the Maps dialogue box, set-up the variables EXACTLY as shown below (take care with this step - check the boxes correctly):



Press the Go button and wait for the magic to finish!

Once the process is complete, look in the sub directory C:\Ross-Tech\VCDS\Logs on your laptop and you should find a new file starting with the name admap-09-5Q0-937-084-AC.......CSV.

Now, because this forum won't accept a .CSV file, you will need to post-up the admap to a third-party hosting site (like dropbox, or any of the lots of other sites). Then include a URL-link to the file in a new post here

Don

[ak77]

Hi Don,

Here is the link where to download the file. Also included the text file format along the VCDs export CSV
Al
Unique Download Link | WeTransfer


1. Update Fog Light Adaptation Channels
Left Fog Light (Leuchte12NL LB45)
Current Settings:

Lasttyp 12: 6 - LED Lichtmodul ✅

Dimmwert AB 12: 127 ✅

Fehlerort mittleres Byte DTC-DFCC 12: 00 (Error reporting disabled).

Missing: Kaltüberwachung aktiv (Cold Monitoring Active).


Right Fog Light (Leuchte13NL RB5)
Current Settings:

Lasttyp 13: 6 - LED Lichtmodul ✅

Dimmwert AB 13: 127 ✅

Fehlerort mittleres Byte DTC-DFCC 13: 00 (Error reporting disabled).

Missing: Kaltüberwachung aktiv (Cold Monitoring Active).



Thanks mate

Al

[DV52]

Al: hmm.......... that's a mighty odd BCM admap!

Your BCM has P/N & S/N 5QO-937-084-AC. The nearest BCM in my database is an Aussie 5Q0-937-084-AE. I've created a BCM compare spreadsheet for the 2 x modules that you will find HERE

This is how the spreadsheet works:
Worksheet "BCM compare AC and AE"

1. Contains a list of ALL channels and values in your BCM compared to the AE BCM - if the AE BCM has the same channel name
2. The last column "Same?" asks the question if the settings are identical in the 2 x BCMs for each channel
3. I've sorted the results by the "Same?" column with "No" first (because these will be of greatest interest to you)
4. There are 2 x types of "No" results: If the 2 x modules genuinely have different values and if the AE BCM does NOT have the channel

Worksheet "AE channels not in AC"

1. Contains a list of channels that appear in the AE BCM - but the same channel is NOT in your AC BCM

As you will see - there are multiple (meaning many) "No Response From Subnet Component" values in your BCM! AFAIK, these BCMs don't have a Subnet!! MQB platform BCMs certainly don't use a Subnet mask because they don't have an IP based network - so the many, many instances of "no response......" in your admap is very strange!

What is the back-story for the BCM in this car? Shirley it can't be the factory installed module - or if it is, has there been some serious software tinkering?

Don

PS: The fog-light Leuchte-sets look OK

[ak77]

Al: hmm.......... that's a mighty odd BCM admap!

What is the back-story for the BCM in this car? Shirley it can't be the factory installed module - or if it is, has there been some serious software tinkering?

Don

PS: The fog-light Leuchte-sets look OK

Thank you Don, I appreciate the help thus far.

No history with the car that I know off. The wife drove for the last 3 years and had little front damage so I opted to upgrade the entire bumper and fog-lights from Gti . This is the TDI 110kw model R edition. So no issues previously.

[ak77]

I'm guessing you are implying this will have to be a firmware update, replacement, or resistors ?