Rear Fog Light stopped working Mk7 R Estate

[bainbad]

2016 Mk7 R Estate just failed MOT as Rear Fog not working. Rear Fog Bulb OK (tested) and fitted a new headlight switch from VW, correct part number (MOT mechanic thought the headlight switch was the culprit).
When headlamp switch in the Rear Fog on position (pulled out) there is no dash light for rear fog and no light on the headlamp switch.
Fault code found with Carista =
Central electronics
Part #: 5Q0937086AK
Component: BCM PQ37BOSCH
Software version: 0162
ASAM/ODX identifier: EV_BodyContrModul1UDSBosc
Coding: 03501A66C24122F30BA44080B11C07281000000000000000000000000000 (hex)
Fault codes:
267022 Manufacturer-specific code

Can find no information about that fault code. Emailed Carista but no joy.
As far as I understand it the BCM controls the power to the rear fog light and there is no separate fuse for the rear fog. Everything else is working fine and there are no other fault codes.

The car has only done 19000 miles and is in as delivered condition with no modification. Any advice would be much appreciated. I have looked a lot for solutions on the web. Saw a report of someone being charged £600+ by VW to get this fixed! Nearest VW dealer 35 miles away so if I have overlooked a simple way to fix this I would be grateful for any help.

 

[DV52]

hmm.......... I ain't ever seen a malfunction code 267022 (but then, I don't use Carista)!
Here's how the long code string on your BCM looks in a more readable form:

Byte Hex    Binary
00    03    00000011
01    50    01010000
02    1A    00011010
03    66    01100110
04    C2    11000010
05    41    01000001
06    22    00100010
07    F3    11110011
08    0B    00001011
09    A4    10100100
10    40    01000000
11    80    10000000
12    B1    10110001
13    1C    00011100
14    07    00000111
15    28    00101000
16    10    00010000
17    00    00000000

The software switches that tell the BCM how to operate the rotary light switch are on Byte 07. As currently programmed, your BCM thinks that the car has rear fog-lights fitted (because Bit 4 is set). Incidentally, the BCM thinks that this car doesn't have front-fog lights installed - is this true?

Based entirely on your words - I suspect this problem might be physical, rather than a coding issue.

Maybe as a first try - look at the state of the 10 x pin connector on the back of the rotary light switch. If the wiring loom and terminations look OK -here's how the light switch is wired:

As you can see, the fog-light wire is on pin #5. This ONE wire controls both the front and rear fog-lights. There is an electronic device inside the rotary light switch that sends a different signal to the BCM depending on whether the front, or rear fog-light position is selected. My initial hunch is that maybe this electronic-device has failed- perhaps?

Here's an oscilloscope trace of the various fog-light signals that are generated by the rotary light switch (and which should appear on pin #5 if the electronic device is healthy):

I'm guessing that you don't own an oscilloscope - maybe grab a multi-meter and set it to DC volts (try the 2 volt scale first). Place the black lead on pin#6 (earth) and the red lead on pin #5.

Check that the voltage on pin #5 drops when the rear fog-light position is selected. If you don't get higher volts on pin #5 in the fog-light OFF position, or if the volts don't drop with the center turret pulled-out, I would investigate if a new rotary light switch is needed?

Don

 

[bainbad]

hmm.......... I ain't ever seen a malfunction code 267022 (but then, I don't use Carista)!
Here's how the long code string on your BCM looks in a more readable form:

Byte Hex    Binary
00    03    00000011
01    50    01010000
02    1A    00011010
03    66    01100110
04    C2    11000010
05    41    01000001
06    22    00100010
07    F3    11110011
08    0B    00001011
09    A4    10100100
10    40    01000000
11    80    10000000
12    B1    10110001
13    1C    00011100
14    07    00000111
15    28    00101000
16    10    00010000
17    00    00000000

The software switches that tell the BCM how to operate the rotary light switch are on Byte 07. As currently programmed, your BCM thinks that the car has rear fog-lights fitted (because Bit 4 is set). Incidentally, the BCM thinks that this car doesn't have front-fog lights installed - is this true?

Based entirely on your words - I suspect this problem might be physical, rather than a coding issue.

Maybe as a first try - look at the state of the 10 x pin connector on the back of the rotary light switch. If the wiring loom and terminations look OK -here's how the light switch is wired:

As you can see, the fog-light wire is on pin #5. This ONE wire controls both the front and rear fog-lights. There is an electronic device inside the rotary light switch that sends a different signal to the BCM depending on whether the front, or rear fog-light position is selected. My initial hunch is that maybe this electronic-device has failed- perhaps?

Here's an oscilloscope trace of the various fog-light signals that are generated by the rotary light switch (and which should appear on pin #5 if the electronic device is healthy):

I'm guessing that you don't own an oscilloscope - maybe grab a multi-meter and set it to DC volts (try the 2 volt scale first). Place the black lead on pin#6 (earth) and the red lead on pin #5.

Check that the voltage on pin #5 drops when the rear fog-light position is selected. If you don't get higher volts on pin #5 in the fog-light OFF position, or if the volts don't drop with the center turret pulled-out, I would investigate if a new rotary light switch is needed?

Don

Hi Dan

Thank you for reply and for your time exploring the long code string that I posted for the BCM.

I did already try fitting a brand new rotary light switch from VW parts yesterday. The car only has the single rear right hand side fog light. There are no front fog lights.
The rotary switch part number is 5G0 941 431 BE (as on the label of the factory fitted old switch that I removed and verified for the new replacement switch by VW parts from the VIN number. This switch only has the single pull out position for rear fog lights.

You are correct, I don't own an oscilloscope. I do have a multimeter (AstroAI Digital Multimeter TRMS 6000 Counts Auto-Ranging Voltage Tester).

My Carista device does have a way of checking what type of bulbs are fitted. The only odd thing that I noticed is that Carista lists the rear fog light as a "Rear Left Fog Light" which is strange as the car is a right hand drive UK model so has a single Rear Right Fog Light. Is it possible that there is different coding for the rear fog light for RHD vs LHD models?

Three weeks ago the original battery gave out completely so I fitted a new Bosch AGM battery and used the Carista to register the new AGM battery. All seemed well, though I did not specifically check the rear fog light. I don't recall ever having used the rear fog lights but the car did pass the MOT the year before so presumably it was working then. I then took it to Awesome GTI, Irlam for a full service two days before the recent failed MOT and they ticked that all the external lights were working. Obviously they could have missed the non functioning rear fog light (they are not an MOT centre).

I would be able to do a wiring continuity check between the rear fog bulb holder and the plug for the fog light at the front of the car if I knew where that plug was. All the other rear light work. i assume that the wires to the rear light housing would all share the same conduit making it odd for just the rear fog light wiring to fail on its own?

I have re-run the diagnostic checks with the Carista and there are now three fault codes:
267022 Manufacturer-specific code (as per my original post) but also 919560 and 395521. Both of these are manufacturer-specific codes.
The Carista can clear these codes but the 267022 is the first one to come back.

I did wonder if I should try paying to use erwin to try to get information about these codes?

Tony

 

[DV52]

Tony

First, perhaps the following is useful regarding the physical part of your problem:
The wiring arrangement for the rear fog-light is like this for a RHD car:

Notice the descriptor T73a /72 on the BCM connector. This means pin #72 of Socket A (which has a total of 73 x pins).
For LHD cars, the wiring is exactly the same - but the yellow/white wire is terminated on the left-side inner tail-light fitting

A typical BCM looks like this:

The location of the BCM on a RHD is behind the glove-box (@ the lower left-side) like this:

Now for the coding part of your problem:
My apology if you know this stuff already - but on MQB platform cars like your mk7 (mk7.5?), each of the 35 x exterior lights is operated by what I call a "Leuchte-set". This is a bunch of 19 x adaptation channels within the BCM that start with the word "Leuchte". So, each lamp is controlled by a separate Leuchte-set and each Leuchte-set controls ONE pin on the BCM. The Leuchte-set for the rear fog light is Leuchte26NSL LA72.

I'm not familiar with a Carista - but I suspect that you could access the Leuchte-set above to see how the rear fog-light is coded (I'm happy to check the coding if you post-up the values). However, if no coding changes have been made - I'm not sure that this would be helpful

As for Carista calling this lamp the "left-side fog-light", this is not surprising. Notice LA72 in the Leuchte-set name above. The "L" means left car-side (incidentally, A72 means pin#72, Socket A on the BCM - this confirms the wiring diagram). Given that the fog light is positioned differently depending on the drive-side AND because the same pin # is used for both drive-sides, the labeling of this Leuchte-set as "Left" is nominal only (IMO, of course).

So - again I'm not familiar with Carista - but for diagnostic devices like VCDS and OBDeleven, the error descriptors for faults like a coding problem, or a lamp-out, or a broken wire/faulty-termination is specific to the type of problem. I'm not sure what Manufacturer-specific code means (I've not seen this descriptor on VCDS, or OBD11).

Don

 

[bainbad]

Hi Don

Thank you for the additional information.
The earliest that VW can look at the car is 24th April so that gives me some time to see if I can fix it first!
Have ordered an OBDeleven device.

Looks like I should be able to test the integrity of the wiring using the multimeter between pin#72, Socket A on the BCM back to the rear fog by getting access to the BCM plugs. Understand this just needs removal of glovebox lid similar to changing the pollen filter, and not removal of the whole glove box unit!
These are the Haynes Autofix diagrams for my car

Exterior lights : Estate, With bi-xenon headlights, (05/2015 - 10/2016)​

Could also then check pin #5 of the light switch socket back to pin #29 Socket A on the BCM (E6) if necessary:

Will report back on progress.

Tony

 

[DV52]

Tony: My wiring diagram was taken from a "general" Golf mk7 (Rest-of-World model), If I'm reading your "Haynes Autofix diagrams" correctly, the tail-lights on an ESTATE are wired different.

Notice on your diagram that the wire on A72 ( in "E2" box - not sure what this refers-to, but I assume that it's the collective of the 3 x BCM sockets ) is terminated ultimately on pin #1 of 0159 on this car. It's NOT terminated on pin #5 as in my wiring diagram.

Good luck!!
Don

 

[bainbad]

Still no working Rear Fog Light but OBD eleven arrived yesterday. Bit of a learning curve, but so far:

• No fault codes in Central Electronics.
• Using the Output test for Rear Fog light both the Rear Fog Light and the amber Dashboard Warning light do come on!
• Using the Live data test for Rear Fog light neither the Rear Fog Light no the amber Dashboard Warning light come on when I pull the euro switch out to the Rear Fog On position. Signal state remains as “not active”.

So presumably the problem must lie either physically between the headlight switch and the BCM or be related to the way that the BCM is coded to interpret the signal from Pin 5 of the Euroswitch?

It had a new Headlight Switch of the correct part number a few days ago and I can see no problem with the switch wiring loom.

The signal from Headlight switch pin 5 for the Rear Fog Light (no front fogs fitted) should be going to pin A29 of the BCM and telling it to turn the fog lights on. How do I check that this is correctly coded, please?

Lichtfuntion A 26 is currently set as “Nebelschlusslicht wenn kein Anhaenger gesteckt und Linksverkehr“. Deepl tells me that means “Rear fog light when no trailer is plugged in and left-hand traffic” (Car is a RHD drive UK model).

Thanks for any help that you can offer.

Tony

 

[DV52]

Tony: Because of the wiring arrangement - the rotary light switch is an input to the BCM which then supplies an output (i.e. power) to the fog-light lamp. I agree, if the OBD11 output test illuminates the rear fog-light, it means that the physical wiring/terminations to the actual lamp (i.e. downstream of the BCM) is OK.

Here's how the Leuchte-set for the rear fog-light with an incandescent lamp is factory coded (taken from a UK car in my MQB database):

Leuchte26NSL LA72
Lasttyp 26    >    9 - allgemeine Glühlampe 27W; auch H15
Lampendefektbitposition 26    >    1C
Fehlerort mittleres Byte DTC-DFCC 26    >    2F
Lichtfunktion A 26    >    Nebelschlusslicht wenn kein Anhaenger gesteckt und Linksverkehr
Lichtfunktion B 26    >    not active
Dimmwert AB 26    >    100
Lichtansteuerung HD AB 26    >    only_if_closed
Lichtfunktion C 26    >    not active
Lichtfunktion D 26    >    not active
Dimmwert CD 26    >    0
Dimming Direction CD 26    >    maximize
Lichtfunktion E 26    >    not active
Lichtfunktion F 26    >    not active
Dimmwert EF 26    >    0
Dimming Direction EF 26    >    maximize
Lichtfunktion G 26    >    not active
Lichtfunktion H 26    >    not active
Dimmwert GH 26    >    0
Dimming Direction GH 26    >    maximize

Maybe check with the values on your car - are the settings the same? Don't worry about Lichtfunktion A 26 referring to left-side on a RHD car. As I have already said, the "left" reference is nominal only

@bainbad: The signal from Headlight switch pin 5 for the Rear Fog Light (no front fogs fitted) should be going to pin A29 of the BCM and telling it to turn the fog lights on. How do I check that this is correctly coded, please?

The way that the BCM is told to start operating a rotary light swtch that has a center turret position for the rear fog-light is via the software switch on module's long-code string. As I already said in my first reply, this software switch is on Byte 07, Bit 4 - which is set on your BCM. So, I'm reasonably confident that the coding for rotary light switch is correct on this car and if the Leuchte-set values line-up, I suspect that the BCM output programming for the fog-light is OK too!

If OBD11 is showing no errors and if the live data test doesn't illuminate the fog-light (but the output test does switch on the lamps), doesn't this sequence of diagnostic outcomes suggest that the BCM isn't receiving a signal from the rotary light switch to turn-ON the fog light? Because you have tried a second rotary light switch with no success - the only piece of the electrical circuit that remains untested is the wire/terminations from the light switch to pin #A29 on the BCM connector (I think)

The blue/green wire on both our wiring diagrams is a direct connection (there are no intervening terminations) - so this is a strange fault. Nevertheless - I guess it is still possible (notwithstanding unlikely) that the wire is the problem - maybe?

Don

 

[bainbad]

Thanks Don

I have checked the output on my car from the OBD11 as per the following two screenshots. All the data looks identical to what you have posted for the Leuchte-set for the factory coded rear fog-light with an incansedcent lamp for a UK car in your MQB database.

Does this exclude the possibility of a coding error and mean that it must be a physical problem between the brand new replacement headlight switch pin 5 and pin A29 of the BCM?

Tony

 

[bainbad]

Is there a way to reboot the BCM without it losing all its coding in case it has just got a bit confused internally? Maybe after some form of reboot it would start recognising the signal from pin 5. Wishfull thinking I guess.

 

[ZERO815]

To my knowledge the MK7 hatch uses the same tailgate latch as the '14 Beetle. We had a strange trunk light behavior in our Beetle that I couldn't explain. It turned out the engaging of the micro switch wasn't working correctly any more. Replaced the latch and all is good now.

Looking at the coding of the rear fog light I noticed one line that might stop your fog light from working. Let's assume the latch in your car has a fault too, since "Lichtansteuerung HD AB 26" (HD = tail gate) is set to "only if closed" the rear fog light won't turn on if the latch doesn't signal the car that the trunk is closed. Please try "Lichtansteuerung HD AB 26" with value "Always" instead.

 

[bainbad]

Hi ZERO815

Thank your for the suggestion. I had already tried that "always" option for Lichtansteuerung HD AB 26 but had not posted it. However, I have just given it another attempt. Sadly it made no difference to the non-operability of the Rear Fog from the Headlight Switch.

 

[bainbad]

Realised that the small indicator light for the Rear Fog on the Headlight Switch doesn't ever light up even when doing a successful Output Test for the Rear Fog. So I tested fuses C34 and C8 which both supply the Headlight Switch: both intact. Had to take the glovebox lid off on the RHD car to get to the fusebox. Access to the BCM Socket A wiring did not look at all good for testing pin A72 back to pin 5 of the headlight switch.

 

[ZERO815]

The indicator light on my light switch doesn’t turn on for the rear fog either. There’s only the amber signal in the dashboard.

On my LHD MK7 I have to take the kick-panel out, the side cover of the dashboard, lower A-pillar cover between door and dashboard to have enough room and visibility to access the BCM plugs.

 

[DV52]

Is there a way to reboot the BCM without it losing all its coding in case it has just got a bit confused internally? Maybe after some form of reboot it would start recognising the signal from pin 5. Wishfull thinking I guess.

hmm..... I guess anything is possible - so worth a try!!

You could try a "total vehicle reset" - remove the +ve battery terminal connector for about 20 minutes. When you replace the battery clamp, expect a bunch of errors to be reported on the dash - don't panic this is normal, go for a short drive and the errors should re-set (this suggested procedure is electrically the same as changing a battery).

If the problem persists - this is indeed a tricky problem !! I agree with @ZERO815 - access to the 3 x BCM sockets is a bitch on a RHD vehicle (Australia is RHD too -because of our colonial masters).

Thinking out-loud about this case - it seems unlikely (albeit, still possible) that the problem is at the BCM end of the yellow/green wire. The 3 x multi-pin sockets are firmly seated into the BCM housing with little chance of moving. And as I have already said, the A29 wire is directly connected -so no intervening terminals/plugs on-route to the rotary light switch.

Of course, the unknown here is how-long this fault has persisted - but even if you don't use the rear fog -light, I assume that it operated successfully at the previous MOT test.

Because I'm a self confessed nerd - I've built a "virtual mk7" which consists of a number of key modules hooked together in spaghetti mode wiring. Fortuitously, my test-bench car includes a rotary light switch and I've also made a simulated panel for the exterior lights on a real mk7. It looks like this:

I've tried to duplicate your problem on my "virtual mk7" and my observations are as follows:

1. The OBD11 output test for the rear fog-light illuminates the actual lamps and it also lights-up the indicator light on the instrument cluster
2. If I connect a multi-meter which is set to DC Volts (full-scale 2V) with the +ve lead onto A29 pin and the negative lead on earth, I measure the following:
   
   No fog-lights (center turret in OFF position) = 1.9V
   Front fog-lights (center turret 1st position) = 0.8V
   Rear fog-lights (center turret 2nd position) = 0.2V​
3. If I remove the A29 wire on the BCM, no error messages are reported by OBD11 (go figure!!)

So, maybe an easy try might be to grab a small-thin sewing needle (emphasis on "small") and pierce the insulation on the fog-light wire at the rear of the light-switch connector. The needle needs to make contact with the copper strands in the wire - but be careful not to sever any of the strands with the needle (that's why a "small" needle is preferred).

Then duplicate my tests in 2. above. Don't expect to read exactly my values (because multi-meters reading the wave forms that I show in my previous reply will differ) - however, you should observe a drop in Volts when the center turret is pulled-out.
Don