LED Bulb Coding - License Plate Light Without Pulse Width Modulation Option

[GaryM]

In preparation for replacing the license plate incandescent bulbs in my car with LED bulbs instead, I thought it would probably be a good idea to actually test the switching off of the "Lamp Monitoring (Cold) License Plate Lamps active" option first which on my 5K0937087R BCM is Bit 6 of Byte 23...

This I have proven to work just fine. If this coding option is active (factory default) and I remove both bulbs, the "bulb out" warning indicator comes on and I get told in my MFD that the offending bulbs are the license plate ones. If I deactivate the coding option and clear the fault codes, with no license plate bulbs fitted I get no recurring "bulb out" warning. Just what I need to happen so this is good news

So onto my next question regarding the other related license plate bulb coding value. This is Bit 7 of Byte 17 and is labelled "License Plate Light w/o Pulse Width Modulation (PWM) [LED Light]" (see screenshot below). The very end part in brackets suggests that I probably need to activate this option if I am going to be fitting LED bulbs (i.e switch off PWM). The question I have is do I actually need to activate this for LED bulbs, and if so then why exactly?

I understand that PWM is used to control the brightness (dimming) of incandescent bulbs, but what about controlling the brightness of LEDs? This can also be achieved with PWM so I'm not quite sure I understand why PWM would not be required for LED bulbs. If PWM is left switched on, would there be any detrimental effects of this on an LED bulb or the lighting circuit of the BCM itself?

 

[Uwe]

I don't suppose you have an oscilloscope to see exactly what the PWM does?

While it's certainly possible to control the brightness of LEDs using PWM, it has to be done at a higher frequency than with incandescent bulbs to avoid visible flicker because LEDs turn on and off almost instantly compared to incandescent bulbs (due to the thermal inertia of the filaments in the latter).

I suspect PWM is done with incandescent bulbs to keep them at close to an effective 12V, even when bus voltage is up around 14V, in order to extend their life.

-Uwe-

 

[Blackfrosch]

You need to change both options to make sure you do not get a warning in your dash. On some PQ35 the LED-option does not work, until you update the bcm module.

greatings

 

[GaryM]

I don't suppose you have an oscilloscope to see exactly what the PWM does?

Yes I do have actually have an oscilloscope although it's a mains powered one so it just means I'll need to reel out the extension lead. TBH it didn't even cross my mind to scope the output in each of the two modes so maybe I'll try and find some time do that and then post back the results once I've done that.

While it's certainly possible to control the brightness of LEDs using PWM, it has to be done at a higher frequency than with incandescent bulbs to avoid visible flicker because LEDs turn on and off almost instantly compared to incandescent bulbs (due to the thermal inertia of the filaments in the latter).

Do you happen to know if the CAN BUS specific LED bulbs circumvent against such flickering issues? I've been unable to find a definitive answer on what differs between the "CAN BUS" LEDs and the "non CAN BUS" LEDs. I guess both will contain voltage regulator circuitry to step down the 12v to 5v (or 3.3v) and the "error free" CAN BUS ones will additionally have built in load resistors to fool the bulb check system into thinking incandescent bulbs are still fitted, but what about LEDs that are marketed as "CAN BUS" ones but don't claim to be error free? I wonder what is so special about those over ones that are marketed as "non CAN BUS" LEDs?

I suspect PWM is done with incandescent bulbs to keep them at close to an effective 12V, even when bus voltage is up around 14V, in order to extend their life.

Is that not what Byte 19 is for? My fronts seem to be set to 13.0V and my rear ones seem to have no restriction. These are both factory settings that I've not messed with. I'm not entirely sure why there would be a difference in settings between front and rear unless it's because my rear light clusters contain some LED lights (stop and position lights that are built into the factory cluster) and some are incandescent bulbs (turn signals, reverse, and fog lights).

 

[Sebastian]

There are no CAN-Bus LEDs! What is offered under that term (which is beyond misleading), are LEDs with a series resistor - no more, no less. That said, some of the discrepencies you're seeing with the coding table is based on the fact that the original table applies to Helly (1K0) BCMs and is not 100% identical for Continental (5K0) BCMs - in addition there are variations based on the control module firmware version, which we are currently not taking into account.

 

[GaryM]

You need to change both options to make sure you do not get a warning in your dash. On some PQ35 the LED-option does not work, until you update the bcm module.

I already did a test with the incandescent bulbs removed (i.e. no bulbs fitted at all) and with just the "Lamp Monitoring (Cold) License Plate Lamps active" option switched OFF and the "License Plate Light w/o Pulse Width Modulation (PWM) [LED Light]" left switched OFF (factory default) I was NOT getting a "bulb out" error.

Or are you saying that if I was to fit LED bulbs, I would then actually see the "bulb out" error reappear unless I was to also switch ON the "License Plate Light w/o Pulse Width Modulation (PWM) [LED Light]" option?

I guess I'll find out for certain when I've actually got some LED bulbs.

 

[GaryM]

There are no CAN-Bus LEDs! What is offered under that term (which is beyond misleading), are LEDs with a series resistor - no more, no less.

Thanks Sebastian. That is exactly what I was trying to find out but there seems to be so much misinformation on the internet that it is almost impossible to find a definitive answer.

So basically the bottom line is that all "CAN-Bus" LEDs should actually be error free whether they explicitly claim to be or not, as long as the load resistor meets the current draw requirements of the bulb check circuitry for the BCM to which the bulb is connected.

If I switch off cold diagnostics on the license plate bulbs, am I therefore correct in saying that I have no need for "CAN-Bus" LEDs and can just get normal LEDs (non CAN-Bus) designed for automotive applications without the risk of doing any damage to the BCM? I see no point in drawing excessive current and generating unnecessary heat if there is no need to with the cold diagnostics switched off.

 

[jasons6930]

FWIW, my 2017 Caddy has stop and tail lights via dimming.

I have just installed some can friendly rear 382 indicator leds and they work fine with no error.

Now, as it is the same lamp base as the stop/tail, i fitted it to that socket and whilst the brake light function worked, it did not dim down for the tail light function, in fact it didn't work at all. When i turned the lights off and removed the key the CH lights activated and the LED bulb that was still left connected started to exhibit a very faint flicker.

I was then pointed to this lamp that should work, however, it does state that it is not an error free lamp so ill see what happens when it gets here from across the pond!

https://www.amazon.com/gp/product/B00HWS7TRK/ref=od_aui_detailpages00?ie=UTF8&psc=1

Also, i'll post up some screen shots of my codes for comparison if you like

 

[Sebastian]

I have yet to find a single LED with series resistor which is certified, meaning all the ones I have seen so far will make your car illegal on the streets. Since the UK is still part of the EU for the time being, I am also assuming this is the case for you guys.

 

[Uwe]

LEDs with a series resistor - no more, no less.

LED with series resistor

Hmm, if I were trying to get an LED light module to simulate the load presented by an old-school incandescent bulb, I would put the resistor in parallel with it, not in series.

-Uwe-

 

[jasons6930]

Yes they probably are illegal, although i'm not sure would make the LED lamps legal?

There are plenty of vehicles out there now with OEM LED rear lights that are very bright.

The signal lamps that i have fitted are virtually identical in brightness to a standard filament lamp.


Anyway, i checked my codings and mine is exactly the same as GaryM.

However, when i did an autoscan, it showed a fault in the lamp location where i tried the LED lamp as a short circuit.

So, with that in mind, legalities aside, i would say that leaving the settings at default and using a good quality LED lamp, the circuitry will not dim the LED.

Having said that, i will still give the Philips ones a go when they arrive and report back.

 

[GaryM]

I have yet to find a single LED with series resistor which is certified, meaning all the ones I have seen so far will make your car illegal on the streets. Since the UK is still part of the EU for the time being, I am also assuming this is the case for you guys.

Keep in mind that UK legislation for vehicle lighting hasn't had any changes to it since 1989 so you probably won't be surprised to hear that everything regarding approval markings refers to "filament" bulbs with no mention at all about either LED or HID/Xenon discharge gas lighting because neither had been invented at that point in time. However, if you tried to argue the toss in court because your car has LED bulbs and not "filament" bulbs, I'm not sure if you would come out of it unscathed If you're interested, the legalities are under The Road Vehicles Lighting Regulations 1989, Regulation 14 HERE.

The UK MOT which is equivalent of the German TÜV but far less strict also has no mention of the test requiring the MOT'er to check any bulbs for approval markings. It is just a visual check to ensure that all light bulbs are working and are of a white or yellow colour, with a machine check to ensure that main beams headlights are correctly aligned (details HERE).

That probably explains why we have thousands of cars driving around in the UK with Chinese manufactured aftermarket LED bulbs fitted to them, none of which have any type of approval whatsoever, and where no-one in authority so much as bats an eyelid at them.

 

[GaryM]

Anyway, i checked my codings and mine is exactly the same as GaryM.

However, when i did an autoscan, it showed a fault in the lamp location where i tried the LED lamp as a short circuit.

So, with that in mind, legalities aside, i would say that leaving the settings at default and using a good quality LED lamp, the circuitry will not dim the LED.

Having said that, i will still give the Philips ones a go when they arrive and report back.

The only foolproof way to fit LEDs in place of incandescent bulbs and stop the "bulb out" warning indicator being triggered is to completely turn off the bulb diagnosis check circuits. Doing that then avoids the need to use dummy resistors to unnecessarily load the circuit and in theory you should just be able to use cheap(ish) automotive LEDs without needing to bother with any of the CAN Bus specific ones or any fancy expensive types like the ones you posted a link to.

On some of the older BCMs you used to be able to turn off the bulb cold diagnosis checks under Byte 18 (see screenshot below) but for the newer PQ35 BCMs, the coding for Byte 18 changed to pre-defined lighting schemes which if changed can completely ruin your lighting system so it's a minefield to be avoided unless you know exactly what you are doing. On the newer PQ35 BCMs you can only disable the cold diagnosis checks for the license plate bulb circuit as shown in the screenshots of post #1 of this thread. If you want to switch off cold bulb diagnosis for other bulb circuits then you need to use another diagnostics tool that has the ability to directly edit EEPROM values in the BCM because VCDS is (purposely) unable to do that. This is what I will be doing next after I've changed the and coded the license plate bulbs to use LED bulbs. Baby steps first

 

[jasons6930]

Yes i think EEPROM is something that i will stay away from, and make do with trying various LED bulbs to see what works etc.

As usual with VW, they are taking more and more away from the home enthusiast and independent repair workshops to try and keep it all in house.

 

[DV52]

I understand that PWM is used to control the brightness (dimming) of incandescent bulbs, but what about controlling the brightness of LEDs? This can also be achieved with PWM so I'm not quite sure I understand why PWM would not be required for LED bulbs. If PWM is left switched on, would there be any detrimental effects of this on an LED bulb or the lighting circuit of the BCM itself?

Gary: As usual, your post raises some very interesting questions! I'm not sure about the details of the system for dimming control in your particular car, but I can describe my findings for how lamp dimming seems to work on VW cars that use Leuchte channels - I suspect that the fundamentals are the same, regardless of vehicle.

As you may be aware, Leuchte channel control can accommodate both incandescent and LED lamps and PWM is used for dimming - like your car. Also, it's possible to select the exact degree of lamp dimming (0-100 for incandescent & 0-127 for LED) - not sure if this is the same in your car.

Here is the voltage trace for an output lamp pin on the BCM with the leuchte channel set for a LED lamp and with a dimming level selection of 50%:

Notice that despite the 50% dimming level, the duty cycle of the wave-form is actually more like 60%. What appears to happen is that the duty cycle of the square wave above 100 (for LED settings) doesn't change - so I assume that something else happens (perhaps the current waveform alters) at settings from 100-127.

Notice also that the waveform frequency is 200 Hz (i.e. 50 msec). With Leuchte channels, it's possible to select specific settings to accommodate a large variety of LED lamp types (i.e. different wattage) and its also possible to select these lamps for differing applications (i.e. turn-signal, bakes etc). However, regardless of the selection, the same 200 Hz frequency appears to apply and it seems that the wattage type selection changes the dimming/duty cycle variance of the waveform - albeit there are only a few allowable variances- so LED wattage selection is bunched together into these few options.

If an incandescent lamp type is selected (instead of LED) - what appears to happen to the voltage trace is that the PWM frequency is halved (i.e. the time-base of the waveform is more like 10 msec) and the duty cycle of the square wave is more linear with the dimming level.

So, moral of the story is yes- indeed PWM is an acceptable method of dimming control for LEDs on VW vehicles (at least where Leuchte channels are concerned).

Don

PS: I haven't as yet investigated what happens to the waveform of the electrical current to these lamp type settings, As you probably already know, LEDs are current devices, rather than voltage devices, so this is probably more important for your question . I'm not sure if the PWM capability of the BCM has a current limiting function (I suspect that it does -given that Leuchte channel BCM s don't use in-line fuses), or if the operation is more simplistic (as Uwe has suggested in a previous response). Something to look-at later when time allows

 

[jasons6930]

As an update to this, i tried a different can friendly LED single contact lamp in the stop/tail socket.

As you will see from the video, when the lamp is turned on from the switch, it is very, very dim, however, if i put my foot on the brake pedal it goes to full brightness, but then if i take my foot off, it stabilises at a dimmer output for tail light duties and seems stable.

I will do a scan later and see what faults it throws back.

Please excuse the diabolical quality of the video

I guess the flickering is the frame rate of the awesome iPhone7 as it does not do it to the naked eye.

Ok here is the scan, which shows no faults logged.

However, this time, I tried the lamp in the passenger side, but i will admit, that when i tried an LED before that threw up faults, it was a different colour (amber) and was on the drivers side, but was exactly the same make and model.

No coding or changes were made with settings and are left as factory default.

If anyone has any suggestions as to how to make them energise properly from start up (dimmed) it would be appreciated.

Or, if anyone would like me to try some changes in VCDS, i'm happy to do that, although nothing too tech please!

Saturday,06,May,2017,17:33:52:35443
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 17.1.3.0 (x64)  HEX-V2 CB: 0.4336.4
Data version: 20170320 DS267.7
www.Ross-Tech.com


VIN: WV1ZZZ2KZHX100354   License Plate: SCAN1
Mileage: 2810km-1746mi   Repair Order: 



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 2K (7N0)
Scan: 01 03 08 09 10 13 15 16 17 19 25 42 44 46 52 5F 61

VIN: WV1ZZZ2KZHX100354   Mileage: 2810km-1746miles

01-Engine -- Status: OK 0000
03-ABS Brakes -- Status: OK 0000
04-Steering Angle -- Status: OK 0000
08-Auto HVAC -- Status: OK 0000
09-Cent. Elect. -- Status: OK 0000
10-Park/Steer Assist -- Status: OK 0000
13-Auto Dist. Reg -- Status: OK 0000
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: OK 0000
17-Instruments -- Status: OK 0000
19-CAN Gateway -- Status: OK 0000
25-Immobilizer -- Status: OK 0000
42-Door Elect, Driver -- Status: OK 0000
44-Steering Assist -- Status: OK 0000
46-Central Conv. -- Status: OK 0000
52-Door Elect, Pass. -- Status: OK 0000
5F-Information Electr. -- Status: OK 0000
61-Battery Regul. -- Status: OK 0000
-------------------------------------------------------------------------------
Address 01: Engine (J623-DFSB)       Labels: 04L-907-309-V1.clb
   Part No SW: 04L 906 016 HB    HW: 04L 907 309 K
   Component: R4 2,0L EDC   H20 1802  
   Revision: 8AH20---    
   Coding: 01190032044515090000
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_ECM20TDI01104L906016HB 001003
   ROD: EV_ECM20TDI01104L906016GR_VN35.rod
   VCID: 70BAD99CEA2BB4B7DD9-8024

No fault code found.
Readiness: 0 0 0 0 0 

-------------------------------------------------------------------------------
Address 03: ABS Brakes (J104)       Labels: Redir Fail!
   Part No SW: 7E0 907 379 P    HW: 7E0 907 379 M
   Component: ESC           H06 0133  
   Revision: 00000000    Serial number: 40107000000821
   Coding: 1079409BB262B47E0878027B4D862DE379F5F0
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_Brake1ESCCONTIVN75XGP2 011001
   ROD: EV_Brake1ESCCONTIVN75XGP2_011_VN35.rod
   VCID: 3FD84AA0E7F51BCF143-806A

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC (J255)       Labels: 5K0-907-044.clb
   Part No SW: 1K8 907 044 CH    HW: 1K8 907 044 CH
   Component: Climatronic   H08 0405  
   Revision: 00001K06    
   Coding: 0510004003
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_Climatronic A01010
   ROD: EV_ClimaAutoBasis_VW32.rod
   VCID: 77A8E2808F45E38F1C3-8022

No fault code found.

-------------------------------------------------------------------------------
Address 09: Cent. Elect. (J519)       Labels: 1K0-937-08x-09.clb
   Part No SW: 5K0 937 086 AA    HW: 5K0 937 086 AA
   Component: BCM PQ35 M+   122 0184  
   Revision: BD122001    
   Coding: 491A58F88025E16A088800809100896C037D000862208760E484C7000041
   Shop #: WSC 35110 377 08192
   VCID: 73B0D6909BBD8FAF20B-8026

   Subsystem 1 - Part No: 2K2 955 119 D  Labels: 1KX-955-119.CLB
   Component: Wischer 02011  26  0512 
   Coding: 009F95

   Subsystem 2 - Part No: 5K7 955 559 C  Labels: 5K7-955-559.CLB
   Component: RLS 211216 04  42  0106 
   Coding: 0228DD

   Subsystem 3 - Part No: 7N0 951 172 
   Component: Sensor, DWA 0  005 0502 
   Coding: 000000

   Subsystem 4 - Part No: 1K0 951 605 F
   Component: LIN BACKUP HO  H01 0008 
   Coding: 000000

No fault code found.

-------------------------------------------------------------------------------
Address 10: Park/Steer Assist (J791)       Labels: 5Q0-919-298.clb
   Part No SW: 1K8 919 475 D    HW: 5Q0 919 298 
   Component: PARKHILFE PLA H12 0480  
   Revision: --------    Serial number: 39431634901859
   Coding: 0131061041
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_EPHVA2CVW364GP00 001010
   ROD: EV_EPHVA2CVW364GP00.rod
   VCID: 3B203EB0F3ED07EF38B-806E

No fault code found.

-------------------------------------------------------------------------------
Address 13: Auto Dist. Reg (J428)       Labels: 7N0-907-572.clb
   Part No SW: 7N0 907 572 C    HW: 7N0 907 572 
   Component: ACC Bosch PQx H03 0211  
   Serial number: 04011704388226
   Coding: 00000000FE0339
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_ACCBEGVW361 001006
   ROD: EV_ACCBEGVW361.rod
   VCID: 36362F84C8CFDA87C75-8062

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags (J234)       Labels: 5K0-959-655.clb
   Part No SW: 2K5 959 655 B    HW: 2K5 959 655 B
   Component: VW10Airbag00K H08 0018  
   Revision: --------    Serial number: 003V1002FW42
   Coding: 00000000000000000000000000000000304B
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_AirbaVW10BPAVW12X 001028
   ROD: EV_AirbaVW10BPAVN750.rod
   VCID: 3B203EB0F3ED07EF38B-806E

   Crash sensor for side airbag: driver side: 
   Serial number: 3497ARB4004597JCVK9J

   Crash sensor for side airbag: front passenger side: 
   Serial number: 3507ARB401457GMESAUW

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel (J527)       Labels: 5K0-953-569.clb
   Part No SW: 5K0 953 521 GE    HW: 5K0 953 569 BF
   Component: LENKS.MODUL   018 0230  
   Revision: FF010042    Serial number: 20170103301131
   Coding: 1082C60008
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_SMLSNGVOLWSR8C 001001
   ROD: EV_SMLSNGVOLWSR8C.rod
   VCID: 75B4E8889549919F0EF-8020

   Multifunction steering wheel control module: 
   Subsystem 1 - Part No SW: 2K0 959 442 A    HW: 2K0 959 442 A  Labels: 3C8-959-537.CLB
   Component: E221__MFL-TAT  H06 0023 
   Serial number: 0021719505201432BC1B
   Coding: 2C0000

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments (J285)       Labels: 5K0-920-xxx-17.clb
   Part No SW: 2K5 920 976 E    HW: 2K5 920 976 E
   Component: KOMBI         H03 1104  
   Serial number: 00000000000000
   Coding: 410E021200
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_Kombi_UDS_VDD_RM09 A05733
   ROD: EV_Kombi_UDS_VDD_RM09_VN35.rod
   VCID: 382A21BCC2DB2CF7D59-806C

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway (J533)       Labels: 7N0-907-530-V2.clb
   Part No SW: 7N0 907 530 BL    HW: 7N0 907 530 AN
   Component: J533  Gateway H56 1682  
   Revision:   H56       Serial number: 081216F1002876
   Coding: 357431
   Shop #: WSC 35110 377 08192
   VCID: 7BA0FEB0B3EDC7EF78B-802E

No fault code found.

-------------------------------------------------------------------------------
Address 25: Immobilizer (J334)       Labels: 5K0-920-xxx-25.clb
   Part No SW: 5K0 953 234     HW: 5K0 953 234 
   Component: IMMO          H03 1104  
   Serial number: 00000000000000
   Coding: 000000
   Shop #: WSC 00000 000 00000
   ASAM Dataset: EV_Immo_UDS_VDD_RM09 A03710
   ROD: EV_Immo_UDS_VDD_RM09_VW21.rod
   VCID: 6A8ECBF4CCF74E6793D-803E

No fault code found.

-------------------------------------------------------------------------------
Address 42: Door Elect, Driver        Labels: None
   Part No SW: 2K5 959 701 A    HW: 2K5 959 701 A
   Component: Tuer-SG         009 2144  
   Coding: 0135730
   Shop #: WSC 35110 377 08192
   VCID: 323E13942827C6A7EBD-8066

No fault code found.

-------------------------------------------------------------------------------
Address 44: Steering Assist        Labels: 1K0-909-14x-GEN3.clb
   Part No: 1K0 909 144 R
   Component: EPS_ZFLS Kl. 314    3501  
   Revision: 00H22000    
   Shop #: WSC 46612 001 1048576
   VCID: 392C24B8F55135FF2A7-806C

No fault code found.

-------------------------------------------------------------------------------
Address 52: Door Elect, Pass.        Labels: None
   Part No SW: 2K5 959 702 A    HW: 2K5 959 702 A
   Component: Tuer-SG         009 2144  
   Coding: 0135730
   Shop #: WSC 35110 377 08192
   VCID: 33301690D73DCFAFE0B-8066

No fault code found.

-------------------------------------------------------------------------------
Address 5F: Information Electr. (J794)       Labels: 5G0-035-MIB-STD2.clb
   Part No SW: 5C0 035 680 E    HW: 5C0 035 680 E
   Component: MU-S-ND-ER    H31 0359  
   Serial number: VWZAZ2T5016940
   Coding: 063307013C00000011111101008808001F0100C600200100CF
   Shop #: WSC 35110 790 50316
   ASAM Dataset: EV_MUStd4CTSAT 001022
   ROD: EV_MUStd4CTSAT_SK25.rod
   VCID: 2310E6D06B5D5F2F10B-8076

   Data medium: 
   Subsystem 1 - Part No SW: 3G0 919 866 AQ    HW: -----------
   Component: ECE1 2017  --- 0730 
   Serial number: --------------------

No fault code found.

-------------------------------------------------------------------------------
Address 61: Battery Regul. (J840)       Labels: 1K0-907-534.clb
   Part No SW: 7N0 907 534     HW: 7N0 907 530 AN
   Component: Batt.regelung H56 1682  
   Serial number: 081216F1002876
   Coding: 030F7873
   Shop #: WSC 35110 377 08192
   VCID: 71BCDC98E1A1BDBFD27-8024

   Subsystem 1 - Part No SW: 2K0 915 181     HW: 2K0 915 181 
   Component: J367-BDMConti  H03 1050 
   Serial number: 75410603001701093018

No fault code found.

End----------(Elapsed Time: 01:10, VBatt start/end: 12.1V/12.1V)-----------

 

[GaryM]

Gary: As usual, your post raises some very interesting questions! I'm not sure about the details of the system for dimming control in your particular car, but I can describe my findings for how lamp dimming seems to work on VW cars that use Leuchte channels - I suspect that the fundamentals are the same, regardless of vehicle.

Don, that's some impressive analysis work you've done there so kudos to you for doing that

On the PQ35 platform cars there doesn't appear to be as much granular control over dimming of bulbs as there is on the MQB platform cars. I've found the configuration values for dimming of all the bulbs on the PQ35 platform car with exception of the license plate bulbs. The other bulbs can be dimmed by adjusting certain EEPROM memory cell byte values but I have yet to locate/confirm the memory cells that store the configuration for the license plates. While VCDS has available coding values for cold diagnosis and PWM for the license plate bulbs on the PQ35 BCMs, there is no setting that I can find for the dimming control of them so that would need to be done with EEPROM memory cell editing. I thought the license plate bulb configuration was stored under addresses 1963-1965 but I'm not so sure that is the case for my particular BCM. I will need to do some further (careful) research and analysis to try and confirm or deny this.

 

[GaryM]

Ok here is the scan, which shows no faults logged.

However, this time, I tried the lamp in the passenger side, but i will admit, that when i tried an LED before that threw up faults, it was a different colour (amber) and was on the drivers side, but was exactly the same make and model.

No coding or changes were made with settings and are left as factory default.

If anyone has any suggestions as to how to make them energise properly from start up (dimmed) it would be appreciated.

Or, if anyone would like me to try some changes in VCDS, i'm happy to do that, although nothing too tech please!

I think the only real solution is to make the necessary configuration adjustments by switching off both cold and warm diagnosis on the bulbs, and changing the bulb type configuration bit value to be for a non-incandescent bulb which I believe turns off PWM and may well be what is causing your problem. However, as previously said, there is nothing you can do in VCDS to sort out your problem unfortunately and you can only make such configuration changes by editing memory cell values in the EEPROM of the BCM.

Other than doing that, you are in minefield territory of trial and error along with potentially wasted money until you can find some CAN Bus LEDs with built in load resistors that do actually work acceptably with your particular vehicle. The newer BCMs unfortunately seem to be far more sensitive and picky about LED bulbs being fitted to an circuit that is configured for incandescent bulbs than the older BCMs used to be.

 

[jasons6930]

Ill try the cold and warm diagnostic settings tomorrow and report back.

TBH, i don't mind spending a few quid in the name of research, especially if i can get a result without having to get into complicated and hazardous hard coding

 

[GaryM]

Ill try the cold and warm diagnostic settings tomorrow and report back.

I thought it was the rear position / brake light bulb you are trying to use LED bulbs for(?) If so then I think you will be out of luck unfortunately because you have a PQ35 M+ (5K0937086AA) BCM in your Caddy which looking at your long coding value appears to use predefined lighting schemes that has Byte 18 masked with a value of "00". This means that you will have no ability to switch off cold diagnosis for the individual lighting circuits (other than for the license plate circuit) using VCDS. Please post up a screenshot of the Long Coding Helper window for Byte 18 of your BCM for clarification.

This is the Byte 18 (highlighted in red) in the long coding value of your BCM...

Address 09: Cent. Elect. (J519)       Labels: 1K0-937-08x-09.clb
   Part No SW: 5K0 937 086 AA    HW: 5K0 937 086 AA
   Component: BCM PQ35 M+   122 0184  
   Revision: BD122001    
   Coding: 491A58F88025E16A088800809100896C037D000862208760E484C7000041
   Shop #: WSC 35110 377 08192
   VCID: 73B0D6909BBD8FAF20B-8026