A4 B7 Cab switching bulb error after switching to LED headlights

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avisonjohn

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I swapped my halogens to some LEDs and fitted the load resistors but still get a bulb warning.

I din think my BCM allows me to cancel the bulb warning, but hoping somebody can prove me wrong.

Does anybody know of what resistor is needed for this and I can build my own for it.

Here is an auto dump in case its needed

Code: 
Sunday,31,May,2020,18:51:33:43836
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 20.4.1.0 (x64)  HEX-V2 CB: 0.4508.4
Data version: 20200331 DS317.0
www.Ross-Tech.com


VIN: WAUZZZ8H88K013250   License Plate: 


Chassis Type: 8H (8H - Audi Cabrio B6/B7 (2003 > 2009))
Scan: 01 02 03 08 09 0F 11 15 16 17 18 25 26 36 37 45 46 55 56 57
          63 65 67 73 75 76 77
 
VIN: WAUZZZ8H88K013250   Mileage: 140950km-87582miles
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 03G-906-016-BPW.clb
   Part No SW: 03G 906 016 LQ    HW: 03G 906 016 KP
   Component: R4 2,0L EDC  000CG  1717  
   Revision: --H06---    Serial number:               
   Coding: 0000076
   Shop #: WSC 66565 257 00032
   VCID: 7DA7FCDBC1FBDD2338D-8028

No fault code found.
Readiness: 0 0 1 0 0 

-------------------------------------------------------------------------------
Address 02: Auto Trans        Labels: 01J-927-156.lbl
   Part No SW: 8E5 910 155 J    HW: 01J 927 156 HT
   Component: V30 01J 2.0l PD RdW 0040  
   Revision: 00000012    Serial number: 00000002103869
   Coding: 0000001
   Shop #: WSC 04940 001 00001
   VCID: 313F10EB4D23E943EC5-8064

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8E0-910-517.clb
   Part No SW: 8E0 910 517 H    HW: 8E0 614 517 BF
   Component: ESP8 FRONT      H06 0140  
   Revision: 00000000    Serial number: 00000000000000
   Coding: 0004402
   Shop #: WSC 63252 001 1048576
   VCID: 2C01019F6A0184ABDF3-8078

1 Fault Found:
01314 - Engine Control Module 
            013 - Check DTC Memory - Intermittent
             Freeze Frame:
                    Fault Status: 00101101
                    Fault Priority: 2
                    Fault Frequency: 4
                    Reset counter: 38
                    Time Indication: 0

             Freeze Frame:
                    Hex Value: 0x0200
                    Hex Value: 0x4A02
                    Hex Value: 0x0027
                    Hex Value: 0x01AB
                    Hex Value: 0x0000


-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 8E0-820-043.lbl
   Part No: 8E0 820 043 BL
   Component:   A4 Klimaautomat   3233  
   Coding: 00100
   Shop #: WSC 00672  
   VCID: 6C81C19FAF9144AB9F3-50F4

5 Faults Found:
00710 - Defroster Flap Positioning Motor (V107) 
            41-10 - Blocked or No Voltage - Intermittent
00601 - Potentiometer On Positioning Motor for Central Flap (G112) 
            30-00 - Open or Short to Plus
00601 - Potentiometer On Positioning Motor for Central Flap (G112) 
            09-00 - Adaptation Limit Surpassed
00735 - Potentiometer in Positioning Motor for Air recirculation Flap (G143) 
            09-00 - Adaptation Limit Surpassed
00819 - High Pressure Sensor (G65) 
            07-10 - Signal too Low - Intermittent

-------------------------------------------------------------------------------
Address 09: Cent. Elect.        Labels: 8E0-907-279-8EC.lbl
   Part No: 8E0 907 279 N
   Component: int. Lastmodul  ECE 0907  
   Coding: 20001
   Shop #: WSC 00672  
   VCID: 3D273CDB846B1D2378D-4AA4

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 8H0-959-655-94.lbl
   Part No SW: 8H0 959 655 G    HW: 8H0 959 655 G
   Component:    Airbag 9.42  H01 1840  
   Revision: 92H01184    Serial number: 003CZ0008MD7  
   Coding: 0071114
   Shop #: WSC 63252 001 1048576
   VCID: 3E253BD78C7D063B617-806A

   Subsystem 1 - Serial number: 6332BRB403876EFB2

   Subsystem 2 - Serial number: 6342BRB4038D8403L

   Subsystem 3 - Serial number: 63729RB4037B0B95T

   Subsystem 4 - Serial number: 63829RB4037B015EP

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel        Labels: 8E0-953-549.lbl
   Part No: 8E0 953 549 Q
   Component: Lenksáulenmodul     0801  
   Coding: 03111
   Shop #: WSC 00672  
   VCID: 41DF402BF89379C31C5-4AA4

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 8E0-920-9xx-8EC.lbl
   Part No SW: 8H0 920 951 D    HW: 8H0 920 951 D
   Component: KOMBI+WFS 4     H14 0200  
   Revision: 0200        Serial number: 00000000000000
   Coding: 0006411
   Shop #: WSC 56029 002 1048576
   VCID: 2E050B975C0DF6BBF17-50F4

No fault code found.

-------------------------------------------------------------------------------
Address 25: Immobilizer        Labels: 8E0-920-9xx-8EC.lbl
   Part No SW: 8H0 920 951 D    HW: 8H0 920 951 D
   Component: KOMBI+WFS 4     H14 0200  
   Revision: 0200        Serial number: 00000000000000
   Coding: 0006411
   Shop #: WSC 56029 002 1048576
   VCID: 2E050B975C0DF6BBF17-50F4

No fault code found.

-------------------------------------------------------------------------------
Address 26: Auto Roof        Labels: 8H0-959-255.lbl
   Part No: 8H0 959 255 A
   Component:  VSG  B6 CABRIO     7094  
   Shop #: WSC 00672 785 00200
   VCID: 343119FFB221DC6B873-50F4

No fault code found.

-------------------------------------------------------------------------------
Address 45: Inter. Monitor        Labels: 8E0-951-177.lbl
   Part No: 8H0 951 178 
   Component: Innenraumueberw.   0411  
   Coding: 00001
   Shop #: WSC 00000  
   VCID: 6FBBD6939E87BFB3BA1-50AE

No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv.        Labels:. 8E0-959-433-MAX.clb
   Part No: 8H0 959 433 M
   Component: Komfortgerát T3B    5442  
   Coding: 06911
   Shop #: WSC 00672  
   VCID: 3E253BD7896D063B617-4AA4

   Subsystem 1 - Part No: 8H2959802D
   Component: Tõrsteuer.FS BRM 0205  

   Subsystem 2 - Part No: 8H2959801D
   Component: Tõrsteuer.BF BRM 0205  

   Subsystem 3 - Part No: 8H0959801A
   Component: Tõrsteuer.HL BRM 0003  

   Subsystem 4 - Part No: 8H0959802A
   Component: Tõrsteuer.HR BRM 0003  

2 Faults Found:
01616 - Signal Wire to Interior Monitor 
            79-10 - Please Check Fault Codes - Intermittent
01616 - Signal Wire to Interior Monitor 
            49-10 - No Communications - Intermittent

-------------------------------------------------------------------------------
Address 56: Radio        Labels: 8J0-035-1xx-56.clb
   Part No SW: 8E0 035 186 AL    HW: 8E0 035 186 AL
   Component: R Concert2+     H02 0270  
   Revision: 00H02000    Serial number: AUZ1Z3H8971904
   Coding: 0610331
   Shop #: WSC 00672 785 00200
   VCID: 71BFD0EB8D83A943AC5-5160

No fault code found.

-------------------------------------------------------------------------------
Address 77: Telephone        Labels: 8P0-862-335.lbl
   Part No SW: 8P0 862 335 Q    HW: 8P0 862 335 Q
   Component: FSE_255x BT     H26 0350  
   Revision: 00000000    Serial number: 00000005556949
   Coding: 0001602
   Shop #: WSC 00672 785 00200
   VCID: 44D1493FE2816CEB373-50D0

No fault code found.
 
   #2  
Bruce

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What was the wattage of the bulbs removed?

Resistance = (Volts * Volts)/Watts. In this case: R=144/Watts (using nominal voltage of 12 volts) R is likely to be between 2 and 3 ohms. I'm thinking the wattage is 50-60 watts...

The resistor needs to be a 50 watt resistor that will get very hot. Keep it away from anything that can be melted or catch fire.

The LED headlight will consume some power... to see how that will modify the value of the resistor, we need to know the amps that the LED headlight draws. I know some have put 50 Watt rheostats in to set the resistance value. They are expensive. Better to make a calculation and buy a resistor of near value.

What value did you use?
 
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The LED light draws 1.6A when running on 12v, so I calculate around 19W, resulting in 7.5Ohms resistance.
The original bulbs were rated 55W @ 12v, so that would be 4.6A, and 2.6Ohms resistance.....if my maths is working correctly today...
 
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PetrolDave

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avisonjohn said:
The LED light draws 1.6A when running on 12v, so I calculate around 19W, resulting in 7.5Ohms resistance.
The original bulbs were rated 55W @ 12v, so that would be 4.6A, and 2.6Ohms resistance.....if my maths is working correctly today...
Click to expand...
So you need to add a resistor in parallel with the LED of the correct value to reduce 7.5 ohms to 2.6 ohms, the formula for this is:

R2 = (R1 * R) / (R1 - R) where R = the desired value (2.6 ohms) and R1 = the value of the LED (7.5 ohms)

So you need to add a resistor of 3.9 ohms, which just happens to be a 'standard' value! This will dissipate 37 watts, so I would suggest a 50W resistor - mounted somewhere safe and capable of dissipating the heat.
 
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PetrolDave said:
So you need to add a resistor in parallel with the LED of the correct value to reduce 7.5 ohms to 2.6 ohms, the formula for this is:

R2 = (R1 * R) / (R1 - R) where R = the desired value (2.6 ohms) and R1 = the value of the LED (7.5 ohms)

So you need to add a resistor of 3.9 ohms, which just happens to be a 'standard' value! This will dissipate 37 watts, so I would suggest a 50W resistor - mounted somewhere safe and capable of dissipating the heat.
Click to expand...

OK, it makes total sense now that you write the formula :rolleyes:
37W is a lot for it to get rid of - I can only imagine the heat coming from that thing. I'll have a rummage around the den to see if I have a suitable resistor.

Is there no way to disable this in the BCM so as to avoid having potentially hot resistors sitting in the bay?

I was also wondering, assuming the BCM only checks the lights when the ignition is turned on....could I wire up a MOSFET or I guess even a relay, so that when ignition is on, a standalone resistor is connected to the BCM instead of a bulb (via the NC), and then when I turn the headlights on, it can trigger the relay which will disconnect the resistor and flip over to the LED bulb (on the NO pin).
Would that be enough to keep the BCM from complaining about the lights?
 
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Uwe

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avisonjohn said:
Is there no way to disable this in the BCM so as to avoid having potentially hot resistors sitting in the bay?
Click to expand...
On that old CECM? I don't think so. It is an early 2000's, or maybe even late 1990s design.

avisonjohn said:
I was also wondering, assuming the BCM only checks the lights when the ignition is turned on....could I wire up a MOSFET or I guess even a relay, so that when ignition is on, a standalone resistor is connected to the BCM instead of a bulb (via the NC), and then when I turn the headlights on, it can trigger the relay which will disconnect the resistor and flip over to the LED bulb (on the NO pin).
Would that be enough to keep the BCM from complaining about the lights?
Click to expand...
You have the car, so you're in a better position to test that assumption than those of us without such a car. ;)

-Uwe-
 
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Have just tested the 'resistor' that I had already purchased, and was getting some very odd resistance readings from it, which led me to believe that it wasnt really a resistor inside.
Busted it open, and it's essentially a large capacitor and a few IC's. I'll desolder all of that and install my own resistor in it's place and reassemble.
Soon as I'm done, I'll post up the results and let you know.
Will also look at building the relay system mentioned above let you all know how that works :)
 
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avisonjohn said:
Will also look at building the relay system mentioned above let you all know how that works :)
Click to expand...

It will not work. System is designed in a way that current flowing to bulbs is monitored all the time, not only for some seconds after ignition on. You can test it in a simple way: reinstall the original halogen bulbs - no warning on dash. Keep the ignition on (or engine running) and headlights on and remove connector from one bulb - warning will appear on dash ;)
P.S. Just in case post an admap of Your 09 module.
 
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Update - according label file only fog lights diagnosis (bad bulb warning) can be enabled/disabled in this module...
 
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MartinsX said:
It will not work. System is designed in a way that current flowing to bulbs is monitored all the time, not only for some seconds after ignition on. You can test it in a simple way: reinstall the original halogen bulbs - no warning on dash. Keep the ignition on (or engine running) and headlights on and remove connector from one bulb - warning will appear on dash ;)
P.S. Just in case post an admap of Your 09 module.
Click to expand...
Yep, done that about an hour ago and noticed it comes up, which puts a bit of a downer on things :/
Have ordered some new resistors so will get some wires soldered to them and attach to the loom in an inconspicuous place in the engine bay instead.

MartinsX said:
Update - according label file only fog lights diagnosis (bad bulb warning) can be enabled/disabled in this module...
Click to expand...
Bugger, but thank's for checking
 
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PetrolDave

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MartinsX said:
Update - according label file only fog lights diagnosis (bad bulb warning) can be enabled/disabled in this module...
Click to expand...
That's there because one variant (DTM Edition) was available without front fog lights ;)
 
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Well, I went ahead and created a new harness with a brand new 100W resistor in place, and it worked, but even at 100W, it got so damn hot that I decided to just uninstall it.

Can anybody recommend any alternative lamps in place of white LED's, which will not give any issues, short of retrofitting the Xenon headlamps?
 
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FYI, european cars came with LED headlights. Utilizing byte 18 of the CECM you can get where the headlights don't throw a CEL. I have experimented and was able to get it to work, however, it requires some modification to get rid of a rear fog light that the european cars have.
 
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siLc

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RoW Audi A4 B7 with LED headlights from the factory? Highly unlikely. You sure you’re not confusing it with the RoW Passat B7 which has LED running lights and byte 18 lights config?
 
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PetrolDave

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rhill2901 said:
FYI, european cars came with LED headlights.

Utilizing byte 18 of the CECM
Click to expand...
Having owned several European Audi B7 A4 cars I can categorically state that is wrong - the only options were Halogen or HID headlamps.

Not surprising when you remember than the B7 A4 ceased production in 2008 - before LED headlamps were available.

Also the B7 A4 was never fitted with a CECM that had Long Coding, so there is no byte 18 to modify.
 
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ok, my apologies. speaking from a vw mk6 jetta experience.
 
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PetrolDave said:
Having owned several European Audi B7 A4 cars I can categorically state that is wrong - the only options were Halogen or HID headlamps.

Not surprising when you remember than the B7 A4 ceased production in 2008 - before LED headlamps were available.

Also the B7 A4 was never fitted with a CECM that had Long Coding, so there is no byte 18 to modify.
Click to expand...

Is it possible to replace with one that does allow the Long Coding to be changed?
 
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Uwe

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avisonjohn said:
Is it possible to replace with one that does allow the Long Coding to be changed?
Click to expand...
Doing so would involve a substantial amount of re-wiring because you'd need to use a module from a completely different car. This is not something I've ever heard of someone doing on a B7. Then even if you got it wired in, the question is how happy would it and the other systems it's networked to in your car be about such a mis-match?

-Uwe-
 
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Bit of an epic thread revivial, but I did just want to comment on this..

Is everyone here making a bad and potentially dangerous assumption that the current draw of the resistor would need to be the same as the original bulbs?
Surely the electronics would be testing for some current draw, and not necessarily the same amount as an original bulb??

I actually found this thread because Im considering putting LED indicators in my rear, after many years one of my globes has blown and I was just looking to see if someone hasgone as far as working out the biggest resistor value that would still fool the electronics.
Here's the catch .. I already installed load resistors for my number plate lights yyeeaarrss ago .. I just couldn't remember what value I originally used... but I took a pretty high resistance so that it is dissipating "not as much" heat like an original globe!
It was still a chunky ceramic white type resistor, and I placed it with some white heat transfer compound and mounted them flush against my boot lid so that large object is also dissipating the heat.. but I only did this just to really go over the top - it only ever got "warm" from memory.

I never, ever had them "so hot" that you couldn't touch them.. that's insane..

I will post here again the value of the resistor that I used .. because I will be reviewing my work on my car.. But I just wanted to post my opinion on this to avoid , or steer someone else away from the path of thinking you need the same current drain and red hot resistors in their car is a good idea.. far out. Scary.
 
   #20  
PetrolDave

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LooseCannon said:
Is everyone here making a bad and potentially dangerous assumption that the current draw of the resistor would need to be the same as the original bulbs?
Surely the electronics would be testing for some current draw, and not necessarily the same amount as an original bulb??
Click to expand...
The bulb failure system does 2 types of testing:
- cold diagnosis (is there a bulb present?)
- hot diagnosis (is the bulb drawing sufficient current when on?)

Without access to the VAG software (and maybe hardware too) it's impossible to know what the maximum resistance is for the bulb failure system to be 'happy' in both situations.

So the two options seem to be:
- A, draw the same current as an incandescent bulb
- B, spend some time experimenting with gradually decreasing values of resistance until the warnings go away (note this is very likely to be ambient temperature dependent too).

So people tend to go for the 'safe' option A as it's less hassle then option B. Option A can never be bad, but if the resistors (which will get hot) are not suitably situated to deal with the heat dissipation could be a smoulder/fire risk - which is something that I personally always advise about.
 
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