Code out reverse light bulb check ?

I fitted some Led reverse light bulbs into my 2009 A6 C6 avant.

There is no error on the dash but from the rear you can see them pulse every 30 seconds or so when the car performs a bulb check - can the check be coded out with VCDS or do I need to wire in a capacitor/resistor

Would be grateful for any advice - thanks

I don't see any way to do that in your CCM (the module that controls the tail lights in your car):

andyha2000 said:

Code:

-------------------------------------------------------------------------------
Address 46: Central Conv.        Labels:. 4F0-910-289.lbl
   Part No SW: 4F0 910 289 J    HW: 4F0 907 289 J
   Component: Komfortgeraet   H27 0220  
   Revision: 02200027    Serial number: 01171317770000
   Coding: 0140027
   Shop #: WSC 02335 785 00200
   VCID: 31692048A8B82BC726-8064

   Subsystem 1 - Part No: 1K0 951 605 C
   Component: LIN BACKUP HORN H03 1301

   Subsystem 2 - Part No: 4F0 910 177 
   Component: Innenraumueberw.H01 0020

No fault code found.

Click to expand...

Modules used in the 4F chassis were designed before white LED bulbs were a thing.

-Uwe-

Okay thank you - I will wire in a capacitor/resistor to try and cure the problem

andyha2000 said:

Okay thank you - I will wire in a capacitor/resistor to try and cure the problem

Click to expand...

Why a capacitor?

I've only ever used a resistor in parallel with the LED to draw enough current to fool the bulb failure detection mechanisms for cold and hot bulbs.

PetrolDave said:

Why a capacitor?

Click to expand...

If the module insists on doing "cold diagnostics" it will send short pulses to the bulb even when the bulb is off. They're short enough that a tungsten filament won't heat up enough to produce light, but an LED bulb will produce a visible flash. A capacitor will presumably absorb the pulse? I'm thinking an inductor might be a more elegant way?

-Uwe-

Uwe said:

If the module insists on doing "cold diagnostics" it will send short pulses to the bulb even when the bulb is off. They're short enough that a tungsten filament won't heat up enough to produce light, but an LED bulb will produce a visible flash. A capacitor will presumably absorb the pulse? I'm thinking an inductor might be a more elegant way?

Click to expand...

Good point

If the resistance of the driver in the BCM and the cables connecting it to the bulb are high enough the capacitor will charge up and prevent/reduce the LED from lighting.

An inductor would be more elegant, and less reliant on the value of the driver & cable resistance, but would require cutting wires.

I sometimes fitted a capacitor to avoid a relay from clicking itself (and my eardrums) to death. But then I remembered the existence of diodes, that made life even better.

^^^^ hmm.... please explain?

I get Uwe and Dave's discussion about adding Capacitor/Inductor into the lamp ciruit to produce a time delay that will filter out high frequency diagnosis pulses and I assume that the diode in your relay situation was used in "freewheeling mode"

But I'm desperately trying to understand how a diode might be useful in Andy's LED situation - as I'm sure you already know, freewheeling diodes work by dissipating built-up energy (because of the relay's inability to quickly change electrical current) into the coil's internal resistance. But this doesn't happen in a simple LED circuit!!

What am I missing? This is doing my head-in - need your help!!

Don

Thank you all for your advice - I have gone with couple of resistors and this has sorted the problem

Just make sure you did it safe & so when a resistor is installed it isn't at time what's above.

HEAT MUST GO SOMEPLACE!

Is there a shielded case?


Something like this?