Anyone with Vagcom can code them for you
Des basically for the fault system to work the central electric module sends a pulse to all parts of the car when it gets a reply it says the system is fine, Xenons cannot work on a pulsed system which is why you see the xenons flicker if not coded in...once coded the central electrics will send a constant power supply to the xenon ballast(power pack) and that fires the ignitors. Hope that throws some light on it pardon the punDarren