Overview Some vehicle manufacturers, such as BMW and Audi, use alternating current on new vehicles to extend the lifetime of halogen bulbs. This is also often the case on DRLs, to achieve a lower brightness level during the day. Specifically, this is called Pulse Width Modulation. HID conversion kits require continuous current to operate correctly. If HIDs are installed onto a DRL circuit, the lights will flicker very quickly when the vehicle is turned on. If you have a relay, it will buzz loudly. The solution for this is the Warning Canceller Module. The HID Warning Canceller Module is also known as an HID Error Message Canceller, HID Decoder, HID Anti Flicker Capacitor, or Canbus Killer, because it will also eliminate "bulb out" or "bulb failure" warnings in most Mercedes, BMW, Audi, VW, and other cars when HIDs are installed.