Genuine OEM xenon ballast for the D2S bulb. If your bulb is flickering or out it could very well be your ballast. The easiest way to find out if it is either the ballast or bulb is to switch the bulbs from side to side and see if they work. If the bulb turns on it is the ballast, if it doesn't it is the bulb. Replace your broken ballast with this Genuine OEM replacement.