I Had the same problem, and it required replacing the HID control unit ( the special ballast dedicated to the HID).

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Current:
2008 BMW X5 3.0 Space Grey/ Tan
2009 Audi A4 2.0T Ibis White/Black
2017 Porsche Macan Black/ Garnet Red

Past:
2013 Mercedes C300 Palladium Silver/ Black-- sold & missed
2011 Buick Regal-- sold
2006 Jeep Liberty Limited White/ Grey -- RIP
2004 Jeep Liberty Limited Blue/ White-- RIP