There is a low beam warning under normal circumstances. I'm betting your ALC module (headlight leveling control module under the headlight) failed. Probably due to water or coolant intrusion. The LCM disables the low beam on a headlight where the self leveling is not functional. I just recently dealt with this as well. I made a thread with a workaround, but have not fixed it yet as it requires opening the headlight in my case.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
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