Why is my BMW X5 heads up display not working?

The heads up display in the BMW X5 is known to intermittently fail; if this is Your case (it works sometimes, and not others) -- there is no known diagnosis or fix, other than total replacement. A number of different drivers have reported takeng it to a dealership, who have been unable to replicate or resolve the issue. If, instead, Your HUD never works, there's not much You can do in terms of a fix. Therefore, unfortunately, this will necessitate total replacement. The good news is that while the module can be somewhat expensive (especially on newer model BMW X5s), the process to replace it shouldn't take You too long as it's fairly simple -- maybe a long afternoon or two at worst.