The white smoke is perhaps indicative that you got a dose of water with your diesel fill up... You could try extract some of the diesel and put in in a clear bottle, if there is water it should be visible, either seperated out or milky appearance. Happened to me a few years ago and I had to have the tank drained and the system flushed with diesel injector cleaner, but after that it was fine.

The level sensors can sometimes get stuck and it's worth having a look under the rear to see if it's moving freely. You have to jack the rear up or do some serious grovelling to see it but it is possible, maybe need to take the wheel off...

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X5 2006 3.0d M57N
GA6HP26Z Tranny
180,000km