Term, as Slick suggested it might be the alternator. I had similar problems on my n62 one and it was the voltage regulator. I used the cluster to read the voltage though (Test 9 I think) which showed under and over voltage even over 16V. It was throwing all sorts of codes when the voltage reached that level.

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4.8is 2004 imola red
4.8is 2005 Black on Black - DINAN/2 sold
4.4 2004 X5
2003 330xi
2008 328xi - sold
4.4 2000 X5 - sold