Guys,
I had the same issue with my 07 523i LCi earlier!
It was just caused by dirty optical disc which I cleaned it after very expensive lesson learned. ... changed battery, alternator, 2 tie rods complete with ends, powersteering fluid.
Almost gave up until I finally got into the optical disc..
In future, try clean the disc first.
Btw, anyone keen to buy my confirmed in good condition 180amps original bosch alternator, 1.5 yo din100 battery, used tie rod sets?