So the typical reason for intermittent wheel sensor is rust on the sensor ring.
Unfortunately it's quite difficult to deep clean (usually involves removing the CV axle) but I would try this:
Lift both front wheels so you can turn the wheel: remove the sensor and use long cotton swabs with cleaning agent while turning the wheel (it will be hard to turn the rotor solo but you can clamp a breaker bar into two lug bolts to create a crank: put a deep well socket on the breaker bar for a handle)
If you get a fair amount of rust out of the sensor ring it's a good chance that was the problem.
If you don't, sadly the next most likely problem is the abs module itself: the welded wires inside tend to break. When they do they usually still touch some of the time giving intermittent readings. There are services for $150-250 to fix this problem.
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2011 E70 • N55 (me)
2012 E70 • N63 (wife)
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