What month/year is your X5? I am not familiar with the diesels, but the the transfer case gear is only seen on later gas models. If you have an earlier one, that may be something that could be eliminated (or move higher on the list).

The wheel speed sensors can be intermittent for a variety of reasons. Heat can open a circuit that is close to total failure, etc.

The codes should be stored until cleared and those can be seen with some software. Of course, it is always better to be able to diagnose it when it is making the actual fault.

Be aware that when those lights are on, the ABS and DSC is disabled. You would have normal braking, but not the computerized functions.

The DSC computer module itself can go bad (an internal connection pops off) - this is what happened to mine - in the US there are a few companies that will recondition it and return it to you. Don't know about where you are. If you get a new one (about US$400) then it needs to be coded to the VIN in the car - something a dealer or well equipment BMW shop can do or someone very good with the eBay software.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles