[Mike R]

I guess when one goes, like coil-packs, that's an indication to replace them all.....

However, I do know that from experience they can just randomly "lose" the connection to the speed sensor. I have only had this happen once though and typically it was on my way to the 'ring (and the first time I was taking the CSL), so I was reluctant to run it with out traction control operational for my first outing there in a new to me car.

I was really lucky (like Craig) that there was a guy there from Scotland with his own E46 M3 who was a whiz with INPA and had his lap-top with him. He plugged it in and immediately diagnosed that it was one of the wheel-speed sensors, where the DME had somehow become confused and decided it didn't want to communicate with one of them. He reassigned it and it's never been a problem since (and that was 8 years ago)....

Total cost - I had to give him a passenger lap .