The ABS light is on. Doesn't go out.

It used to be fine, then one day decided to stay on.

I replaced the front struts shortly before the ABS light problem, though it was all OK after the job, just started a couple of weeks after.

I've checked the wiring/connectors to the wheel sensors and they all seem to be OK, as was the wiring to the ABS unit by the fuse box. I cleaned the exteriors of the wheel sensors (did not remove them) as they were dusty.

I'm guessing a faulty wheel sensor? How can I tell which one it is or if it is something else??

Thanks in advance for any replies/advice/solutions/ideas!!

Brakes haven't been worked on since a fluid change at BMW 10 months ago.