Most common problem is one of the reluctor rings is cracked, rusted or fallen off!
Google "vauxhall reluctor ring" for more info.
Other things can go wrong (wheel sensors, cables/connectors and ABS pumps can all fail) and a diagnostic computer will tell you where the problem is but have a look yourself first, if a ring is loose or missing it'll be fairly obvious!
The brakes will still work as normal, you just wont have the anti-lockup function.
This is, however, an MOT failure.
If you need diagnostics go to an independent, should be about £30 for a basic code read.
nfh, September 2009
