It is almost definatly one of the wheel bearing assemblies that are shot.
The ABS sensor is built into the bearing assembly. You can test them with an OHM meter to see if you can find a dead one. Otherwise call around. Midas in the US will tell you exactly what is wrong for $50.
The other way around testing is to purchase 2 hub assemblies (1front & 1 rear) dont mount them, just go around the car and test them to see if the light goes out. Take the one back you dont need.
You should be able to buy these at your local parts store for half the price of the dealer.
Midas wanted $600 to fix the problem, the local garage wanted $400, I did it for $200 including the scan cost.