unless you have specialised measuring equipment, checking the signal from the wheel speed sensors is near impossible. You need an oscilloscope to graph the wave patterns. As these are self-powered sensors, the most the average bloke can check for is power and a good earth at the ABS module with a multimeter.
What symptoms apart from the fault light does the car present?
At a longshot it could be a sensor problem, as the system will expect to see a good reading from all wheels when the car moves - (the computer compares each sensor to the other wheels, and when it sees one wheel with no signal it considers this wheel locked by the brakes...the problem is that the brake pedal switch isn't pressed, so it goes into fault mode).
Try checking all 4 wheel speed sensors for correct gap (approx 1 mm) between the tip and the tone wheel that it reads.
Check that all the tone wheels are clean and nothing is blocking the holes (these are magnetic and sometimes dust, metal filings and anything else ferrous will cling to it)
Check all the wiring plugs are tight and each connecting wire isn't damaged or broken where it goes through the strut tower into the body. Sometimes road debris can damage this.
Failing this, you'll need to get your hands on a tech2 or equivalent scan tool and read the live data from the ABS system when the car is rolling to see what's going on.
Don't waste money on guess-repairs. Too many people out there have a second ECU/module/sensor/*insert part* that has nothing wrong with it, but was repleaced through frustration. Unless it's a cheap trial part, sometimes spending a couple of bucks getting the right diagnosis is a good investment.
See how you go and keep me posted
