the abs light comes on to warn the system is faulty. usually a wheel speed sensor or the wires leading to it. disconnect the sensor take a resistance reading from each corner as you turn the wheel you may find one is very different to the other three if it is replace it if not check continuity of the wiring from the sensor to the control unit. the control itself is nearly 100% reliable unless it gets wet. hope this helps
simon smith
November 2009
It could be due to dirt on the reluctor rings (one per wheel) or severed wires going to them. Worth a check!