Have a think about it. I have changed my abs unit and the two units in the car and my light is still on. I have cleaned all four sensors but without jacking the car up and running it I can't work out which one is faulty.
So jack the car up...
Or you can use a dvm to measure the voltage from each sensor as it turns.
Measure it at the abs unit connector. Spin each wheel at same pace should give same volts over the 2(?) Wires...