Originally Posted by fraser9764

If one of the sensors was out of spec the light would stay on from is initial test period when you turn the ignition on. It will be a sensor not picking up properly I'm sure you can measure the ac voltage across the sensor when you spin the wheel. I can't remember of the top of my head what sort of result you should get though.
Do a search for posts containing abs by a bloke called jon@work I'm sure he had posted up some good technical info.