what are the symptoms of a dodgy abs sensor?

would it stop me bleeding the caliper?

i changed the front discs and pads on my rs2000 and bled one side but the other wouldn't bleed for some reason but after a few goes it did let a little bit go but not much, not really enuff to ensure no air.....

anyways wen i brake, the same caliper is sticking on and i can feel wat must be the abs pump going.

if it is the sensor wat is the best method of cleaning them in case thats wat it is?