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My understanding is that the light will come on if the sensor circuit is open (sensors removed) or if one is shorted to ground.

I replaced my pads last May and reused the old sensors. Two weeks later I was at the track and the brake light came on. I inspected all the pads and fluids and everything checked out A-ok but a failed master cylinder might be hard to spot. I didn't want a braking issue at 120+ so I ended my day early. When I got home I pulled the sensors out and found one had gotten really hot and was grounding out. Maybe I didn't have it inserted into the pad properly. I insulated all 4 sensors with some heat shrink tubing and zip tied them back per others instructions and the light is gone. I re-inspect my pads and sensors every time a wheel is off and all is well so far.

I hope this helps.