Is the 02 sensor connected? You might check the plug and wiring. I have never seen even a bad sensor that would not give a reading. My only other thought is, replace it with a known good sensor and see. Or you might have to get a wiring diagram and do a pin out check of the wiring from the ecm to the sensor. I would do the wiring check 1st. If a scanner is not reading a sensor, probably a wiring or ecm problem. Hopefully this guides you in the right direction.