Another possibility, although rare, would be that the sensor itself is not grounded. It may be possible that if you used some type of thread sealer the path to ground has been blocked. Either do a voltage drop test with multi meter or run ground wire from battery negative to sensor body. This just needs to be a temporary rig to test this possibility. Another thought; defective new part. If the ground checks out ok, see what the parts store will do for you.
