hi Michael Whitworth
when i tested the ground with a scope it gave a reading of 1v and the O2 sensor wasn't switching i must admit to not checking the rear sensor but having checked the ground all the way back to ecu on all 4 cars that i have dealt with i found the same symptom and the same repair has proved to be ok

could you explain how a ground can be "pulled up"
as surly a ground is a ground and should be less then .2v