I had an idea. My wife has a chevy also with no engine ight warning. I found the fuse for its o2 sensor and performed the same two checks as i did in my car. Her fuse was good ,naturally, but the fuse site registered .01 v, not the 12 v i expected.
So for wharever reason, voltage is not present at the fuse. Maybe the fuse is on the neutral leg, and voltage goes directly from battery to sensor??