I had to clear that CEL everyday for a couple months before the ECU just gave up. Cant think of a logical explanation, but it just stoped.
If you tie the sensor up somewhere safe (it gets hot, some poeple wrap it in foil) under the car, the ECU may think everything is fine. The front o2 sensor see the typical voltage swings we think of. The rear doesnt see as much amplitude since the CAT affects it in that fashion. When you remove the cat, the front and rear sensor see the same exhaust exhaust, and output the same signal, and the ECU gives the typical "cat system efficiency below threshold, bak 1" CEL. If you take it out of the exhaust, it wont cycle at all, and the ECU usually thinks everything is working fine
