P1275 Cel?

[j.fro]

Since the problem is only on one side of the engine, try putting the left O2 sensors on the right and the right ones on the left. If the code stays on the same side, the problem is not the sensors. If the code moves with the sensors, it's them. Then, if that's the problem, I'd try swapping just the sensors in front of the cats and seeing what happens to the code. If it moves, the problem is the front sensor. If it stays put, it's the rear.