So, I was working on a buddy's car today that had a CEL #41 (primary O2). The problem is that he's already replaced it with a new sensor and the CEL is still there. I did a couple diagnostic checks like resetting the ECU, checking all fuses and we even tried another O2 sensor that I had laying around, but I know is good. It still threw the code. I had him unplug the secondary O2 sensor and it did throw the other code so it was checking the system.

I even rewired the O2 sensor because it was a Bosch replacement with this wacky connector on it. I know the wires are right and it really bothers me that we tried a sensor that we knew was good and it still threw the code.

Any ideas?