So my gsr started throwing a check engine light. I read the code using the paper clip method. It read as a cel code 61 (primary o2 sensor circuit) so I replaced the o2 with a ntk sensor and the light went away. Now 4 days later the codes back. My question is what should my next step be I was going to reset the ecu and check the sensor harness for rips/nicks anything else I should check. The car isn't running poorly infact it seemed to be getting better mpg sense I replaced it but now the codes back. Any ideas what could be the cause?